DURABILITY BY DESIGN - A GUIDE FOR RESIDENTIAL BUILDERS AND DESIGNERS

by HUD USER

U.S. Department of Housing and Urban Development
Office of Policy Development and Research
DURABILITY
BY DESIGN
BY DESIGN
A Guide for Residential Builders and Designers

PATH (Partnership for Advancing Technology in Housing) is a new private/public effort to develop, demonstrate, and
gain widespread market acceptance for the ìNext Generationî of American housing. Through the use of new or
innovative technologies, the goal of PATH is to improve the quality, durability, environmental efficiency, and affordability of
tomorrowís homes.
PATH is managed and supported by the U.S. Department of Housing and Urban Development (HUD). In addition, all
federal agencies that engage in housing research and technology development are PATH Partners, including the
Departments of Energy, Commerce, and Agriculture, as well as the Environmental Protection Agency (EPA) and the
Federal Emergency Management Agency (FEMA). State and local governments and other participants from the public
sector are also partners in PATH. Product manufacturers, home builders, insurance companies, and lenders represent
private industry in the PATH Partnership.
To learn more about PATH, please contact
451 7
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Street, SW
Washington, DC 20410
202-708-4277 (phone)
202-708-5873 (fax)
e-mail: pathnet@pathnet.org
website: www.pathnet.org
Visit PD&Rís website
www.huduser.org
to find this report and others sponsored by

HUDís Office of Policy Development and Research (PD&R).

Other services of HUD USER, PD&Rís Research Information Service, include listservs; special interest, bimonthly

publications (best practices, significant studies from other sources); access to public use databases, and a hotline

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May 2002

Durability by Design

A Guide for Residential Builders and Designers
Prepared for
U.S. Department of Housing and Urban Development

Washington, DC

Contract No. C-OPC-21289 (T-002)
by
NAHB Research Center, Inc.

Upper Marlboro, MD

May 2002

ACKNOWLEDGMENTS

This guide was written by the NAHB Research Center, Inc. with support from the U.S. Department of
Housing and Urban Development. The NAHB Research Center had generous contributions from many
groups and individuals who have helped to develop the practices and methods that make houses stand the
test of time. The primary author of this guide at the NAHB Research Center was Jay Crandell, P.E..
Contributing authors and reviewers include Michael Grothe, James Lyons, and Jeanne Leggett Sikora.
Illustrations and figures were drawn by Elliott Azzam.
NOTICE
The work that provided the basis for this publication was supported by funding under a grant with the
U.S. Department of Housing and Urban Development. The substance and findings of the work are dedicated
to the public. The authors are solely responsible for the accuracy of the statements and interpretations
contained in this publication. Such interpretations do not necessarily reflect the views of the Government.
While the information in this document is believed to be accurate, neither the authors, nor reviewers, nor
the U.S. Department of Housing and Urban Development, nor the NAHB Research Center, Inc., nor any of
their employees or representatives makes any warranty, guarantee, or representation, expressed or implied,
with respect to the accuracy, effectiveness, or usefulness of any information, method, or material in this
document, nor assumes any liability for the use of any information, methods, or materials disclosed herein,
or for damages arising from such use.
ABOUT THE NAHB RESEARCH CENTER
The NAHB Research Center, Inc. is a not-for-profit subsidiary of the National Association of Home
Builders (NAHB). NAHB has over 203,000 members, including 60,000 builders who build more than 80
percent of new American homes. The Research Center conducts research, analysis, and demonstration
programs in all areas relating to home building and carries out extensive programs of information dissemina
tion and interchange among members of the industry and between the industry and the public.
I

FOREWORD

Few people intentionally consider durability when designing a home, but rather rely on experience and
market acceptance to make design decisions. This approach to design works best in a stable housing
market where architectural preferences and material choices do not change or change very slowly. The
housing market, however, tends to be dynamic rather than stable and new materials and preferences
influence the market continuously, sometimes in dramatic ways. This dynamic condition also places a
responsibility on designers and builders to properly apply their experiences, which are often based on older
construction methods and materials, to new materials and design conditions. As a result, it is important to
understand why certain practices have been effective (or ineffective) in the past so that they can be properly
interpreted and considered in the design and construction of modern homes.
This manual titled Durability by Design: A Guide for Residential Builders and Designers is intended to
raise the awareness and understanding of building durability as a design consideration in housing. The
Guide covers basic concepts of durability and presents recommended practices ó including numerous
construction details and design data ó for matters such as moisture management, ultraviolet (UV)
protection, insects, decay, corrosion, and natural hazards. Some attention is also given to matters that
may be considered serviceability issues related to normal wear-and-tear, aesthetics, or functions not
immediately associated with durability.
The contents of this Guide will help to preserve and promote ìtried-and-trueî practices and concepts
related to housing durability, and present them in a manner that can be used to cost-effectively design the
durable homes of the future.
Lawrence L. Thompson
General Deputy Assistant Secretary for
Policy Development and Research
II

III

Table of Contents

ACKNOWLEDGMENTS -------------------------------------------------------------------------------------------------------------------------------------------I
FOREWORD ------------------------------------------------------------------------------------------------------------------------------------------------------- I I
CHAPTER 1 - INTRODUCTION -------------------------------------------------------------------------------------------------------------------------------- 1
1.1 General ------------------------------------------------------------------------------------------------------------------------------------- 1

1.2 Durability Requires Commitment -------------------------------------------------------------------------------------------------- 2

1.3 Overview ----------------------------------------------------------------------------------------------------------------------------------- 2

CHAPTER 2 - CONCEPTS OF DURABILITY --------------------------------------------------------------------------------------------------------------- 3
2.1 General ------------------------------------------------------------------------------------------------------------------------------------- 3

2.2 What is Durability? -------------------------------------------------------------------------------------------------------------------- 3

2.3 Building Codes and Durability ----------------------------------------------------------------------------------------------------- 5

2.4 Factors Influencing Durability ----------------------------------------------------------------------------------------------------- 5

2.5 Common Durability Issues ---------------------------------------------------------------------------------------------------------- 8

CHAPTER 3 - GROUND AND SURFACE WATER ------------------------------------------------------------------------------------------------------ 11
3.1 General ----------------------------------------------------------------------------------------------------------------------------------- 11

3.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 11

CHAPTER 4 - RAIN AND WATER VAPOR ---------------------------------------------------------------------------------------------------------------- 15
4.1 General ----------------------------------------------------------------------------------------------------------------------------------- 15

4.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 15

CHAPTER 5 - SUNLIGHT ------------------------------------------------------------------------------------------------------------------------------------- 39
5.1 General ----------------------------------------------------------------------------------------------------------------------------------- 39

5.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 40

CHAPTER 6 - INSECTS ---------------------------------------------------------------------------------------------------------------------------------------- 45
6.1 General ----------------------------------------------------------------------------------------------------------------------------------- 45

6.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 45

CHAPTER 7 - PROTECTION AGAINST DECAY AND CORROSION ------------------------------------------------------------------------------- 51
7.1 General ----------------------------------------------------------------------------------------------------------------------------------- 51

7.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 51

CHAPTER 8 - NATURAL HAZARDS ------------------------------------------------------------------------------------------------------------------------ 59
8.1 General ----------------------------------------------------------------------------------------------------------------------------------- 59

8.2 Recommended Practices ----------------------------------------------------------------------------------------------------------- 60

CHAPTER 9 - MISCELLANEOUS --------------------------------------------------------------------------------------------------------------------------- 63
9.1 General ----------------------------------------------------------------------------------------------------------------------------------- 63

9.2 Plumbing -------------------------------------------------------------------------------------------------------------------------------- 65

9.3 HVAC -------------------------------------------------------------------------------------------------------------------------------------- 65

9.4 Exterior Finishes ---------------------------------------------------------------------------------------------------------------------- 66

BIBLIOGRAPHY ------------------------------------------------------------------------------------------------------------------------------------------------- 69
GLOSSARY ------------------------------------------------------------------------------------------------------------------------------------------------------- 72
APPENDIX A - DURABILITY CHECKLISTS ------------------------------------------------------------------------------------------------------------- 73
APPENDIX B - ESTIMATED LIFE-EXPECTANCY OF BUILDING MATERIALS AND PRODUCTS ---------------------------------------- 74
IV

List of Tables

2.1 ñ Top Five Homeowner Warranty Claims ------------------------------------------------------------------------ 9

2.2 ñ Major Expenditures for Repairs, Maintenance,

and Replacements to Owner Occupied Homes (1998) ---------------------------------------------------- 9

4.1 ñ Recommended Minimum Roof Overhang Widths for One- and

Two-Story Wood Frame Buildings ----------------------------------------------------------------------------- 17

4.2 ñ Roof Pitch Factors --------------------------------------------------------------------------------------------------- 19

4.3 ñ Gutter Capacity (roof area served in square feet)

Based on 1 in/hr Rainfall Intensity ----------------------------------------------------------------------------- 19

4.4 ñ Recommended Drainage Plane Characteristics

for Exterior Walls in Various Climate Conditions --------------------------------------------------------- 22

4.5 ñ Drainage Plane and Vapor Retarder Material Properties ---------------------------------------------- 23

4.6 ñ Recommended Vapor Retarder Characteristics for Building Exteriors

or Interiors in Various Climate Conditions ------------------------------------------------------------------ 24

4.7 ñ Roof and Crawl Space Ventilation Recommendations ------------------------------------------------- 36

4.8 ñ Caulk Characteristics and Application Recommendations -------------------------------------------- 37

5.1 ñ Solar Angle Factors ------------------------------------------------------------------------------------------------ 40

7.1 ñ Recommended Finishes for Exterior Wood ---------------------------------------------------------------- 54

7.2 ñ Recommended Preservative Retention Levels for CCA-Treated Lumber ------------------------- 55

7.3 ñ No-Rust Service Life of Nails Exposed to Normal Outdoor Environment ------------------------- 56

8.1 ñ Hurricane Damage Statistics (single-family homes) ----------------------------------------------------- 59

8.2 ñ Northridge Earthquake Damage Statistics (percent of single-family homes) -------------------- 60

V

List of Figures

2.1 ñ The House and the ìDuralogic Cycleî ------------------------------------------------------------------------- 7

2.2 ñ Loss of Function vs. Time for Three Hypothetical Materials

or Products of Different Quality Levels (poor, acceptable, and best) -------------------------------- 8

3.1 ñ Bore Hole Used for Preliminary Site Investigation ------------------------------------------------------- 12

3.2 ñ Site Grading and Surface Drainage--------------------------------------------------------------------------- 13

3.3 ñ Basement Construction and Optional Enhancements for Wet Site Conditions ----------------- 13

3.4 ñ Typical Frost-Protected Shallow Foundation with Perimeter Drain -------------------------------- 14

4.1 ñ Frequency of Moisture Problems in Walls of Selected Buildings in a Moist, Cool Climate 16

4.2 ñ Roof Overhangs ------------------------------------------------------------------------------------------------------ 17

4.3 ñ Climate Index Map Based on Wood Decay Potential --------------------------------------------------- 17

4.4 ñ Roof Gutters and Discharge Methods ------------------------------------------------------------------------- 18

4.5 ñ Rainfall Intensity Map of the United States ----------------------------------------------------------------- 19

4.6 ñ Weather Barrier Construction ----------------------------------------------------------------------------------- 21

4.7 ñ Heating Degree Day (HDD) Map of the United States (65
o
F basis) ----------------------------------- 25

4.8a,b ñ Basic Roof Flashing Illustrations -----------------------------------------------------------------------27, 28

4.9 ñ Eave Flashing for Preventing Ice Dams ---------------------------------------------------------------------- 28

4.10 ñ Window Flashing Illustration ---------------------------------------------------------------------------------- 29

4.11 ñ Window Sill and Jamb Flashing Detail --------------------------------------------------------------------- 30

4.12 ñ Window Flashing for Severe Weather ---------------------------------------------------------------------- 31

4.13 ñ Door and Head Trim Flashing Detail ------------------------------------------------------------------------ 31

4.14 ñ Deck Ledger Flashing Detail ----------------------------------------------------------------------------------- 32

4.15 ñ Typical Brick Veneer Flashing Details ---------------------------------------------------------------------- 33

4.16 ñ Brick Veneer Flashing at Roof Intersections -------------------------------------------------------------- 34

5.1 ñ Solar Radiation Map of the United States ------------------------------------------------------------------- 39

5.2 ñ Effect of Building Latitude on Effectiveness of Overhangs -------------------------------------------- 40

5.3 ñ Effect of Surface Coloration on Solar Heat Gain --------------------------------------------------------- 41

VI

5.4 ñ Illustration of Solarscaping -------------------------------------------------------------------------------------- 42

6.1 ñ Termite Probability (Hazard) Map ------------------------------------------------------------------------------ 46

6.2 ñ Extent of Recorded Termite Damage ------------------------------------------------------------------------- 46

6.3 ñ Use of Termite Shields --------------------------------------------------------------------------------------------- 49

6.4 ñ Use of Concrete as a Termite Barrier ------------------------------------------------------------------------- 50

7.1 ñ Details to Separate Wood from Ground Moisture -------------------------------------------------------- 52

VII

CHAPTER 1
Introduction

1.1 General
Of all the issues that must be considered when
building a home, durability has perhaps the broadest
impact on long-term performance, the most complex
set of physical interactions, and the largest potential
economic consequence. Fortunately, many of the
best practices intended to improve durability require
little more than good judgment and a basic knowledge
of the factors that affect building durability.
A fundamental element of this discussion is the
very meaning of durability. For this guide, durability
may be defined as the ability of a material, product, or
building to maintain its intended function for its
intended life-expectancy with intended levels of
maintenance in intended conditions of use.
1
Obvi
ously this definition may take on different meanings
for different groups (e.g., builders, homeowners,
manufacturers), implying that communication and
education are key aspects that affect durability.
Addressing durability is not a pursuit of extremes,
but rather a pursuit of cost-effectiveness in terms of
initial and long-term (i.e., maintenance, replacement)
costs. Trying to make a home too durable can add so
much to the cost of a new home that it may deny
access to the basic need of decent shelter in the
present time. Erring in the other direction can result
in an equally disastrous future in terms of homeowner
complaints, unsafe or unhealthy living conditions, and
excessive maintenance and repair costs.
The above comparison assumes that there is a
direct trade-off between durability and affordability of
homes. While the saying, ìyou get what you pay forî,
is generally true, there are many design and construc
tion practices that have minimal construction cost
impacts, and significant durability benefits. The
benefits may be measured in terms of maintenance,
repair, general function of the home and its compo
nent parts over time, enhanced business reputation,
and customer satisfaction. Moreover, many such
practices are well-known and need not be re-invented,
but only communicated to the builder, designer, and
consumer.
1
For a standardized definition of durability, refer to ASTM E632-82 (1996) Standard Practice
for Developing Accelerated Tests to Aid Prediction of the Service Life of Building
Components and Materials, American Society of Testing and Materials, West
Conshohocken, PA (www.astm.org)
Introduction
This guide strives to reinforce ìtried and trueî
practices that add to the durability of homes, shed
some light on areas of confusion, and identify
important trade-offs between cost and durability that
should be carefully considered by the designer,
builder, and homeowner. The guide focuses on
practical solutions in key areas that are known to
create significant and reoccurring durability problems.
The guide also identifies timeless design concepts
and principles that, once understood, can be applied
to a variety of conditions and applications in modern
housing design, construction, and maintenance.
Finally, an attempt is made to draw attention to
innovative materials and techniques that hold promise
for improved durability in houses of the future.
WHY IS DURABILITY IMPORTANT?
ƒAvoidance of short-term durability or
performance problems (i.e.,
callbacks) is important to the
builderís and designerís reputation
and business profitability.
ƒThe long-term condition of a home is
important to retaining its investment
value as well as its continued function
as a safe, healthy, and aesthetic living
environment.
ƒPoor durability adds to the operating
and maintenance cost of home

ownership.

ƒFailure to meet reasonable
expectations for durability increases
liability exposure.
ƒPeople donít like maintenance (i.e.,
high durability and low maintenance
are important sales and purchasing
factors).
ƒNew products designed without
adequately considering durability can
prematurely fail, leading to both
customer dissatisfaction and
manufacturer losses.
1

Chapter 1
DURABILITY CHECKLISTS
To assist in using this guide and in
applying selected recommended
practices, a durability checklist is
provided in Appendix A. It lists
various actions or considerations that
should occur during the course of
designing and constructing a house.
Also included are action items
appropriate for homeowners. Feel free
to use and modify the checklist to suit
your needs and level of interest.
1.2 Durability Requires
Commitment
Building and designing a durable home does not
require a building scientist or durability specialist, but
it does require commitment. Achieving durable
construction not only includes the basicsómaterial
selection, verification of manufacturer warranties, and
passing minimum code-required inspectionsóbut it
also involves a reasonable consideration of key details
in the production of a home and understanding of the
interactions between different materials and trades.
Furthermore, durability also requires the appropriate
use and installation of specified materials and, equally
important, the functional integration of various
materials and products such that the house performs
as intended. In tandem, durability design criteria
should incorporate concepts such as ease-of-repair or
replacement where appropriate.
Building a durable home is relatively simple if the
right information and guidance is available. In fact,
including durability as a design criterion (though often
subjective in nature) can add marketable features to
homes at very little additional cost or design effort.
Some features may already be incorporated into
existing designs while others can be added through a
simple modification of plans and specifications.
Admittedly, although some aspects of designing
for durability are rather straight forwardó such as the
building code requirement of keeping untreated wood
from contacting the groundó other tasks may involve
somewhat greater effort. Achieving cost-effective and
durable construction requires a reasonable commit
ment in the planning, design, and construction of
houses.
1.3 Overview

This guide is arranged in the most practical and
user-friendly way possible. However, there are
many interrelated topics, which make any arrange
ment of information on durability somewhat
challenging. To the degree possible, redundancy in
content is minimized and interrelated topics or
discussions are appropriately cross-referenced so
that the reader can seek the depth of information
needed with relative ease. A glossary is provided at
the end of this guide to aid in the proper under
standing of this writing.
The chapters of this guide are organized mainly
by the factors that affect durability, i.e., ground and
surface water, rain and water vapor, sunlight, etc.
Within each chapter, the first section is always
directed toward a general understanding of the
concepts and issues related to the specific topic(s)
of the section. An effort has been made to include
geographically-based data and other technical
information that allows the reader to quickly
determine the relevance of a particular durability
issue to local conditions or requirements.
Chapter 2 introduces the topic of durability and
presents some important over-arching concepts and
issues that create a foundation of understanding
upon which the remainder of the guide builds.
Chapter 3 addresses concerns related to ground
and surface water, primarily affecting site and
foundation design. Chapter 4 addresses rain and
water vapor and their effect on the above-ground
structure. Combined, Chapters 3 and 4 cover some
of the most prevalent housing durability issues
related to wateróthe most formidable durability
factor known to man. Chapter 5 deals with sunlight
and methods to mitigate the effects of ultraviolet
(UV) radiation on building materials. In Chapter 6,
methods to prevent insect infestation and damage
are presented. Chapter 7 addresses the issue of
wood decay and corrosion of metal fasteners, both
associated with the effects of moisture. Practices to
improve the durability of homes that are subject to
natural hazards, such as hurricanes and earth
quakes, are presented in Chapter 8. Finally,
Chapter 9 covers several miscellaneous and
ìserviceabilityî issues related to durability, including
items such as wear-and-tear, nuisances, plumbing/
mechanical/electrical systems, and exterior
appurtenances.
2

CHAPTER 2
Concepts of
Durability
2.1 General
In this chapter, some fundamental concepts of
durability related to the design of residential buildings
are addressed. This background information is
intended to establish a baseline of understanding and
to introduce concepts and information important to
developing a balanced perspective regarding durability.
Before discussing the concept of durability, some
discussion on unrealistic notions surrounding the
topic of durability is in order. Despite the best efforts
of the most knowledgeable and capable people,
unforeseen problems will continue to occur in homes
(e.g., premature failures of building products,
components, and systems). This undesirable
outcome is often a consequence of taking calculated
risks in moving toward more resource efficient,
affordable, functional, and appealing homes. Further, it
is impractical to think that the durability of all building
components and systems can be exactly designed
and crafted such that they all last just as long as
intended. (This point is a matter of poetic parody, see
inset of ìThe Wonderful One-Hoss Shayî by Oliver
Wendell Holmes on the following page). In fact, the
service life of building materials and products varies
substantially (see Appendix B ñ Estimated Life-
Expectancy of Building Materials and Products).
Thus, it can be expected that some components of a
home will require some vigilant attention along the
way (i.e., maintenance, repair, and eventual replace
ment of ìworn-outî components).
Note that many changes have occurred in home
building over the past several decades that will likely
affect the durability of houses in the short and long
termñsome good and some bad. Examples of
material changes include the increased use of
engineered wood products, adhesives, and plastics,
among many others. At the same time, housing
designs have tended to grow in complexity and size,
thereby increasing exposure to the elements and
vulnerability. Also, newer materials and technologies
have changed both the susceptibility and exposures
of building materials in modern homes. New homes
are also increasingly complex to operate and
Concepts of Durability
maintain. In short, there are more durability issues to
deal with and more material choices than ever before.
2.2 What is Durability?
Durability is the ability of a material, product, or
building to maintain its intended function for its
intended life-expectancy with intended levels of
maintenance in intended conditions of use. However,
we all know that the road to success is not just paved
with good intentions. Ultimately, what is built must
work as expected, or as nearly so as practicable.
What is a reasonable expectation or goal for
durability? It depends.
It depends on how much it costs. It depends on
the expectations of the end user and the long term
investment value of the product. It depends on the
local climate. It also depends on expected norms
when the end user is not intimately involved with or
knowledgeable of various design decisions and their
implications. It also depends, of course, on the
material itself.
For example, a house is expected (at least in
theory) to last for 75 years or more with normal
maintenance and replacement of various components
(see Appendix B ñ Estimated Life-Expectancy of
Building Materials and Products). But then again,
what one person considers normal maintenance may
be perceived differently by another. Durability is,
therefore, an exercise in the management of expecta
tions as well as an application of technology. For this
reason, some builders and designers make significant
efforts to inform their clients and trade contractors
about reasonable expectations for the durability,
performance, maintenance, and operation of a home.
Some references to help in this matter include:
ƒ Caring For Your Home: A Guide to Maintaining
Your Investment (NAHB/Home Builder Press,
1998);
3

Chapter 2
THE DEACON’S MASTERPIECE: OR THE WONDERFUL “ONE-HOSS SHAY”
Oliver Wendell Holmes
Have you heard of the wonderful one-hoss shay,
That was built in such a logical way
It ran a hundred years to a day,
And then, of a sudden, itñah, but stay,
Iíll tell you what happened without delay,
Scaring the parson into fits,
Frightening people out of their wits,ñ
Have you ever heard of that, I say?
Seventeen hundred and fifty-five.
Georgius Secundus was then alive,ñ
Snuffy old drone from the German hive.
That was the year when Lisbon-town
Saw the earth open and gulp her down,
And Bradockís army was done so brown,
Left without a scalp to its crown.
It was on the terrible Earthquake-day

That the Deacon finished the one-hoss shay.

Now in building of chaises, I tell you what,

There is always somewhere a weakest spot, ñ

In hub, tire, felloe, in spring or thill.

In panel, or crossbar, or floor, or sill,

In screw, bolt, thoroughbrace, ñlurking, still,

Find it somewhere you must and will, ñ

Above or below, or within or without, ñ

And thatís the reason, beyond a doubt,

A chaise breaks down, but doesnít wear out.

But the Deacon swore (as Deacons do,

With an ìI dew vum,î or an ìI tell yeouî)

He would build one shay to beat the taown

ëNí the keounty ëní all the kentry raouní;

It should be so built that it couldnít break daown.

ñîfur,î said the Deacon, ìëtís mighty plain

Thut the weakesí place musí staní the strain;

ëní the way tí fix it, uz I maintain, is only jest

Tí make that place uz strong uz the rest.î

So the Deacon inquired of the village folk

Where he could find the strongest oak,

That couldnít be split nor bent nor broke, ñ

That was for spokes and floor and sills;

He sent for lancewood to make the thills;

The crossbars were ash, from the straightest trees,

The panels of white-wood, that cuts like cheese,

But lasts like iron for things like these;

The hubs of logs from the ìSettlerís ellum,î ñ

Last of its timber, ñthey couldnít sell ëem,

Never an axe had seen their chips,

And the wedges flew from between their lips,

Their blunt ends frizzled like celery-tips;

Step and prop-iron, bolt and screw,

Spring, tire, axle, and linchpin too,

Steel of the finest, bright and blue;

Thoroughbrace, bison-skin, thick and wide;

Boot, top, dasher, from tough old hide

Found in the pit when the tanner died.

That was the way he ìput her through.î ñ

ìThere!î said the Deacon, ìnaow sheíll dew.î

Do! I tell you, I rather guess

She was a wonder, and nothing less!

Colts grew horses, beards turned gray,

Deacon and deaconess dropped away,

Children and grandchildrenñwhere were they?

But there stood the stout old one-hoss shay

As fresh as on Lisbon-earthquake-day!

EIGHTEEN HUNDRED; ñit came and found

The Deaconís masterpiece strong and sound.

Eighteen hundred increased by ten; ñ

ìHahnsum kerridgeî they called it then.

Eighteen hundred and twenty came; ñ

running as usual; much the same.

Thirty and forty at last arrive,

And then came fifty, and FIFTY-FIVE.

Little of all we value here

Wakes on the morn of its hundredth year

Without both feeling and looking queer.

In fact, thereís nothing that keeps its youth,

So far as I know, but a tree and truth.

(This is a moral that runs at large;

Take it. ñYouíre welcome. ñNo extra charge.)

FIRST OF NOVEMBER, ñthe Earthquake-day. ñ

There are traces of age in the one-hoss shay,

A general flavor of mild decay,

But nothing local, as one may say.

There couldnít beñfor the Deaconís art

Had made it so like in ever part

That there wasnít a chance for one to start.

For the wheels were just as strong as the thills,

And the floor was just as strong as the sills,

And the panels just as strong as the floor,

And the whippletree neither less nor more,

And the back-crossbar as strong as the fore,

And spring and axle and hub encore.

And yet, as a whole, it is past a doubt

In another hour it will be worn out!

First of November, fifty-five!

This morning the parson takes a drive.

Now, small boys, get out of the way!

Here come the wonderful one-hoss shay,

Drawn by a rat-tailed, ewe-necked bay.

ìHuddup!î said the parson.ñOff went they.

The parson was working his Sundayís text, ñ

Had got to fifthly, and stopped perplexed

At what theñMosesñwas coming next.

All at once the horse stood still,

Close by the meetíní-house on the hill.

First a shiver, and then a thrill,

Then something decidedly like a spill, ñ

And the parson was sitting upon a rock,

At half-past nine by the meetíní-house clockñ

Just the hour of the Earthquake shock!

What do you think the parson found,

When he got up and stared around?

The poor old chaise in a heap or mound,

As if it had been to the mill and ground.

You see, of course, if youíre not a dunce,

How it went to pieces all at once, ñ

All at once, and nothing first, ñ

Just as bubbles do when they burst.

End of the wonderful one-hoss shay,

Logic is logic. Thatís all I say.

4

ƒ Your New Home and How to Take Care of It
(NAHB/Home Builder Press, 2001); and
ƒ A Builderís Guide to Marketable, Affordable,
Durable, Entry-Level Homes to Last (HUD,
1999).
2.3 Building Codes and
Durability
Numerous requirements found in building codes
imply a minimum level of durability performance or
expectation. Building codes specify the minimum
type and nature of various materials, including
certain installation requirements that may vary
according to local or regional climatic, geologic, or
biologic conditions.
Despite the extensive framework of require
ments found in building codes, there are still gaps
in the details or in the reliability of the information
for any specific application or local condition. In
some instances, the requirements are clear, e.g., ìa
metal connector with minimum G60 galvanic
coating shall be usedî and in other cases the
guidance is quite vague, e.g., ìuse corrosion
resistant fasteners.î Likewise, standardized
durability tests for materials are rarely calibrated to
performance in actual conditions of use.
Further, building codes and standards are often
driven by various opinions and data or experiences
expressed in the code development process.
Sometimes the evidence is contradictory or
incomplete. Nonetheless, it is legally required that a
builder and designer adhere to code prescribed
requirements related to durability and, when
deemed appropriate, seek approval of alternate
means and methods of design or construction that
are at least equivalent to that required or implied by
the locally approved building code.
The major U.S. model building codes currently
available are listed in the sidebar to the right.
However, the reader should be informed that earlier
versions may be in use locally since these codes
do not become law until they are legislatively
adopted at the local level. In addition, these national
model codes are often amended to address local
issues and concerns.
Concepts of Durability
2.4 Factors Influencing
Durability
The manner in which materials and buildings
degrade over time depends on their physical make
up, how they were installed, and the environmental
conditions to which they are subjected. It is for this
reason that environmental conditions, such as
humidity and temperature, are carefully controlled in
museums to mitigate the process of degradation.
Even then, artifacts still require periodic care and
maintenance.
Houses, depending on where they are located
with respect to geology and climate, are more or
less subjected to various types of durability
ìfactors.î Each of the ìfactorsî listed below, which
can be managed but not externally controlled, is
addressed in this guide:
ƒ Moisture
ƒ Sunlight (UV radiation)
ƒ Temperature
ƒ Chemicals
ƒ Insects
ƒ Fungi
ƒ Natural Hazards
ƒ Wear and Tear
In essence, a house is part of an environmental
cycle as depicted in Figure 2.1 and is subject to the
same powerful forces of nature that create and then
erode mountains, cause organic matter to decom
pose, and change the face of the earth.
MODEL U.S. BUILDING CODES
ƒOne- and Two-Family Dwelling Code
(OTFDC), Council of American
Building Officials (CABO), Falls
Church, VA, 1995.
ƒInternational Residential Code (IRC),
International Code Council, Inc.,

Falls Church, VA, 2000.

ƒInternational Building Code (IBC),
International Code Council, Inc.,

Falls Church, VA, 2000.

ƒUniform Building Code (UBC),
International Conference of Building
Officials (ICBO), Whittier, CA,

1997.

ƒStandard Building Code (SBC),
Southern Building Code Conference
International (SBCCI), Birmingham,
AL, 1999.
ƒNational Building Code (NBC),
Building Officials and Code
Administrators International, Inc.,
Country Club Hills, IL, 1999.
5

Chapter 2
Over the course of time, the greatest concerns
(and impacts) regarding durability are those pro
cesses that occur constantly over the life of a home.
Most notable of these factors is moisture. Moisture
comes in many forms (i.e., rain, snow, ice, vapor) and
is linked to other durability factors. For instance,
moisture must be present in sufficient quantity to
promote corrosion (e.g., chemical degradation), insect
habitation (e.g., subterranean termites), and rot (e.g.,
wood decomposition). By controlling exposure to
moisture, many other durability problems are also
solved. Other problems, such as mold and indoor air
quality, are also related to moisture. It is for this
reason that there is a major emphasis on moisture in
this guide. In fact, the effects of moisture on building
durability have been associated with enormous
economic impact in the United States for wood
construction alone.
The UV radiation from sunlight also has a
tremendous impact on the exterior finishes of homes.
For example, sunlight causes coatings to chalk-up or
fade in color, plastics to degrade, wood to weather,
and asphalt roof shingles to become brittle. Sunlight
can also fade carpets, drapes, and furnishings inside
homes. In relation to moisture, sunlight can heat
surfaces and drive moisture into or out of materials
and buildings; intermittent sunlight can also cause
temperature cycling.
Temperature causes materials to expand and
contract. Temperature cycling, particularly in the
presence of water, can cause some materials to
weaken or fatigue. Thermal expansion and contraction
can also cause materials to buckle and warp and,
therefore, become less effective in their intended
function (e.g., buckling of improperly installed siding
which may allow increased rain water penetration).
When temperature cycles above and below the
freezing temperature of water, even more damaging
effects can occur to materials with high moisture
content.
Chemical reactions, most often occurring in the
presence of water, are responsible for a variety of
durability problems and can dramatically accelerate
otherwise normal rates of degradation. For example, a
galvanic reaction between dissimilar metals can
cause one metal to degrade relatively rapidly. This
effect is evidenced by more rapid corrosion of
galvanized fasteners in preservative-treated wood (i.e.,
chromated copper arsenate or CCA) relative to
untreated wood. Another example is the pitting of
copper piping due to the presence of certain salts and
minerals in water or soil.
Certain insects are particularly fond of wood and,
in fact, depend on wood for food. In the presence of
wood-consuming insects such as termites and
carpenter ants, an unprotected wood-frame home is
nothing more than a free food source.
Natural hazards form a special class of durability
concerns that are generally associated with localized
climatic or geologic conditions. These conditions are
generally considered from a life-safety perspective,
but they are considered here in the broader sense of
durability. For example, a life-safety provision in a
building code may require that an extreme wind or
earthquake event be considered in the structural
design of a home. However, durability impacts may be
realized in even moderate or mild natural events. Even
a mild hurricane can cause significant water penetra
tion and salt deposition resulting in immediate (e.g.,
flooding) and long-term (corrosion, mold growth)
damage. Natural hazards that affect durability include
hurricanes, earthquakes, floods, wildfires, hail, snow,
thunderstorms, and tornadoes.
Wear and tear is simply the result of abrasion,
physical damage, staining and other symptoms of
continued use. Homeowner habits and lifestyles are
particularly important for this durability factor.
In summary, all houses are under attack by a
mighty and unstoppable foe, namely the forces of
nature, along with kids, pets, and other ìuse condi
tions.î Recognizing this issue is not intended to
signal retreat or resignation, but rather to draw
attention to the need for action.
Of course, actions must be practical in that the
benefits of improved durability should be reasonably
balanced with the costs and efforts of doing so.
Appropriate actions to consider include selecting high
quality material, using appropriate design detailing,
following proper installation procedures, and perform
ing judicious maintenance.
The concept of durability as a function of material
quality is illustrated in Figure 2.2. Note the different
levels of maintenance required to retain acceptable
function of the three hypothetical materials in Figure
2.2. In many cases, however, installation quality may
actually be more important than material quality. In
other cases design decisions can have a profound
effect on making poor quality materials or installations
perform satisfactorily. Proper maintenance and repair
are critical factors in some instances. Usually, all of
these factors are important considerations.
6

Concepts of Durability
Figure 2.1 - The House and the ìDuralogic Cycleî
7

Chapter 2
Figure 2.2 - Loss of Function vs. Time for Three Hypothetical Materials or Products
of Different Quality Levels (poor, acceptable, and best)
Enough said on the concepts, theory, and
philosophy of designing for durability. The next section
reviews some of the most common durability or
performance issues experienced in modern homes,
many of which are addressed in the remaining parts of
this guide.
2.5 Common Durability
Issues
The type and frequency of durability related
problems and general performance problems
experienced in modern homes can be gathered from
various information sources, such as trade organiza
tions, industry surveys, warranty claims, popular
literature, and others. These problems may be related
to design, materials, methods, maintenance, or a
WHAT’S THE COST OF MAINTENANCE?
Most people donít consider long-term
repair and maintenance costs as an
issue in making a home purchase.
However, a typical annual, out-of
pocket (i.e., not including
do-it-yourself tasks) maintenance and
repair expenditure is about $300 to
$600. (Source: NAHB Housing
Economics, Nov 1997. Based on data
from 1995 American Housing Survey).
This amount may actually reflect a
tendency to defer maintenance. Items
like replacing appliances or HVAC
equipment will create even greater
costs as a house becomes older.
combination of these factors. For this reason, this
guide focuses primarily on design issues, but also
has significant content on installation, materials
selection, and maintenance topics as well.
The following summaries, including Tables 2.1
and 2.2, illustrate some commonly reported durability
issues:
Problem Areas in New Construction
ƒ Paints/Caulks/Finishes
ƒ Flooring
ƒ Windows and Skylights
ƒ Doors
ƒ Foundations and Basements
ƒ Siding and Trim
ƒ Structural Sheathing
ƒ Wallboard
ƒ Foundation Insulation and Waterproofing
ƒ Framing
Source: Survey of builders conducted by NAHB Research Center, Upper Marlboro, MD,
January 1992.
Most Frequent House Problems
ƒ Improper Surface Grading/Drainage
ƒ Improper Electrical Wiring
ƒ Roof Damage
ƒ Heating System
ƒ Poor Overall Maintenance
ƒ Structurally-Related Problems
ƒ Plumbing
ƒ Exteriors
ƒ Poor Ventilation
Source: ASHI NEWS Press Release, American Society of Home Inspectors,
Des Plaines, IL, 2000.
8

TABLE 2.1 - TOP FIVE HOMEOWNER WARRANTY CLAIMS
Based on Frequency of Claim Based on Cost of Claim
Gypsum wall board finish Foundation wall
Foundation wall Garage slab
Window/door/skylight Ceramic tiles
Trim and moldings Septic drain field
Window/door/skylight frames Window/door/skylight & other
Mortgage Housing Corporation, Ottawa, Ontario, Canada, November 1994.
Concepts of Durability
action lawsuits in the United States have given
builders and designers some reason to think twice
about specifying new products. Past examples
include:
Source: Defect Prevention Research Project for Part 9 Houses, Ontario Home Warranty Program, Canada
Home Builder and Housing Consumer Product
Problems
1. Foundations and basements ñ Leaks,
construction cost is higher than the
perceived value, difficult to insulate;
2. Paints, caulks, finishes ñ Caulk shrinkage,
premature discoloration and fading, peeling
and blistering, mildew growth, imperfections
of surface, poor coverage;
3. Windows and skylights ñ Air and water
leakage, glass fogs and frosts;
4. Doors ñ Warping, poor weather stripping,
checking and splitting of panels, swelling;
5. Finish flooring ñ Seams visible, damages
easily, inconsistent color, coming up at
edges, poor adhesion;
6. Structural sheathing ñ Excessive swelling,
delamination of sheets;
7. Roofing ñ Leaks, does not seal properly,
wind damage, inconsistent coloration;
8. Siding and trim ñ Siding buckles, nails
bleed, algae grows on it, paint peels,
seams are noticeable, moisture induced
swelling;
9. Wallboard, interior coverings ñ Nail pops,
finish shows seams and/or nail heads;
10. Framing ñ Warped/twisted lumber,
checking/splitting, too many large knots;
11. HVAC Equipment ñ Wrong sizing,

insufficient warm air.

Source: Product Failure Early Warning Program, prepared for NAHB by the NAHB
Research Center, Inc., Upper Marlboro, MD, 1996.
All of these summaries of housing durability
issues point to the previously mentioned problem
areas of installation and material quality, design,
and proper maintenance. And while these perfor
mance problems are not necessarily related to any
specific building product, itís worth mentioning that
builders are generally averse to a certain class of
products ñ those that are ìtoo new.î Major product
and installation failures that have resulted in class
ƒ Exterior Insulated Finish Systems (EIFS);
ƒ Fire-Retardant Treated (FRT) Plywood Roof
Sheathing;
ƒ Certain Composite Sidings and Roofing
Products; and
ƒ Polybutylene Water Piping.
It should be noted, however, that many of these
problems have been resolved by subsequent product
improvements. For example, EIFS systems are now
almost exclusively used with a ìdrainage planeî
system such that any moisture that enters the wall
can escape without harm.
In other cases, products such as polybutylene
piping have been entirely removed from the market.
Although costly examples, these experiences
demonstrate the risk and complexity in the develop
ment and application of new materials and methods of
home construction.
TABLE 2.2 - MAJOR EXPENDITURES FOR REPAIRS,
MAINTENANCE, AND REPLACEMENTS
TO OWNER OCCUPIED HOMES (1998)
Category 1998 Value ($ Millions)
Roofing 8,740
Painting and Papering 8,641
HVAC 5,872
Windows and Doors 5,769
Plumbing 3,368
Siding 1,853
Driveways and walkways 1,138
Flooring 826
Electrical 493
Others (including materials on hand) 10,814
TOTAL 47,514
Source: U.S. Department of Housing and Urban Development.
9

Chapter 2
From a recent pilot study
2
of homes of two
different age groups (1970ís and 1990ís), some
important trends and observations regarding durability
of housing in one locality (Anne Arundel County, MD)
have been identified:
1. The size of roof overhangs decreased
between the 1970s and 1990s.
2. Use of vinyl siding and window frames have
increased dramatically.
3. When present, signs of poor site grading (i.e.,
surface depressions next to house) were
associated with an increased tendency for
foundation cracks.
4. The occurence of wood rot (predominantly
associated with exterior trim) in newer and
older homes was 22 percent and 31 percent,
respectively.
5. Masonry foundations tended to evidence
cracks more frequently than concrete
foundations.
2
Assessing Housing Durability: A Pilot Study, U.S. Department
of Housing and Urban Development, Washington, D.C.,
November 2001
10

CHAPTER 3
Ground and
Surface Water
3.1 General
Nearly all building sites have some potential to
experience problems with ground moisture, particu
larly when the water table is high or drainage is poor.
Poor site drainage and difficult site conditions, such
as ìlooseî soils or fills, can contribute to eventual
building settlement, foundation wall cracking, and
aggravated moisture problems. Years ago, it was
generally much easier to select a suitable building
location on a larger site or to seek alternate sites that
provide better drainage and bearing support
characteristics. However, such a luxury is not easily
afforded in todayís market. Thus, this section gives
recommendations that recognize the need to be
resourceful with the land that is available.
The objective of a foundation is to separate the
building materials and the indoor environment from
the earth while also providing adequate structural
support. The following rules of thumb and recom
mended practices of Section 3.2 should serve to
minimize the potential for durability and performance
problems related to foundations (refer to Section 2.5,
Common Durability Issues).
RULES OF THUMB
ƒMost damp foundations are caused by improper
surface drainage.
ƒWet site ñ ìwaterproofî basement walls per code
and use a sump pump; damp/dry site ñ ìmoisture
proofî basement walls.
ƒDo not build below-ground space below highest
seasonal water table level.
ƒUsing only typical construction practices, as
many as 1 out of 3 basements experience some
form of water problem within the first two years.
ƒWhen in doubt, seek advice from a qualified
geotechnical engineer.
ƒMoisture entering a house through the foundation
will contribute to potential moisture problems in
the above-ground portions of the building, even
the attic through added water vapor loading.
Ground and Sur
face Water
3.2 Recommended
Practices
3.2.1 Recommendation #1:
Preliminary Site Investigation
The following actions may help to identify
potential site problems that can be accounted for in
planning and design. An illustration of a typical bore-
hole used to explore subsurface conditions is shown in
Figure 3.1.
ƒ Survey the surface conditions and local plant
species for signs of seasonal or constant high
ground water levels.
ƒ Consider the lay of the land and surface water
flow onto and off of the site to ensure that
proper surface water drainage can be
achieved around the building site.
ƒ Check soil maps from USDAís Natural
Resources Conservation Service or use a
hand auger to bore one or more test holes at
the proposed building location; and determine
general soil type/characteristics and ascertain
the water table level (be sure to factor in any
seasonal or recent climate conditions such as
the amount of precipitation over the previous
month or so) (see Figure 3.1). At least one
hole should be at the building location and
extend at least a couple of feet below the
proposed footing elevation. If deeper
subsurface problems are expected (as by
local experience), then a geotechnical
engineer may need to use special drilling
equipment to explore deeper below grade to
ensure that adequate support and stability
exists.
11

Chapter 3
Figure 3.1 - Bore Hole Used for Preliminary Site Investigation
ƒ If possible, test the soil for bearing capacity
at the depth and location of proposed
footings. A simple hand-held penetrometer
(e.g., a standardized metal rod and drop
weight) used in accordance with the
manufacturerís instructions serves this
purpose.
ƒ If fill or questionable soil conditions are
suspected (as on a steep slope), the
services of a design professional and
knowledgeable foundation contractor may
be needed to appropriately prepare the site
(e.g., compaction) or design a suitable
foundation system.
ƒ Do not use basement foundations on sites
with high ground water table.
ƒ Avoid silt, heavy clay, or expansive clay
backfill, particularly for basement walls.
Granular soils are preferable.
ƒ Use minimum 3,000 psi concrete in slabs
and foundation walls with welded wire fabric
in slabs and light reinforcement (#3 rebar) in
foundation walls to control cracking, improve
concrete resistance to moisture and
weathering, and improve concrete finishing.
3.2.2 Recommendation #2:
Site Grading and Surface Water
Drainage
Site grading plans should consider the existing
natural water flow and change the water flow to
direct water away from the building foundation,
particularly if the building is located down-slope from
a hill or similar land formation that may produce
significant rainfall runoff. Use of grassy swales is a
common and cost-effective practice when the
potential water volume is not large, wetting is not
constant, and the swale is not sloped steeply enough
to produce high water velocities (see Figure 3.2).
The range of acceptable swale slope depends on
many factors, but slope should not be less than
about 1% to prevent ponding, nor more than about
15% unless rip-rap (4 to 8 inch stone) is used to line
the swale with a filter cloth underlay. The grading
immediately adjacent to the building should be
sloped a minimum of about 4% (or 1/2 inch in 12
inches) for at least 6 feet outward from a building
foundation or as far as practical. If concrete flatwork
(i.e., patio slabs, driveways, and walks) are adjacent
to the building, they should be sloped not less than
2% (about 1/4 inch in 12 inches) away from the
building. Backfill should be tamped firmly to prevent
excessive settlement or the grade should be
adjusted to allow for future backfill settlement. In
addition, gutters and gutter drains should be used to
further remove roof run-off from the foundation area
(See Section 4.2.2).
12

Figure 3.2 - Site Grading and Surface Drainage
Ground and Sur
face Water
3.2.3 Recommendation #3:
Foundation Construction
Foundation options generally include base
ment, slab-on-grade, crawl space, or a mix of
these foundation types (e.g., split level construc
tion). One thing is common in all foundation
construction: ground moisture will find its way ìinî
unless appropriate measures are taken. An
important measure to include is a ground vapor
barrier under all basement, slab-on-grade, or crawl
space construction. This will eliminate (or suitably
minimize) a large potential water vapor source to a
house that can result in or aggravate above-ground
moisture vapor problems (see Chapter 4). The
ground vapor barrier should be placed directly below
and immediately prior to pouring the concrete slab to
avoid damage during construction. Second, some
method of removing ground water from around the
foundation is recommended in all but the driest and
most well-drained site conditions.
Typical basement construction practice and
optional enhancements (i.e., polyethylene sheeting)
for particularly wet sites are illustrated in Figure 3.3.
However, ìwater proofingî is not meant to resist
Figure 3.3 - Basement Construction and Optional Enhancements
for Wet Site Conditions
13

Chapter 3
water from flooding or a high water table. It should be
noted that concrete has a considerably lower vapor
permeability (i.e., can stop water vapor better) than
masonry. However, available data seems to suggest
no significant difference between concrete and
masonry relative to the potential for basement water
problems in actual practice.
For slab-on-grade and crawlspace foundations,
moisture protection usually involves placing the
building on a slight ìmoundî relative to the surround
ing site. The use of a gravel layer under the slab or
on the crawlspace floor is considered optional for
mounded foundations, however, a vapor barrier
should always be used. If the site is properly graded,
a perimeter drain system is unnecessary in mounded
foundation systems.
3.2.4 Recommendation #4:
Frost Protection
Foundations are conventionally protected from
frost (i.e., heave), by placing footings below a locally
prescribed frost depth. An alternative in northern
climates is the Frost Protected Shallow Foundation
technology which offers the benefits of frost protec
tion, energy efficiency, warmer slab edge tempera
tures (reduced condensation potential and improved
comfort), and material savings. This technology
uses the heat generated within a building and
stored in the ground to raise the frost depth around
the structure, allowing for reduced-depth footings.
A typical frost protected shallow foundation detail is
shown in Figure 3.4. The technology and concept
can be used to protect a variety of foundation types
and site structures from frost heave. Refer to
Design Guide for Frost-Protected Shallow
Foundations (NAHB Research Center, 1996) for
additional design and construction guidance.
It should be noted that current building codes
prohibit the use of foundation insulation in areas
with ìheavyî termite infestation probability (i.e.,
southeastern United States). The foam can create
a ìhidden pathwayî for termite access to wood
building materials. Refer to Chapter 6 for methods
to deter termite infestation.
Figure 3.4 - Typical Frost-Protected Shallow Foundation
with Perimeter Drain
14

CHAPTER 4 - Rain

and Water Vapor

4.1 General
The most common and disastrous durability
problems are frequently related to bulk moisture or
rain penetrating a buildingís exterior envelope without
any opportunity to drain or dry out rapidly. If rain
penetration occurs repetitively and continues
undetected or uncorrected, it can cause wood
framing to rot, mold to grow, and steel to corrode.
In fact, particularly bad cases of this type of problem
have resulted in severely rotted wood frame homes
within the period of a couple of years. However, most
rain penetration problems can be isolated to
inadequate detailing around windows and door
openings and similar penetrations through the
building envelope.
The objective of designing a weather barrier
system is pure and simpleñkeep rain water away
from vulnerable structural materials and interior
finishes. Keeping these components dry will maintain
a buildingís structural integrity and help prevent
moisture-related problems like mold. Within this
guide, ìweather barrierî is a general term for a
combination of materials used as a system that
protects the building from external sources of
moisture.
Important related issues are water vapor
diffusion and drying potential. These issues are
considered in tandem since they are practically
inseparable design issues, creating the need to have
an integrated design approach (i.e., one that
adequately considers all factors and their potential
impact on durability).
Some of the information presented in this
chapter is generic in nature and will apply to most
house designs (e.g., overhangs), while other
recommendations are geared more towards specific
configurations like vinyl or wood siding installed over
wood sheathing. The Rules of Thumb listed in the
sidebar to the right and the recommendations in this
chapter should help to address the durability and
performance issues related to liquid moisture (rain),
perhaps the most significant durability factor.
Rain and Water Vapor
4.2 Recommended
Practices
Building walls are subject to water penetration
and repeated wetting depending on their exposure,
the climate, and the integrity of the siding system.
While you canít change the climate in which you
build, it is possible to improve the shielding of walls
and to design walls that are appropriate for ìimper
fectî (i.e., leaky) siding systems.
4.2.1 Recommendation #1:
Roof Overhangs
Figure 4.1 illustrates the frequency of building
walls having moisture penetration problems in a
particularly moist, cool climate (British Columbia) as
a function of roof overhang length. The shielding
effect of roof overhangs is illustrated in Figure 4.2.
Note that a roof overhangís impact will depend on the
climate (Figure 4.3) and type of construction
protected. The potential for wind-driven rain should
also be considered. The climate index map of Figure
4.3 does not directly account for wind-driven rainó
RULES OF THUMB
ƒLiquid water or rain obeys the following rules
with respect to movement:
ƒGravity - water runs downhill
ƒCapillary - water is attracted into small cracks
due to capillary action or surface tension
ƒWind - wind can drive rain into places it
would not otherwise go and create building
interior and exterior pressure differentials that
move it uphill, breaking the first rule (gravity)
ƒNO wall or roof covering is perfectly waterproof,
especially considering that there will be wall
openings, roof penetrations, and other materials
that compromise even the ìwaterproofî
materialsóparticularly in view of the effects of
time.
ƒAvoid depending on caulk as a primary barrier to
moisture penetration (i.e., use flashing).
15

Chapter 4
a condition that varies with local climate or site
exposure. Some important considerations regarding
roof overhangs include:
ƒ Roof overhangs protect exterior walls and
foundations from excessive wetting by rain
wateróthe culprit in many moisture problems
in residential buildings.
ƒ Just as the safety factor is important to
providing for a reasonable structural design
that accounts for foreseen events and
unexpected extremes, so is the roof overhang
to those interested in durable wood-frame
building construction.
ƒ The width of roof overhang to use depends on
a variety of factors, including construction
cost, wall type below, amount of windows and
doors exposed, and the height of the wall.
Recommended overhang widths are provided
in Table 4.1 for typical conditions.
ƒ Greater flexibility in architectural design with
respect to the use (or non-use) of overhangs
for rain water protection is afforded in more
arid climate conditions; in other areas there
are significant durability trade-offs
(see Figure 4.1).
ƒ In moist climates with significant rainfall,
liberal use of overhangs is recommended.
ƒ Roof overhangs also provide durability and
energy benefits in terms of solar radiation
(see Section 5.2).
In Table 4.1, the recommended overhang widths
are given with the assumptions that: all walls have a
properly constructed weather barrier, roofs are
adequately guttered, and normal maintenance of
exterior will occur. For overhangs protecting more
than two-story walls with exposed windows and
doors, larger overhangs should be considered. Rake
(gable end) overhangs also deserve special consid
eration because more costly ìoutriggerî framing
methods will be required for overhangs exceeding
about 12 inches in width and the appearance may
not be acceptable to some home buyers. Also, for
sites subject to frequent wind-driven rain, larger
overhangs and drainage plane techniques that
include an air space behind the siding should be
considered (see Section 4.2.3). For non decay-
resistant wood sidings and trim (as for windows and
door casings), greater overhangs and porch roofs
are recommended.
4.2.2 Recommendation #2:
Roof Gutters and Down-spouts
Properly designed roof gutters reduce the
amount and frequency of roof run-off water that wets
above-grade walls or the foundation. A list of
recommendations and a rule-of-thumb design
approach are presented below to help in the proper
use of gutters. Figure 4.4 illustrates a typical gutter
installation and components.
Figure 4.1 - Frequency of Moisture Problems in Walls of Selected Buildings in a Moist, Cool Climate
(Climate Index of approximately 70 based on Figure 4.3)
Source: Morrison Hershfield Limited, Survey of Building Envelope Failures in the Coastal Climate of British Columbia, Canada Mortgage and Housing Corporation,
Burnaby, BC, Canada, 1996. Figure is based on a selection of 46 buildings of up to eight years old, three to four stories, wood-frame, with various wall claddings. Fifty
percent of walls with problems used direct-applied stucco cladding over building paper and oriented strand board (OSB) wood panels.
16

Climate
Index

Rain and Water Vapor
Source: Modification of Prevention and Control of Decay in Homes by Arthur F. Verrall and Terry L. Amburgey, prepared for
the U.S. Department of Agriculture and U.S. Department of Housing and Urban Development, Washington, DC, 1978.
1
Table based on typical 2-story home with vinyl or similar lap siding. Larger overhangs should be considered for taller
buildings or wall systems susceptible to water penetration and rot.
TABLE 4.1 - RECOMMENDED MINIMUM ROOF OVERHANG WIDTHS FOR
ONE- AND TWO-STORY WOOD FRAME BUILDINGS
1
Climate Index (Figure 4.3) Eave Overhang (Inches) Rake Overhang (Inches)
Less than 20 N/A N/A
21 to 40 12 12
41 to 70 18 12
More than 70 24 or more 12 or more
Figure 4.2 - Roof Overhangs
Figure 4.3 - Climate Index Map Based on Wood Decay Potential
Prepared by the U.S. Weather Bureau.
Source: Theodore C. Scheffer, ìA climate index for estimating potential for decay in wood structures above ground,î
Forest Products Journal, Vol. 21, No. 13, October 1971.
Site specific indices may be
determined using the
following formula, where T is
the monthly mean
temperature (
o
F), D is the
mean number of days in the
month with 0.01 inch or
more of precipitation, and Σ
is the summation of products
(T-35)(D-3) for respective
months of the year.
Climate
Index
NOTE: Roof overhangs also
provide protection from
sunlight; refer to Chapter 5
for advice on using
overhangs to minimize the
impact of UV radiation.
Roof overhangs in
hurricane-prone locales may
require additional anchorage
of the roof.
17

Chapter 4
„ Downspouts that discharge to the surface
should do so at least two feet outward from
the building. Splash blocks or plastic corru
gated pipe are recommended to prevent
erosion and to give further extension of
discharge water away from the foundation,
particularly for downspouts located at inside
corners of buildings.
„ Downspouts that discharge water below
grade should do so into non-perforated
corrugated or smooth plastic pipe. The pipe
should be run underground to a suitable
outfall. Do not connect the gutter drain pipe to
the perforated foundation drain pipe, this
practice will soak the foundation.
„ Gutters and downspouts should be resistant
to corrosion and abrasion from flowing water;
material choices include aluminum (most
popular), vinyl or plastic, copper, and coated
metal (baked enamel or galvanized).
„ Use a gutter splash shield at inside corners
(i.e., valleys) where fast moving water in a
roof valley may ìovershootî the gutter.
„ Gutters, downspouts, and splash blocks must
be cleaned and properly maintained by the
homeowner.
Sizing of Gutters and Downspouts
Generally, a standard 5-inch deep gutter and 2
inch by 3-inch downspouts are adequate for most
homes in most climate conditions in the United
States. However, the following simplified sizing
method may help to avoid problems when unique
situations are encountered. An example is provided
on page 20.
Step 1: Determine the horizontal projected roof
area to be served by the gutter and multiply
by the roof pitch factor from Table 4.2.
Step 2: Estimate the design rainfall intensity (see
map in Figure 4.5).
Step 3: Divide selected gutter capacity (Table
4.3) by the rainfall intensity estimated in Step
2 to determine the maximum roof area
served.
Step 4: Size downspouts and space along gutter
in accordance with factored roof area
calculated in Step 1 for the selected gutter
size and type. As a rule of thumb, one square
inch of down-spout cross section can serve
100 square feet of roof area (i.e.,
2îx3îdownspout for 600 ft
2
; 3îx4î downspout
for 1,200 ft
2
).
(Source: ìAll About Guttersî by Andy Engel, Fine Homebuilding, August/September
1999).
Figure 4.4 - Roof Gutters and Discharge Methods
18

TABLE 4.2 - ROOF PITCH FACTORS
Roof Pitch Factor
Flat to 3:12 1
4:12 to 5:12 1.05
6:12 to 8:12 1.1
9:12 to 11:12 1.2
12:12 1.3
Rain and Water Vapor
TABLE 4.3 - GUTTER CAPACITY (ROOF AREA SERVED IN
SQUARE FEET) BASED ON 1 IN/HR RAINFALL INTENSITY
1
Gutter Shape Gutter Size
5-inch depth 6-inch depth
K-style 5,520 ft
2
7,960 ft
2
Half-round 2,500 ft
2
3,840 ft
2
Note:
1. Values based on a nearly level gutter. Increasing gutter to a slope of 1/16 inch
per foot, multiply values by 1.1 or by 1.3 for 1/8 inch per foot slope.
Figure 4.5 - Rainfall Intensity Map of the United States
4.2.3 Recommendation #3:
Weather Barrier Construction
Weather barrier is a broad term for a combina
tion of materials including siding, roofing, flashing,
sheathing, finishes, drainage plane, and vapor
retarders that, as a system, exhibit water retarding
and vapor retarding characteristics and may also
possess thermal insulation and air infiltration barrier
characteristics.
Drainage Planes
The primary goal in protecting a building wall is
to shield the wall from bulk moisture through the use
of overhangs, gutters, siding, and opening protection
(i.e., flashing or overhangs). As a second line of
defense, a drainage plane provides a way out to
drain any moisture that penetrates the wallís primary
line of defenses (i.e., rain water that gets behind
cladding). In less severe climates (low climate index
- see Figure 4.3) or when a wall is otherwise
protected from rain, the use of a specially detailed
DRAINAGE, VAPOR, AND AIR
Drainage planes do just what their
name impliesó they drain away liquid
water that gets past siding or exterior
cladding. But thatís not all they do.
Drainage planes made from building
paper or housewrap can affect how
water vapor passes (or tries to pass)
through a wall. Table 4.4 gives
recommendations on this. Drainage
planes like housewrap may also serve
as air barriers, a boundary around the
house that reduces air infiltration.
Even if housewrap is only used as an
air barrier to cut down air infiltration,
itís crucial to understand that it will
also collect and channel liquid water
that gets past the wallís claddingólike
it or not. Housewrap
Recommendations (page 25) gives
guidance on this issue.
19

Chapter 4
Step 1 Divide by rainfall intensity as follows: (5,520 ft
2
* in/hr)/(7
Horizontal projected roof area = (14í x 12í) + (14í x 34í) = in/hr) = 788 ft
2
> 708 ft
2
OK
644 ft
2
Therefore, the gutter is capable of serving this area.
Factored area = (1.1)(644 ft
2
) = 708 ft
2
Step 4
Step 2 A single 2î x 3î downspout is not large enough (i.e., 600 ft
2
From rainfall intensity map, Figure 4.5, the estimated < 708 ft
2
). Therefore, use one 3îx 4î downspout (at one of
rainfall intensity is 7 in/hr. the outside corners) or two 2î x 3î downspouts (one at
each outside corner). Be sure the gutter is sloped evenly
Step 3 from near its midpoint toward each downspout so that a
Select a K-style gutter with a 5-inch-depth and a 5,520 ft
2
- nearly equal roof area is served by each.
in/hr rating from Table 4.3.
barrier may have little durability benefit. However, for
wall systems that are not extremely well-protected
from bulk moisture, that are in wind-driven rain
climates, or that are sensitive to wetting, the use of a
secondary drainage plane should be employed.
Figure 4.6 shows a typical wall system with
siding. Itís safe to assume that all types of wall
coverings (siding, brick, masonry) are imperfect and
will leak at some pointó some more than others.
Therefore, it is important to consider the use of a
drainage plane behind the siding material. In some
climates, like arid regions with infrequent rain events,
a drainage plane may be unnecessary or of very little
use. Rain water that does penetrate wood-framed
wall systems in these regions can take advantage of
woodís capacity to temporarily store moisture, and
the wall can dry out via air movement and vapor
diffusion once arid outdoor conditions resume (see
below for more about Drying Potential).
It may be advisable to use an air space between
siding and a drainage plane if:
ƒ A house is in a particularly severe climate
(frequent rainfall or wind-driven rain) such as
coastal regions subject to hurricanes; and
ƒ Moisture-sensitive siding materials (e.g.,
wood) are used.
This air space (e.g., use of furring in Figure 4.6),
in conjunction with vents (and general air leaks) that
allow air to move behind the exterior siding or
cladding, provides pressure equalization and creates
20

a capillary break between the back of the siding and
the drainage plane. These features will help to
reduce the amount of rain water that penetrates
behind the exterior cladding and promote better
drying potential for the siding and the inner wall.
However, creating this space using furring strips
applied on top of the drainage plane material must
account for the effect on details for flashing and
finishing around wall openings such as windows and
doors.
Depending on the wall design approach and the
climate, a drainage plane needs to exhibit certain
characteristics for allowing or retarding the transmis
sion of water vapor, while still rejecting the passage
of liquid water like rain. Table 4.4 provides guidance
in selecting appropriate wall drainage plane charac
teristics for various climates. The table considers
both how well certain materials reject liquid water
and how readily they allow water vapor to pass
through them. This is an important issue that affects
the drying potential of walls.
Rain and Water Vapor
The properties of materials that can be used for
drainage planes are found in Table 4.5. In all
applications, any material used as a drainage plane
should have high resistance to liquid water
penetration.
Vapor Retarders
While itís obvious that the drainage plane of a
wall must be located on the outer face of a wall or
just behind the siding, it is just as important to
remember one rule of thumb related to moisture
vapor transport in walls. Namely, any vapor retarder
must be located on the warm-in-winter side of the
wall (i.e., inside) in all climates except hot/humid
climate where it should be placed on the warm-in
summer side of the wall (i.e., outside) if one is used at all.
Water vapor in the air is transported by vapor
diffusion and bulk air movement. Vapor retarders are
intended to restrict the transmission of water vapor
via diffusion. A common application of a vapor
Figure 4.6 - Weather Barrier Construction
21

Chapter 4
retarder would be the use of a polyethylene sheet or
kraft paper between drywall and framing of exterior
walls in cold climates. However, bulk air movement
(i.e., air leakage containing water vapor) is far more
significant in terms of the amount of water vapor that
can be transmitted, moving roughly 10 to 100 times
more moisture than diffusion. This being said, the
vapor retarder can still play an important role in
controlling the movement of water vapor in walls,
particularly in very cold climates.
Table 4.6 provides guidance on appropriate
locations and characteristics of vapor retarders for
various climates. When using a vapor retarder, it
must be installed on the correct side of the wall or
ceiling. Otherwise, condensation will form and cause
sudden or eventual damage. Also, some older codes
established minimum perm ratios for the inner and
outer faces of a wall (e.g., a minimum outer face to
inner face perm ratio of 5:1 in cold climates to
facilitate drying to the outside). Design rules like this
one point out that many materials can and will
affect vapor diffusion even if they are not classified
as vapor retarders. This point, and the fact that air
movement can also move large amounts of water
vapor, are equally important to designing a wall to
handle water vapor.
Building Paper vs. Housewrap
The question ìshould I use building paper or
housewrapî is often asked. And for certain
climates in Table 4.4, the question remains. This
leads to a discussion of the two product categories
and their relative performance characteristics.
Any discussion of this sort should be prefaced
by recognizing that neither product will work
effectively if not installed correctly ñ and could
even do serious harm to a buildingís durability if
used incorrectly.
TABLE 4.4 - RECOMMENDED DRAINAGE PLANE CHARACTERISTICS

FOR EXTERIOR WALLS IN VARIOUS CLIMATE CONDITIONS

Climate Condition
1
Drainage Plane Characteristic Recommended Product Type
Liquid Water Resistance Water Vapor Permeability
(low = little vapor passes;
high = vapor passes easily)
Hot & Humid High Moderate to Low
2
15# tarred felt
Climate Index >70
HDD < 2,500
Mixed High High to Moderate 15# tarred felt or
Climate Index >20 housewrap
2,500 < HDD < 6,000
Cold High High
3
15# tarred felt or
HDD > 6,000 housewrap
Dry N/A N/A
4
optional
Climate Index < 20
Notes:
1
HDD refers to Heating Degree Days relative to 65œF (see Figure 4.7). See Figure 4.3 for Climate Index.
2
HOT/HUMID CLIMATE CONCERNS: The drying potential of hot/humid climates is through the interior wall, and the layer of lowest vapor permeability (i.e., vapor retarder)
must be located to the outside of the wall. If a drainage plane material is used with a low permeability (i.e., polyethylene sheet or foam panel insulation) then it is imperative
that a high permeability is achieved on the inside face of the wall (which may affect interior finish selection such as paint type and limit use of materials such as wall paper
ñ see Table 4.5 below). In addition, it becomes more important in hot/humid climates to carefully size HVAC systems so that they operate without ìshort cycling.î Again,
moisture entry to the building and condensation potential can be significantly reduced by use of a foundation/ground vapor barrier (Chapter 3).
3
COLD CLIMATE ALTERNATIVES AND CONCERNS: In this case, energy efficiency can be a conflicting objective to the tableís recommendation. For instance, interest in
energy efficiency (or code mandated minimum R-values) often leads builders in cold climates to place an impervious layer of insulation (i.e., polystyrene or foil-faced poly
isocyanurate) on the outer surface of the wall. These materials generally have a low permeability to water vapor (see Table 4.5). Since vapor barriers are often required on
interior (warm-in-winter side) of walls in cold climates, this can create a situation where a wall has low drying potential. Therefore, this approach should be used with
caution in areas that are cold but are also subject to substantial rainfall which may penetrate an improperly installed weather barrier or one that fails to maintain its
resistance to liquid water penetration over time. In addition, it becomes critical to seal key leakage areas judiciously to prevent leakage of moist, warm indoor air into the
wall cavity where it may condense. Condensation in the wall cavity can also be prevented by controlling indoor air humidity. At a minimum, interior moisture sources should
be addressed by using bathroom and kitchen exhaust fans to remove the significant moisture that is produced in these areas of the building. Finally, moisture entering the
building/walls from the ground should be minimized by the use of foundation and ground vapor barriers (see Chapter 3).
4
No drainage plane is required for durability purposes in a dry climate, although care should be taken to seal major air-leakage points for sake of keeping infiltration air out
of wall assemblies.
22

Housewrap products are sometimes viewed
solely as air barriers ñ a product that will reduce air
infiltration and do nothing else. Wrong. As discussed
in Table 4.4, housewrap products also block liquid
water that gets past siding, making this type of
product useful for a drainage plane.
And in fact, housewraps will act to collect and
channel liquid water whether the installer intends for
them to do so or not. This can lead to trouble if
housewrap is installed in a manner (e.g., not lapped
correctly, drains water behind windows) that doesnít
allow for channeling water out of a wall system. So
the lesson is: housewraps are not just air barrier
products, they can ñ and should be ñ used as
drainage planes as well. Their vapor diffusion
characteristics arenít sufficient to allow quick drying
should misinstallation result in bulk water penetra
tion.
Rain and Water Vapor
PLUG UP THE LEAKS
In all cases, major air leakage points
through the building envelope should
be sealed to limit the flow of air, heat,
and moisture. Places to air seal
include areas around door and
window frames, attic hatches,
kneewalls, HVAC chases, and
electrical and plumbing penetrations
into attics.
TABLE 4.5 - DRAINAGE PLANE AND VAPOR RETARDER MATERIAL PROPERTIES
1,2
Material Weight or Thickness Permeance, Perms
3
Liquid Water Loss
5
(vapor retarder = 1 perm or less)
15# asphalt felt 14 lb/100 sf
Dry-cup
Method
Wet-cup
Method
Other
30% 1.0 5.6 ó
15# tar felt 14 lb/100 sf 4.0 18.2
4
ó ó
Building wraps (6 brands) ó 5.0 - 200.0 5.0 - 200.0 ó 0 to 80%
6
Blanket Insul., asphalt coated paper 6.2lb/100 sf 0.4 0.6 - 4.2 ó ó
6mil polyethylene 0.006 in 0.06 ó ó ó
Aluminum foil 0.001 in 0.0 ó ó ó
Gypsum board 3/8 in ó 50.0 ó ó
Plywood (interior glue) 1/4 in ó 1.9 ó ó
Block 8 in ó 2.4 ó ó
Brick 4 in ó 0.8 ó ó
Concrete 4 in ó 0.8 ó ó
Polystyrene, expanded board 1 in 2.0 - 5.8 ó ó
Polystyrene, extruded board 1 in 1.2 ó ó
Vapor retarder paint 0.0031 in ó 0.5 ó ó
Primer sealer paint 0.0012 in ó 6.3 ó ó
Exterior acrylic house and trim paint 0.0017 in ó 5.5 ó ó
Notes:

1
These values only relate to performance in standardized and constant test conditions and do not necessarily represent actual behavior under actual conditions of use.

Leakage as a result of discontinuities and other conditions experienced in construction of buildings may easily alter, by a factor of 2 or more, the overall or localized

performance of a vapor retarder in comparison of these standardized values. Therefore, these values can be used for indexing purposes only.

2
Differences in perm ratings between dry-cup, wet-cup, and other test methods are substantial and any cross comparison should be made on the bases of similar test methods

and conditions. Manufacturer data should be consulted when available.

3
Usually tested according to ASTM E 96.

4
Value can vary to more than 60 perm in 95% relative humidity test conditions.

5
Tested using AATCC 127 test method modified to a 3.5 inch head for 2-hour duration (University of Massachusetts, Building Materials and Wood Technology, Paul Fisette, as

reported on www.umass.edu/bmatwt/weather_barriers.html, October 1999).

6
Of six brands tested, R-Wrap and Tyvek received the best possible rating of 0 water loss (liquid water transmission). However, when these products were subjected to soapy

water and a cedar extractives water solution, the loss rates increased slightly.

23

vapor transmission through the wall (in either
direction). This characteristic is a benefit in hot and
humid regions and in designs where some resis
tance to vapor movement from outside to inside is
desired (e.g. behind brick veneer or unsealed wood
siding). While building paper is not usually viewed as
an air barrier product, it can still be used in conjunc
tion with other measures (e.g. caulk and foam
sealants) to produce a wall system with reduced air
infiltration.
So both products can shed liquid water.
Housewrap tends to be more vapor permeable than
building paper (check the perm rating for specific
brands though), allowing water vapor to diffuse more
easily; but neither product would be considered a
vapor retarder even though both slow the movement
of vapor to some degree. Housewrap can be used as
an air barrier, whereas building paper would likely be
used in tandem with other air sealing measures.
These differences, as well as price, should be the
basis for a choice when a decision needs to be
made. But once more, keep in mind that neither type
of product will perform the way itís supposed to if itís
not properly installed and integrated with flashing of
windows and doors (see Section 4.2.4 on flashing
and housewrap installation).
Housewrap Recommendations
Housewraps are relatively new materials that
serve a dual role as a secondary ìweather resistantî
barrier and an air barrier. However, this dual role of
Rain and Water Vapor
building materials has been known for some time for
materials such as building paper or ìtar paperî
(USDHEW, 1931). Even lath and plaster has been
classified as an effective air barrierña finding that
also stands for its modern day counterpart, gypsum
wallboard. Of course, an air barrier is not a substitute
for proper sealing of penetrations in the building
envelope around windows, doors, utilities, and other
leakage points.
Therefore, as with the application of building
paper, housewraps should be viewed and installed
with the main goal of serving as a secondary
weather-resistant barrier (i.e. drainage plane). Like
tar paper, the edges of housewrap should be lapped
to provide a drainage pathway for water out of the
wall. It is only necessary to tape lapped edges if
some improvement in air-barrier performance is
desired. However, building wraps are not all created
equal in terms of their ìbreathabilityî and this
additional sealing can affect the drying time of the
wall system should it become inadvertently wetted by
condensation or, more importantly, rain water (See
Table 4.5). At wall penetrations, the housewrap
should be properly detailed or flashed (See Section
4.2.4). In some cases, housewraps are installed after
window and door installation (Figure 4.13), and
manufacturer-recommended tapes must be used to
seal the joints. While this practice is not uncommon,
a preferred method is to install the building wrap prior
to window and door installation and to additionally
flash window and door heads as shown in Figure 4.12.
Figure 4.7 - Heating Degree Day (HDD) Map of the United States (65
o
F basis)
25

Chapter 4
Drying Potential
Drying potential, the ability of a wall system to
dry out after it is wetted, is important because it can
compensate for conditions when water gets where
itís not supposed to be. High drying potential will
allow walls that are moist to dry out in a reasonable
amount of time and limit the consequences. An ideal
wall would be one that doesnít let any moisture in
from interior vapor, exterior vapor, rain, snow, or ice.
This would require a hermetically-sealed wall, which
is not practical in residential construction. If this
design approach of a ìperfectî sealed wall is pursued
and water does get into the wall, it will be trapped
there and the results can be disastrous.
Therefore, it is imperative to make less than
ideal materials work satisfactorily through careful
design, careful construction, and an expectation that
water will get into walls. Appropriate solutions will
depend on climate conditions, the building use
conditions, and common sense.
An ideal wall material acts as a storage medium,
safely absorbing excess moisture and expelling it
when the relative humidity decreases during periods
of drying. Heavy masonry walls do this. To some
degree, natural wood materials also exhibit this
characteristic and create a beneficial ìbuffering
effectî to counter periods where moisture would
otherwise accumulate to unacceptable levels.
This effect is part and parcel of the ìbreathing
buildingî design approach and it serves as a safety
factor against moisture problems, just like a roof
overhang.
Materials such as concrete, masonry, and brick
also exhibit a moisture storage or buffering capacity
as do many contents of a home. This creates a lag
effect that should be considered in building design
and operation. For example, moisture levels in
building materials tend to increase during warm
summer months. As the weather cools in the fall, a
moisture surplus exists because the expulsion of
excess moisture lags in comparison to the rate of
change in season temperatures.
Bear in mind that most building moisture
problems are related to exterior moisture or rain.
Moisture vapor and condensation is usually only a
problem in extremely cold climates (upper Midwest
and Alaska) or in extremely hot and humid climates,
particularly when significant moisture sources exist
within a home. For instance, a small house in a cold
climate with high internal moisture loads (people,
bathing, cooking), little natural or mechanical
ventilation, and the lack of a suitable interior vapor
retarder (i.e., between drywall and external wall
framing) will likely experience moisture problems.
4.2.4 Recommendation #4:
Proper Flashing
Flashing is perhaps one of the disappearing
crafts in the world of modern construction and
modern materials that seem to suggest simple
installation, ìno-worryî performance, and low
maintenance. An emphasis on quick installations
often comes at the expense of flashing.
Good flashing installations take time. But itís time
well invested. So, if flashing is to be installed, it is
best to invest the effort to make sure itís done right.
In Figures 4.8 - 4.16 some typical but important
flashing details are provided as models for correct
installation techniques.
RULES OF THUMB AND TIPS
ƒFlashing is necessary for
proper drainage plane
performance in walls
and for roofing systems.
ƒMost leakage problems
are related to improper
or insufficient flashing
details or the absence of
flashing.
ƒAll openings in exterior
walls and roof
penetrations must be
flashed.
ƒCaulks and sealants are
generally not a suitable
substitute for flashing.
ƒWater runs downhill, so
make sure flashing is
appropriately layered
with other flashings or
the drainage plane
material (i.e., tar, felt, or
housewrap).
ƒWater can be forced
uphill by wind, so make
sure that flashings have
recommended width
overlap.
ƒSometimes capillary
action will draw water
into joints between
stepped flashing that is
not sufficiently lapped or
that is placed on a low-
pitch roof ñ take extra
precaution in these
situations.
ƒAvoid joint details that
trap moisture and are

hard to flash.

ƒTreat end joints of
exterior wood trim,
railings, posts, etc. prior
to painting; paint end
joint prior to assembly of
joints; if pre-treating, be
sure the preservative
treatment is approved for
use with the type of paint
or stain being used.
ƒMinimize roof
penetrations by use of
ventless plumbing
techniques, such as air
admittance valves, side
wall vents, and direct
vented appliances (check
with local code authority
for approval).
ƒUse large roof overhangs
and porches,
particularly above walls
with numerous
penetrations or complex
window details.
26

Rain and Water Vapor
BASIC FLASHING MATERIALS
AND TOOLS
ƒFlashing stock (coated aluminum,
copper, lead, rubber, etc.)
ƒ15# felt paper
ƒBituminous adhesive tape
ƒUtility knife
ƒAviator snips or shears
ƒMetal brake (for accurate bending
of custom metal flashing)
Figure 4.8a - Basic Roof Flashing Illustrations
27

Chapter 4
Figure 4.8b - Basic Roof Flashing Illustrations (continued)
NOTES for Figure 4.9:

ï
Extend eave flashing 18 to 24 inches inside the plane of the exterior wall.

ï
Overhang eave flashing 1/4 - inch beyond drip edge flashing.

ï
Apply mastic continuously to joints in eave flashing.

ï
If joints in the eave flashing are not avoidable, locate them over the soffit rather

than the interior area of the building.

Figure 4.9 - Eave Flashing for Preventing Ice Dams
ï
While eave flashing is generally recommended for areas with an average January
temperature less than 25œF, ice dams can be prevented by (1) adequate sealing of
ceilings and tops of interior and exterior walls to prevent warm indoor air from leaking
into the attic space, (2) adequate attic/roof insulation (usually local code requirements
are sufficient) all the way out to the plane of the exterior walls and (3) proper ventilation
through the eave and attic space.
28

Rain and Water Vapor
Figure 4.10 - Window Flashing Illustration
(building wrap installed prior to window; typical nail flange installation)
29

Chapter 4
Figure 4.11 - Window Sill and Jamb Flashing Detail
(building wrap installed after window)
30

Rain and Water Vapor
Figure 4.12 - Window Flashing for Severe Weather
(areas subject to frequent wind-driven rain)
Figure 4.13 - Door and Head Trim Flashing Detail
31

Chapter 4
Figure 4.14 - Deck Ledger Flashing Detail
32

Rain and Water Vapor
Figure 4.15 - Typical Brick Veneer Flashing Details
33

Chapter 4
Figure 4.16 - Brick Veneer Flashing at Roof Intersections
34

4.2.5 Recommendation #5:
Sealants and Caulking
In general, do not depend on sealants and
caulking for long-term service. Using normal quality
caulks and sealants with typical surface preparation,
combined with shrinkage and swelling of building
components, usually results in failure of a water tight
seal within 2 to 3 years or less, particularly on
southern exterior exposures. Nonetheless, there will
be joints and seams that will benefit from appropriate
use and maintenance of caulks and sealants.
Optimally, joints in exterior wood trim or framing
should be simple enough not to trap water and allow
quick drying.
With reasonable adherence to manufacturer
instructions (particularly with respect to surface
preparation and conditions during installation), high
quality caulks and sealants can be made to endure
for a reasonable time (i.e., up to 5 years or consider
ably more when not severely exposed). Some
recommendations regarding selection of quality caulks
and sealants are provided in Table 4.7. In addition,
caulks and sealants should be stored in a warm
environment and should not be stored for more than
a couple of years before use. Finally, the need for
homeowner maintenance and replacement of
caulking must be strongly emphasized.
4.2.6 Recommendation #6:
Roof and Crawl Spaces
To Ventilate or Not to Ventilate
The use of ventilation has been a topic of
confusion for some time. Until recently there has
been little convincing research to confirm traditional
practices or to suggest better ones. To aid in
decisions regarding roof and crawlspace ventilation,
recommendations are provided in Table 4.8 based
on the best information available on the topic. Prior
to use, the reader should consult local building code
requirements and roofing manufacturer warranties to
identify potential conflicts.
Roofs vents (when required) must be installed in
accordance with the local building code or accepted
practice. Plastic vent louvers commonly used on
gable ends must contain UV inhibitors. Vents must
be adequately screened to prevent vermin or insect
entry. In addition, ridge vents (if used) should be
installed and attached to the roof in accordance with
manufacturer recommendations ñ numerous
incidents of improper installation have resulted in
damage during wind events or rain/snow entry to the
roof. Vent area ratios, such as 1 square foot of vent
Rain and Water Vapor
opening for every 300 square feet of attic area refer
to the net vent area, not gross area; so the sizing of
vents must account for obstructions to vents from
louvers and screens.
The roof ventilation recommendations in Table
4.8 are based primarily on durability concerns. These
recommendations are further based on the assump
tion that the following good practices have been
employed:
ƒ All bath and kitchen exhaust fans exhaust
moist indoor air directly to outdoors.
ƒ Indoor relative humidity is kept within
reasonable limits (i.e., 40-60%) and
significant point sources of moisture
(e.g. hot tubs) are controlled
with ventilation.
ƒ Ceiling vapor barriers are used in accordance
with Table 4.6.
ƒ Proper attic insulation levels are installed for
the given climate and location.
While non-vented roof assemblies are a viable
alternative (especially in hot/humid climates),
performance data on such designs over time is still
lacking. Further, the required detailing that goes
along with such a design (e.g., insulation detailing,
controlling surface temperatures in the assembly to
prevent condensation) may be less forgiving than a
traditional ventilation approach in terms of durability.
If a non-vented design is employed, some critical
items to consider include:
ƒ Local building department approval;
ƒ Implications for roofing material warranty;
ƒ All major air leakage points between the living
space and the attic (wire penetrations,
recessed light cans, plumbing lines, HVAC
boots and chases, attic hatches) have been
sealed to limit air leakage; and
ƒ Perimeter wall insulation detailing to satisfy
local fire and insect design requirements.
35

36
T
ABLE 4.7- CAULK CHARACTERISTICS
AND
APPLICA
TION RECOMMENDA
TIONS
1
Chapter 4
Caulk Oil-base Acrylic- latex Butyl rubber Polysulfide rubber Silicone rubber Urethane W
eatherstrip/
caulking cord
Life (yrs) 1-7 2-10 7-10 20+ 20+ 20+ to 20
Best Uses not desirable indoors, protected, or painted narrow openings in wood, metal, glass, masonry anywhere outdoor metal, heat ducts, shallow joints anywhere temporary draft sealing and hole plugging
Adhesion fair-good excellent, except metal very good excellent good, excellent with primer excellent none
Shrink-free poor fair fair excellent excellent excellent excellent
Primer Use
2
porous surfaces porous surfaces for best results none needed special primer on all but metal porous surfaces none needed none needed
Joint T
ype
non-moving to 1/4îw
, 3/4îd
non-moving to 1/4î w non-moving up to 1/4îx1/4î all up to 1/2îx1/2î all from 1/4î d all to 1/4îx1/2î non-moving
T
ack-free (hrs)
2-24 1/4-1/2 1/2-1 1/2 24-72 2-5 4-14 -
Cure (days) to 365 3 7 7 2-5 4-14 none
Clean up with
3
paint thinner water paint thinner
,
naphtha TCE, toluene, MEK paint thinner
,
naphtha, toluol, xylol MEK, acetone, lacquer thinner not sticky
Paint must best best if desired read label if desired no
A
vailable Colors
white, natural, gray white, black, gray
, bronze
white, clear
,
gray
, black,
brown, redwood, beige, bronze, sandstone white, black, gray limestone, bronze, brown white, black, clear
, gray
white, gray
,
black, limestone, bronze; special colors clear
, gray
Source:
Structures and Environment Handbook
, Eleventh Edition (Midwest Plan Service, 1983)

NOTES:
1
Based on advancement in caulk formulation and materials, this table may be in need of revision and may not include newer materi
als.

2
ìPorousî includes wood, wood products, concrete, and brick.

3
MEK = methyl-ethyl-ketone, TCE = trichloroethylene.

For crawlspaces, a non-ventilated crawlspace
design can be employed in all of the climate regions
shown in Table 4.8. A non-ventilated crawlspace
offers benefits in terms of both moisture control and
energy performance. Ventilated crawlspaces,
especially in humid and mixed regions, often
introduce moist outdoor air into a cooler crawlspace
environment. The result is condensation and the
resulting problems like mold and degradation of
building materials. In terms of energy, an
unventilated crawlspace also provides an area for
HVAC equipment and ducts that doesnít present the
temperature swings (and energy penalties) found in
ventilated crawlspaces.
Rain and Water Vapor
Thereís more to it than just taking out the vents
however. The following steps must also be followed
when building a unventilated crawlspace:
ƒ Careful attention to exterior grading
(4% slope minimum);
ƒ Air sealing between outdoors and the
crawlspace area to prevent humid air from
getting into the crawlspace;
ƒ Insulating at the crawlspace perimeter wallsñ
not the floor;
ƒ 6 mil polyethylene groundcover in crawlspace
with joints lapped; and
ƒ Damp-proof foundation wall.
TABLE 4.8 - ROOF AND CRAWL SPACE VENTILATION RECOMMENDATIONS
Climate
3
Attic
1,5
Cathedral Roof
4
Crawl Space
2
Hot/Humid Yes Yes No
Mixed Yes Yes Not Preferred
Cold Yes Yes Optional
Arid (dry) Yes Yes Optional
NOTES:
1
All roof ventilation recommendations are based on the ceiling being sealed at all major air leakage points (i.e., chases,
electric and mechanical penetrations, etc.) and bath and kitchen vent ducts adequately routed to expel air out-of-doors. In
some climates (see Table 4.6), a ceiling vapor retarder (i.e., vapor retarder paint, polyethylene sheet, or asphalt coated
paper) is required in addition to adequate attic/roof insulation.
2
All recommendations are based on properly graded sites and the use of a continuous ground vapor retarder applied to the
foundation area.
3
Climates are defined as in Table 4.4.
4
Cathedral roof ventilation must be continuous along soffit/eave and ridge.
5
Net attic vent area should be 1/300 of attic area and vents shall be continuous along soffit/eave and also located at the
ridge and/or gable ends.
37

Chapter 4
38

CHAPTER 5
Sunlight
5.1 General
Sunlight is made up of visible light and non-
visible radiation such as ultraviolet (UV) and infrared
(IR). Depending on the color and surface character
istics of an object, various wavelengths of solar
radiation may be absorbed, reflected, and emitted
(i.e., ìreleasedî). The more light absorbed and the
less heat capacity (i.e., thermal mass), the greater
the objectís ability to be heated by sunlight. For
example, a dark driveway becomes much hotter on a
sunny day than a light colored concrete sidewalk.
Thus, the sun produces two significant effects that
attack materials and shorten their life-expectancy:
(1)chemical reaction (i.e., breakdown) from
ultraviolet radiation and heat
(2)physical reaction (i.e., expansion and
contraction) from daily temperature cycles
caused by objects absorbing and emitting
heat gained from sunlight.
The chemical and physical reactions caused by
sunlight can cause colors to fade and materials to
become brittle, warp, or crack. Deterioration can
happen relatively quickly (a year or less) or over
longer periods of time depending on the characteris
tics of a material and its chemical composition. In
some cases, materials like plastics that are vulner
able to UV degradation can be made resistant by
adding UV inhibitors to the chemical formulation.
Sunlight
A prime example is vinyl siding. As an alternative
approach, materials can be protected from sunlight
by matter of design (e.g., providing shading or using
reflective coatings).
UV light from the sun is not all bad. For example,
it is UV light that causes a chemical reaction on
special paper that forms the blue lines on blue prints.
However, most everyone has witnessed or experi
enced the painful effects of UV radiation on skin,
which causes sunburn. Consider that the exterior of
a house is like its skin. Therefore, the proper
selection of materials determines to what degree the
building exterior will be able to withstand the
damaging effects of UV radiation. The amount of
solar radiation also varies by geography (see Figure
5.1); the number of cloudless days affects the dose
of UV radiation over the lifetime of a product.
The following section presents a few measures
that can help to counter the effects of solar radiation
on building materials and systems. For homes, some
of the primary problems associated with solar
radiation are color fading, premature asphalt roof
shingle failure, and vinyl siding warping. Excessive
exposure to sunlight will also cause caulk joints to fail
quickly. In addition, when shining through windows,
sunlight can cause interior colors to fade.
Figure 5.1 - Solar Radiation Map of the United States
Source: National Renewable Energy Laboratory
39

Chapter 5
5.2 Recommended
Practices
5.2.1 Recommendation #1:
Overhangs
As with rain on the building envelope, properly
sized roof overhangs can minimize the exposure to
solar radiation and, hence, minimize radiation-related
problems. The width of a roof overhang that will
protect walls from excessive solar exposure in the
summer while allowing heat gain through windows
from winter sunshine depends on where the building
is located with respect to the equator. The sun is
higher overhead in the summer than in the winter. In
addition, for any day of the year, at higher latitudes
the sun is lower in the sky than at lower latitudes.
Therefore, buildings situated farther south receive
greater protection from the summer sun by roof
overhangs, as shown in Figure 5.2.
The solar angle factors of Table 5.1 can be used
to help determine overhang width to achieve the
desired shading effect on south-facing surfaces. An
example calculation shows how the solar angle
factor is used.
TABLE 5.1 - SOLAR ANGLE FACTORS
1
Date
To prevent winter
shading:
Dec 21
Jan 21 and Nov 21
Feb 21 and Oct 21
Mar 21 and Sept 21
To produce summer
shading:
April 21 and Aug 21
May 21 and July 21
June 21
24
1.5
1.2
0.8
0.4
0.2
0.1
0.0
Latitude (degrees North)
32 40
2.0 3.0
1.7 2.4
1.0 1.4
0.6 0.8
0.4 0.5
0.2 0.4
0.1 0.3
48
5.4
3.8
1.9
1.1
0.7
0.5
0.5
Source: Structures and Environment Handbook, Eleventh Edition, Midwest Plan

Service, Iowa State University, Ames, Iowa, 1983.

1
Factors apply for times between 9:00am and 3:00pm for winter shading and at

noon for summer shading. Direct south facing orientation is assumed.

Figure 5.2 - Effect of Building Latitude on Effectiveness of Overhangs
40

EXAMPLE: DETERMINE ROOF OVERHANG WIDTH TO
PROTECT WALL AGAINST SUMMER SUN
Find the overhang length (OL) to shade 6 feet of
wall below the roof overhang for June through
July. Building is located at latitude of 32 degrees
North (consult Atlas for latitude). It is desired to
provide shade for 6 feet of wall below the overhang
at mid-day (i.e., to bottom edge of windows).
Solar Angle Factor (SAF) = 0.2 (for July 21) from
Table 5.1
Wall distance below overhang to shade (WD) = 6
feet
OL = SAF x WD = (0.2)(6 feet) = 1.2 feet
Use a 16-inch (1.33 feet) overhang which will
provide roughly 6 feet 8 inches of shading below
the overhang.
Determine degree of shading in the winter (using
Feb 21) as follows:
WD = OL/SAF = 1.33 feet / 1.0 = 1.33 feet or 16
inches.
The selected overhang width will provide no more
than about 16 inches of shading to the wall during
the main winter months of November through
February. However, some shading to the top few
inches of windows will occur in the early and late
winter months when maximum solar heat gain may
be desirable. But, in this case, the overhang width
should not be decreased in the interest of
maintaining weather protection of the wall.
Sunlight
5.2.2 Recommendation #2:
Light Colored Exterior Finishes
As a second line of defense against damage
from solar radiation, light colored materials and
finishes can be selected. White is excellent and
aluminum, reflective-type coatings are even better.
Light colors can also reduce summertime cooling
load and should reduce energy bills especially in
cooling dominated climates by lowering the solar
heat gain into a building. If properly accounted for in
cooling load calculations, lighter colored roofing may
allow for the use of smaller capacity air conditioning
units. In addition, light colored roof shingles reduce
shingle temperature and, therefore, increase shingle
life. The effect of building exterior color on solar heat
gain is illustrated in Figure 5.3. It is very important,
however, to keep light colored finishes like roofs
relatively clean to take full advantage of their
reflectivity.
5.2.3 Recommendation #3:
UV Protective Glazing
Windows that receive direct sunlight and that are
not treated to block UV radiation will allow sunlight to
enter and fade susceptible materials such as
furniture coverings, carpeting, and drapes. One
solution is to specify interior materials that have UV
inhibitors or that are not susceptible to UV radiation.
Another solution is to specify colors that will not show
fading. However, if these options are not desired or
considered sufficient, there are glazing options for
windows and doors that block UV radiation. These
relatively expensive treatments need only be
specified for south-facing windows.
Figure 5.3 - Effect of Surface Coloration on Solar Heat Gain
41

Chapter 5
5.2.4 Recommendation #4:
UV Resistant Materials
Some materials are naturally UV-resistant, while
others require the addition of UV inhibitors in the
make-up of the material. For example, concrete or
clay tile roofing and Portland Cement stucco or brick
siding are naturally resistant to UV radiation and are
also resistant to temperature effects compared to
other exterior building materials. On the other hand,
plastics are prone to ìdry rotî (embrittlement from
excessive UV exposure) unless UV inhibitors are
provided. Plastics are also prone to significant
expansion and contraction from temperature swings.
Be sure that UV inhibitors are used in materials
that require protection. Many low budget compo
nents, such as some plastic gable end vents, may
also lack UV resistance. All other factors being
equal, choose the material with the best UV resis;
tance if exposure to the sun is a concern.
5.2.4 Recommendation #5:
Landscaping for Shading
Trees planted near a home along the southern
exposure provide shading when most needed
during the day (see Figure 5.4). Also, deciduous
trees, such as maple or oak, should be used so
that winter sun can reach the building. With
appropriate planning, trees can also serve as a
wind break to minimize the effects of wind-driven
rain. Trees should be planted far enough away
from a house to prevent possible damage from
limbs or roots, as well as clogging gutters. Bear in
mind that the greatest amount of solar radiation is
generally received between 9 am and 3 pm.
However, shading of only the late day sun (i.e.,
after 3 pm) is often a preferred and more practical
solution for many sites.
Figure 5.4 - Illustration of Solarscaping
42

Sunlight
EXAMPLE: DETERMINE LOCATION OF SHADE TREE TO PROTECT AGAINST SUMMER SUN
Use the following equation and the solar angle factors (SAF) of Table 5.1 to determine the appropriate location of a maple tree
(mature height of ~60') southward of a building wall (8' height) that is to be shaded during summer months. The building
distance between object obstructing the sun at highest point and item to be shaded
latitude is 40œ North (refer to atlas for site latitude).
where:
d =

h = height of the object obstructing the sun

o
h = height of object to be shaded
s
SAF = solar angle factor (from Table 5.1)
The following values are given:
SAF = 0.4 from Table 5.1 at 40œN latitude for May 21 or July 21
h = 60 feet
o
h = 8 feet
s
Substituting in the equation above,
Therefore, the center of the maple tree should be located about 21 feet southward from the wall or windows to be shaded. Note
that the shading at the first day of summer (June 21) will be slightly less due to the higher solar angle than assumed above. In
addition, the tree should not overhang the building at its mature age. Thus, a distance smaller than about 20 feet is not
recommended and the distance should be increased for trees that are larger at maturity.
43

Chapter 5
44

CHAPTER 6
Insects
6.1 General
Insects are not just nuisances, some are also a
serious threat to building durability. The following
types of insects are known to damage wooden
materials in homes and in other structures:
ƒ Termites,
ƒ Carpenter Ants,
ƒ Wood-boring Beetles, and
ƒ Carpenter Bees.
While all of the above insects can pose a threat
to wood-framed homes, termites are the most
prevalent and damaging insect. Therefore, most of
this chapter addresses issues and practices related
to the control and prevention of termite infestation.
Some of the practices for repelling termites, such as
eliminating hidden areas that termites can travel
through undetected, are also relevant to carpenter
ants. Carpenter ants and wood-boring beetles, like
termites, can be treated chemically with insecticides.
Carpenter bees can be deterred by plugging
entrance holes that commonly occur on wood siding
and soffits.
There are about 56 species of termites in the
United States that can be placed into two groups:
subterranean (ground inhabiting) and non-subterra
nean (wood inhabiting). Subterranean termites are
the most common and are responsible for most
termite damage to wood structures. Therefore, this
chapter focuses on subterranean termites. If non-
subterranean termites are present, special measures
may be necessary to eliminate them. Fortunately,
non-subterranean termites live in much smaller
colonies and are much slower acting than subterra
nean termites.
One variety of the subterranean termite group is
the Formosan termiteñan Asian termite introduced to
the United States following WWII. The Formosan
termite is different from the native subterranean
termite in that it has a much greater colony size and
thus damages wood at a much faster rate. Estimates
state that a colony of Formosan termites will
consume nearly 1,000 pounds of wood per year,
whereas other termite varieties will only eat a few
pounds annually. Formosan termites are also more
likely to survive in a building with minimal ground
contact, even though they require a constant source
of water like other subterranean termites. Formosan
Insects
termites are expanding in range, and are currently
found in the Gulf Coast states and southern states
along the Atlantic coast.
A termite hazard or probability map, shown in
Figure 6.1, is frequently used by building code
authorities, designers, and builders to determine
when certain termite prevention or control methods
should be used. Some building codes may vary in
delineation of the termite probability zones based on
local conditions. The termite hazard map generally
corresponds to the geographic limits of reported
termite damage as shown in Figure 6.2. The
inclusion and degree of termite control and preven
tion used in a building depends on the risk of termite
infestation as defined in Figures 6.1 and 6.2, as well
as local experience.
In summary, termites like to eat wood and they
donít care if itís in your home. In areas subject to
termite infestation, at least one of the practices listed
in Section 6.2 should be used.
6.2 Recommended
Practices
There are basically three techniques for
controlling or preventing termite damage:
ƒ Chemical soil treatment or baits,
ƒ Termite shields, and
ƒ Use of termite resistant building materials.
6.2.1 Recommendation #1:
Chemical Treatment
Types
Chemical treatments for termite control come in
a variety of forms. Generally, chemical treatments for
termites include soil termiticides, termite baits, and
treated wood products. This section will only discuss
soil and bait termiticides.
Chemical soil treatments are designed to form a
protective barrier around a structure to prevent
termites from contacting or penetrating the building.
45

Chapter 6
Figure 6.1 - Termite Probability (Hazard) Map
Figure 6.2 - Extent of Recorded Termite Damage
Source: Wood Handbook, USDA - Forest Products Laboratory, Madison, WI, 2000.
46

Soil treatments are the most common form of
termite control used by the building community.
Commercially, there exist about a dozen soil
treatments that, by various biological means, kill
termites or repel them. Termiticides are generally
preferred over repellents.
Termite baits are encapsulated termiticides
designed to lure insects to the bait, be eaten, and
then killed. The poisons are designed to act slowly
so as to not repel the insect and to facilitate the
consumption and transport of the poison to the nest.
Other termites ingest the termiticide from the insects
that feed directly on the baits through secretions
emitted by the original feeders.
Application
Chemical soil treatments are generally applied
to the soil around the foundation of a home to act as
a shield against termites. The treatments are
performed prior to pouring the slab or foundation,
shortly after foundations and slabs are poured, and
at periodic intervals for the life of the structure.
Directions vary according to the chemical used, but
these locations are of special concern for chemical
application:
ƒ Soil along foundations and crawl spaces;
ƒ Areas of soil disturbance such as bath traps;
ƒ Soil under appurtenances such as attached
slabs and porches;
ƒ Soil in inaccessible or concealed spaces; and
ƒ Soil in proximity to slab or foundation
penetrations due to plumbing, wiring, etc.
Termiticides are applied by one or more of the
following methods: trenching around a foundation
and flooding the trench with a sprayer; inserting a
rod at periodic intervals around a foundation and
injecting the chemical in the soil; and drilling holes in
masonry slab or foundations and injecting the
chemicals into the soil through the holes. Factors
such as access to targeted areas, presence of
landscaping, and the chemical employed dictate the
treatment option used by the pesticide applicator. A
certified pest control operator (PCO) is required for
application of most termiticides.
Performance of termiticides varies considerably
with climate, soil type, structure design, and
homeowner practice. Locations with frequent
precipitation, impermeable or very permeable soils,
or great soil disruption from landscaping activities
will require frequent re-application in order to
maintain termite-resistive properties.
Termite baits are applied to the ground at
intervals around the home as prescribed by the
product label. Some bait systems employ only a
Insects
cellulose bait that requires frequent monitoring. Once
termite activity is detected, a poison is inserted into
the bait housing. Other bait systems contain both
termite lure and poison in one formulation. The key
to satisfactory performance in a bait system is proper
monitoring and placement. Do-it-yourself termite bait
kits are available to the general public, but the
temptation is to purchase too few and monitor the
baits infrequently, thus severely hampering their
effectiveness. Many pest control operators offer bait
systems which better assure proper bait placement
and monitoring.
Re-application and Inspection Services
Chemical termiticides have a limited life because
of leaching or chemical degradation. In addition,
homeowner activities such as disruptive landscaping
tend to limit the effectiveness of chemical treatments.
Therefore, many homeowners opt to employ a
termite service offered by pest control operations.
Typically, a contract with a PCO involves an
initial treatment of the structure with a chemical
termiticide or bait system, followed by an annual
inspection of the structure with periodic retreatment
performed when required. Many PCOís offer
warranties that provide free retreatment if infestation
is detected. Few offer warranties that pay for repair
or replacement of termite-infested materials.
The benefits of an inspection and treatment
service include periodic inspection of a home by
knowledgeable technicians and quick remedial action
when infestation is detected. A client can be better
assured of a competent applicator if the PCO is a
member of the National Pest Management Associa
tion (NPMA). NPMA promulgates the standards that
constitute proper treatment of buildings.
6.2.2 Recommendation #2:
Termite Shield
A termite shield is placed between a masonry
foundation and wood framing to prevent termites
from gaining access to the wood framing compo
nents. Termite shields (Figure 6.3) must be of
termite-resistant materials such as metal or con
crete. Some termites are able to chew through
plastics and thin metals. Also, any seams in a termite
shield must be soldered or otherwise sealed. Since
termite shields require a high degree of care in
installation, they are best used in combination with
soil treatment. They should always be used when
there are potential hidden pathways. Construction
types known to create hidden pathways for termites
47

Chapter 6
include slab-on-grade (except monolithic slabs of
good construction), masonry construction, and brick
veneer construction.
Hidden pathways allow termites access to wood
materials through pathways that cannot be detected
during periodic inspection. When there are no hidden
pathways in construction, subterranean termites can
be easily detected by the presence of shelter tubesó
tunnels that are made of mud to protect them from
light and keep them moist. Because termite shields
are difficult to install on slab-on-grade construction or
split-level construction, other methods of termite
protection (e.g., soil treatment) are generally
preferred for these types of foundations. It is also
noteworthy that termites can gain hidden access
through cracks as small as 1/32-inch wide. There
fore, if concrete is used as a barrier to termites, it
should include welded wire fabric or sufficient
reinforcement to control cracking. Examples of
concrete as a termite barrier are illustrated in
Figure 6.4.
6.2.3 Recommendation #3:
Termite-Resistant Building Materials
Wood can be protected against termite damage
by use of preservative treated wood (e.g., CCA or
Borate). Using treated lumber to frame a home can
add as much as $3,000 to the price of a typical
home. Such a drastic measure, however, is only
used in particularly severe termite hazard areas like
Hawaii.
As an alternative, preservative-treated wood may
be used in isolated locations such as foundation sills
and floor framing directly above the foundation. This
practice is particularly appropriate for crawl space
construction and for basement construction when
ceilings are finished such that these elements are
not easily inspected for infestation. Alternatively,
naturally decay-resistant wood (e.g., heartwood of
redwood and eastern red cedar) may be used, but at
even greater expense than preservative treated
lumber. For this reason, materials such as galva
nized cold-formed steel may be a cost-effective
alternative and are frequently used in Hawaii to
complement or compete with the use of preservative
treated wood. Concrete and masonry building
materials are favored alternatives in areas such as
Florida.
48

Insects
Figure 6.3 - Use of Termite Shields
49

Chapter 6
Figure 6.4 - Use of Concrete as a Termite Barrier
50

CHAPTER 7
Protection
Against Decay
and Corrosion
7.1 General
At a moisture content of greater than 25 percent,
wood is subject to fungal attack or decay. Decay will
be rapid when the temperature is in the range of 70
to 85
o
F. The potential for wood decay when exposed
to the outdoors, therefore, varies in accordance with
climate (refer to Decay Hazard Map, Chapter 4,
Figure 4.3). However, wood exposed to excessive
moisture within any building wall in any climate,
particularly one with a low drying potential (refer to
Chapter 4), will grow mold and rot.
As it is for termites, wood is a food source for
certain molds when conditions are right. Therefore, it
is generally recommended that untreated wood be
maintained in conditions where the moisture content
does not exceed 20 percent.
There are essentially three options for prevent
ing wood decay:
ƒ Protect (or separate) wood from moisture;
ƒ Use naturally decay-resistant wood; or
ƒ Use preservative treated wood.
Of equal concern to the exterior use of wood
material is the corrosion resistance of fasteners that
must hold wood joints firmly together. Finally, it is
important to consider cost-effective alternatives to
wood that offer potential durability and maintenance
benefits. In combination with measures presented
earlier in this guide, particularly Chapter 4, recom
mendations in the following section should address
all of the major concerns regarding durability of wood
construction.
Naturally decay-resistant wood species include
black locust (often used as fence posts) and heart
wood of baldcypress, redwood, and cedar. Due to
cost and scarcity of these wood materials, however,
preservative treated wood is generally the favored
choice unless aesthetics demand otherwise. Of
Protection Against Decayand Corrosion
course, alternatives to wood such as concrete, ma
sonry, or steel construction may also be considered.
7.2 Recommended
Practices
7.2.1 Recommendation #1:
Separation from Ground
One of the oldest and most trustworthy practices
to prevent wood decay is separation from constant
uptake of moisture from the ground. In most normal
outdoor exposures, wood will come to an equilibrium
moisture content of less than 20 percent, although
short periods of greater moisture content can occur.
When enclosed in building construction, the moisture
content of wood will typically reach equilibrium with
the surrounding environment at a moisture content of
8 to 12 percent. However, in constantly damp
locations or in conditions of extremely high humidity,
the moisture content will increase up to the satura
tion moisture content of wood (approximately 30
percent). In most cases, this condition is related to
the lack of adequate separation from ground
moisture. Damp conditions can occur when wood is
in direct contact with the ground or when wicking
through other materials such as concrete or masonry
occurs. Some well-known, code-required details for
separation of wood from ground moisture are shown
in Figure 7.1. If this separation is not possible, and
as a reasonable precaution in all cases, wood sills
and other members in direct contact with the ground
or concrete/masonry near the ground level should be
preservative treated.
51

Chapter 7
7.2.2 Recommendation #2:
Exterior Wood Protective Finishes
Another method for protecting wood from
moisture is to apply a protective wood finish. The
options for exterior wood finishes are wide ranging
and include the following options:
ƒ Natural weathering
ƒ Water repellents
ƒ Water repellent preservatives
(pigmented and non-pigmented)
ƒ Pigmented penetrating stains
(semi-transparent)
ƒ Solid color stains
ƒ Paints
Outside of aesthetic preferences, the choice of
the best finish and its effectiveness will depend on
the type of wood, its surface condition, and the
climate, among other factors. For example, the
smoother a wood surface, the less effectively a finish
will adhere or penetrate. Boards with a vertical or
edge grain (i.e., cut radially across the growth rings
of a log) result in much more durable finishes than
the more common flat grain (i.e., cut tangentially to
the growth rings) for reason of differences in
tendency to shrink, swell, and cup (warp). Edge grain
lumber also weathers better than flat grain. The more
dense a wood is, the less effectively a finish will
adhere or penetrate. Hardwoods often require
special preparation due to pores in the wood. Finish
life is decreased because of high shrink-swell
potential in moist environments. However, in
protected environments (such as interior flooring)
hardwood floors are known for their beauty and
durability. In all cases, the moisture content of the
wood must be sufficiently low (i.e., less than 20
percent) to allow for proper application of a durable
and effective exterior finish. Wood composites
(including veneers such as T1-11) that have the
potential to swell require special protection from
moisture and should not weather naturally.
Exterior wood finishes require vigilant, periodic
maintenance. However, in normal climate conditions,
a good exterior wood paint finish should last up to 10
years and stains for as long as 5 years before
diminished function or appearance. Water repellents
and water repellent preservatives generally require
more frequent retreatment, but the treatment
effectiveness and longevity improves as the wood
weathers and becomes able to absorb more of the
treatment. Penetrating stains also experience this
effect and will increase in effectiveness during the
second and subsequent treatments, with service life
extending to as much as 10 years between treatments.
The most important factors to consider are:
ƒ Choosing the most appropriate and cost-
effective wood material;
Figure 7.1 - Details to Separate Wood from Ground Moisture
52

ƒ Matching the selected wood material with a
compatible finish;
ƒ Applying the finish properly; and
ƒ Educating the owner on the need for periodic
maintenance.
All of these factors will not be very effective
without proper moisture control, particularly for
natural (untreated) wood siding and trim materials.
Refer to Chapter 4 for guidance on measures for
moisture control with specific interest in the use of
weather barrier construction, vapor retarders,
flashing, and overhangs. Overhangs are important in
that they modify the exposure that siding and trim
materials will experience, and enhance the service
life of the finish.
The types of performance problems that may be
experienced with finishes when the above factors are
not appropriately addressed include:
ƒ Moisture penetration
ƒ Mildew
ƒ Wood pigment staining (ìbleed throughî)
ƒ Peeling
ƒ Blistering
ƒ Checking
ƒ Cracking and ìalligatoringî
ƒ Excessive chalking
There are numerous types of paints, stains, and
preservatives with varying cost and performance. It is
beyond the scope of this guide, however, to go into
great detail about the various products. Neither does
this guide address special considerations regarding
the repainting of wood or painting of other materials,
such as galvanized or plain steel. Refer to the
following references for a more detailed treatment of
exterior and interior wood finishing:
ƒ Finishes for Exterior Wood (Forest Products
Laboratory, USDA, 1996); and
ƒ Buildersí Guide to Paints and Coatings (NAHB
Research Center, 1993).
The recommendations given in Table 7.1 are
intended to give the best exterior finish results for
typical conditions and a wide variety of wood
materials commonly encountered in home construc
tion and exterior finishing applications.
Judging Paint Quality
The quality of paint is generally determined by
the following factors and is usually correlated to
price:
ƒ High solids content,
ƒ Low ratio of pigment to vehicle, and
ƒ Type of binder or vehicle.
Unfortunately not all paint labels include the
above information. Therefore, consult a paint
Protection Against Decayand Corrosion
specialist or the manufacturer for additional informa
tion; otherwise, it is generally safe to assume that
cost is directly related to quality. When considering
price, it is important to realize that paints with less
solids content may result in the need for more coats
to provide adequate coverage. Therefore, it is
usually cost-effective to invest in high quality paints.
In general, low gloss or flat paints (high pigment
to vehicle ratio) use more pigment content and are
less durable than gloss paints; and latex acrylic
paints are more flexible and resilient than oil-based
(alkyd) paints. Regardless of the paint selected,
application instructions provided by the manufacturer
should be carefully followed for best results.
Many people falsely believe that painting wood
will stop decay. In fact, painting wood that has
already begun to decay can trap moisture and
promote decay. Paint is primarily used as an
aesthetic finish that also serves to protect wood from
intermittent wetting (as from rain) and weathering
from sunlight (UV radiation). A good quality (mois
ture resistant) paint will help to moderate the
moisture swings through which exterior wood would
otherwise be exposed. If frequent wetting occurs to
painted wood, it may even be more likely to decay
than unpainted wood if not properly maintained,
particularly at end joints of lumber trim, siding, and
window and door casings.
Wood absorbs moisture nearly 30 times more
rapidly through the end grain than through its sides.
If moisture is absorbed, painted wood will tend to dry
slower than unpainted wood and accelerated rotting
can occur near end joints. Therefore, it is always a
good practice to keep joint designs simple and to
pre-treat all end joints with a water repellent
preservative prior to installation and finishing.
53

Chapter 7
TABLE 7.1 - RECOMMENDED FINISHES FOR EXTERIOR WOOD
Wood Material Applications Finish Recommendations Special Enhancements
(Preferred option is bold)
1
Untreated Siding, Trim, Paint: (a)Treat end joints with a
(natural) wood Railings, and Prime all sides with acrylic latex ìstain ìpaintableî water repellent
other items not in blockingî primer preservative; allow 2-3
ground contact Apply two coats of all-acrylic latex house days to dry prior to painting;
paint
4
(b) Top coats and primer
Opaque stain (latex)
5
: should include mildew-cide
Use same procedure for paint (best for
rough surfaces).
Treated wood
2
Decks, Columns, Paint: (a) Treated wood is usually
Framing, Same as above high in moisture; let dry for
Fascia Boards, Trim Opaque stain (latex)
5
: several weeks prior to
Use same procedure for paint; do not use application of finish
on decking (best for rough surfaces) (b) Best if wood is slightly
Semi-transparent stain: weathered for penetrating
Best for wood decks and general use on stain
treated wood; apply two coats
Naturally Siding , Trim, Semi-transparent stain: Painting as for
decay-resistant Decking, Columns, Same as above for treated wood (use non-decay-resistant wood
wood Framing, etc. decay-resistant wood) is also applicable; special
Water-repellent preservative: care should be taken to
Apply two coats; use pigmented version make sure stain blocking
if natural wood color is not desired or use primer is used.
semi-transparent stain for deeper color
modification
Water repellent:
Apply two coats
Wood Composites
3
Siding, Trim Paint: (a) Treatment of end
Same as above for untreated (natural) joints/cuts particularly
wood. important to prevent edge
Opaque (solid color) stains
5
: swelling
Same as above for paint; works best on (b) Penetrating stains and
rough surfaces such as T1-11 siding other ìnaturalî finishes
should not be used
(c) Use of overhangs as
additional protection should
be considered depending
on climate
General Application Recommendations:
ƒ All surfaces should be clean and dry.
ƒ For painted surfaces (including opaque stains) that are very smooth, the surface should be lightly wetted and allowed to dry for several days, then sanded with #50 to #80 grit
sand paper.
ƒ Do not apply paint when temperatures are or will soon drop below 50
o
F or when heavy dew is suspected prior to complete curing. Avoid painting surfaces that will soon become
heated by the sun (i.e., follow the sun around the building).
ƒ Closely follow manufacturer application instructions and coverage recommendations. Coverage is generally around 400 ft
2
per gallon for paint and opaque stains and 200 ft
2
per gallon for penetrating stain. Rougher surfaces will reduce coverage amount per gallon.
ƒ Multiple coats: For penetrating stains, time between coats should allow for drying; for water repellent preservatives, time between coats should not allow drying; for paints, time
between coats should allow 2 days for curing, but not more than 2 weeks.
ƒ Brushed on finishes (especially using back brushing technique) will generally improve finish coverage, penetration, and/or adherence to the wood surface.
ƒ Use corrosion resistant fasteners; deformed shank nails should be considered for siding and trim attachment; stainless steel nails should be considered for natural wood
finishes. Use hot-dipped galvanized nails for treated wood.
ƒ Use of furring behind siding to create an air gap will increase finish and wood siding service life.
NOTES:

1
Based on a subjective consideration of general aesthetics and, primarily, durability relative to other choices.

2
Treated wood refers to wood treated with water-borne preservative such as Copper Chromium Arsenate (CCA). CCA is paintable and stainable and the wood treatment can

actually enhance finish performance provided the wood is dry and the surface is not very smooth or weathered. Weathering, however, does enhance the application of

penetrating stain.

3
Wood composites include OSB, plywood (i.e., T1-11 textured siding panels), and fiber board or hardboard. Follow manufacturer application, installation, and finishing

instructions carefully when using these materials.

4
Paint top coats are generally applied after installation, although the first top coat may be applied prior to installation on all sides, but more importantly the end grain and

exposed sides. Second top coat may be omitted if coverage is sufficient and when used only on sides of the building not facing south or west; however, this may shorten the

expected service life.

5
Opaque stains are not recommended for horizontal surfaces such as trim and window sills, and it is particularly not recommended for wood decking. Opaque stains work best

when applied to rough, un-weathered vertical surfaces.

54

7.2.3 Recommendation #3:
Preservative Treated Wood
Where wood cannot be protected from moisture
or where its service requirements demand resis
tance to constant moisture exposure, preservative
treated wood must be considered for durability
purposes. Untreated wood in ground contact or
exposed to constant moisture in exterior above-
ground applications will rot within a short period of
time, generally less than two years.
The most common wood preservative treatment
is Copper Chromium Arsenate (CCA). In fact, 98%
of all water-born preservatives used to treat wood in
1997 was CCA (source: American Wood-Preserva
tion Association, Wood Preservation Statistics,
1997). CCA, which leaves wood with a light-greenish
tint, has excellent decay resistant qualities when
properly specified. It lasts more than 30 years
without decay in exposure tests when properly
treated. CCA also repels insect infestation. The most
important characteristic for proper treatment is the
amount of chemical that impregnates the wood and
that is retained after treatment. Recommended
retention levels for CCA are given in Table 7.2.
There are several other CCA-like treatments
(e.g., ACQ, boric acid) that require similar levels of
retention for effectiveness. It is also worth noting that
that CCA is not the recommended treatment for
every species of wood. In the west, for instance,
Douglas fir treated with CCA shows poor perfor
mance.
Some pointers to ensure good performance of
treated wood are as follows:
ƒ Allow several weeks for treated lumber to dry
before installation (it is generally wet due to
the water-borne treatment process); if
installed wet, fasten securely to prevent
warping and back-out of fasteners.
ƒ For treated wood that is to be installed
immediately or painted, consider specification
of ìkiln-dried after treatmentî (KDAT) lumber.
ƒ Treat field-cut ends of preservative treated
Protection Against Decayand Corrosion
lumber with an over-the-counter wood
preservative; for thick lumber, preservative
treatment does not penetrate to the middle of
the member.
ƒ Put factory cut and treated ends in the more
severe location (e.g., ends of posts in
ground).
ƒ Use preservative treated lumber that is
labeled and certified by an American Lumber
Standard Committee (ALSC) inspection
agency and that is treated in accordance with
American Wood Preserversí Association
(AWPA) standards.
ƒ Once dry or slightly weathered, treat exposed
wood with a penetrating stain and water-
repellent (unless other finishes are desired).
ƒ Do not use opaque stains or latex paints on
deck surfaces; use only special ìdeckî paint if
solid color is desired.
7.2.4 Recommendation #4:
Fasteners and Corrosion Resistance
Depending on application conditions, there are
several options for fastener selection. Fasteners
used within a buildingís weather barrier are generally
protected from corrosion and, therefore, do not
usually require special consideration regarding
durability. However, in exterior exposures, the
durability of fasteners and metal connectors is a
major issue. The following recommendations are
intended to give reliable, long-term performance:
ƒ Siding nails, as well as nails in treated wood
exterior framing (i.e., decks) should be
galvanized (preferably hot-dipped). Bolts
should also be hot-dipped galvanized rather
than electroplated.
ƒ In particularly severe environments
(e.g., exterior construction subject to salt-
TABLE 7.2 - RECOMMENDED PRESERVATIVE RETENTION LEVELS FOR
CCA-TREATED LUMBER
Application Retention
(lb. per cu. ft. of wood)
Above grade (decking, trim, railings, etc.) 0.25
Ground contact (sills, posts, not in ground) 0.4
Foundations (below ground) 0.6
Marine 2.5
55

Chapter 7
spray from the ocean), stainless steel
fasteners and hardware should be consid
ered, although thicker than normal galvanic
coatings (i.e., G90 or higher) are acceptable.
Situations in which galvanized metal fasten
ers, such as joist hangers, are subjected to
periodic salt deposition without the possibility
of rinsing from rain (e.g., under a deck)
should be avoided.
ƒ Stainless steel siding nails are often used to
prevent rust staining in any environment;
deformed shank siding nails are also prefer
able to prevent nail back-out caused by
moisture cycling of the wood.
ƒ Siding and roofing nails should be installed in
dry wood. Wet wood, when it dries, will lose
some of its holding power on the nail.
Proprietary coatings on pneumatic fasteners are
available and should be used only as recommended
by the manufacturer. These coatings are generally
similar to electroplated galvanic coatings, but special
alloys are sometimes used to enhance corrosion
resistance. Mechanically coated nails are also found
in the market with coating thickness and characteris
tics similar to electroplated galvanic coatings.
Galvanic coating thickness and environmental
conditions are the primary factors in determining the
time until the onset of rust. Service life of nails under
normal exterior conditions is shown in Table 7.3.
Other non-corrosive metals may also be
available for some types of fasteners (e.g., copper or
aluminum). However, aluminum and copper can be
reactive with other metals or environmental condi
tions. For example, aluminum or copper nails should
not be used with galvanized metal connectors. For
best results, fasteners and attached metalic materi
als should always be of the same type of metal.
7.2.5 Recommendation #5:
Alternatives to Wood Exteriors
As a final recommendation to prevent the decay
of exterior wood, there are many new products
available that serve as replacements to wood.
Recently, several engineered wood composites have
been introduced and subsequently encountered
durability failures (see Section 2.5 ñ Common
Performance Problems). This has left many builders
skeptical of engineered wood products for exterior
use. However, with suitable installation and climate
conditions, most engineered wood products have
performed well. Similarly, exterior insulation finish
systems (EIFS) encountered serious problems
related to durability and moisture damage. On the
other hand, some products like vinyl siding and vinyl-
clad or vinyl windows have been used with great
success and increased frequency. Therefore, it is
worthwhile for designers and builders to consider
new materials that offer promise of durability or
affordability, or both. Some of these prducts include:
ƒ Vinyl siding and trim products;
ƒ Vinyl windows and doors;
ƒ Plastic trim products;
ƒ Plastic coated foam, molded plastic, or
fiberglass trim products that are UV-resistant
and that are paintable/stainable;
ƒ Plastic lumber decking and posts;
ƒ Fiber cement siding and trim products; and
ƒ Fiber cement boards, siding, and trim.
Most of these products have been in use for
some time and, if required, include UV inhibitors to
protect against dry rot.
Untreated, non-decay resistant wood species
exposed to the weather (without ground contact or
protective coating) will generally last between 2 and
20 years depending on the severity of the climate
(see Decay Index Map, Figure 4.3). On the other
hand, properly treated or naturally decay-resistant
wood will last more than 20 years without significant
decay, almost regardless of climate.
TABLE 7.3 - NO-RUST SERVICE LIFE OF NAILS EXPOSED TO NORMA
ENVIRONMENT
L OUTDOOR
Nail Type Coating Thickness, mils
(1/1000 of inch)
Galvanized 0.2 (varies)
(electroplated or mechanically plated)
Hot-dipped galvanized 2 to 6
Stainless Steel N/A
Service Life
5 - 10 yrs
20+ yrs
50+ yrs
56

Although many new materials can provide
desirable qualities, an ìold-timerî with a taste for
tradition may desire traditional products. In this case,
the builder or the client must be willing to pay to get
some of the expensive naturally-decay resistant
wood products that are still available, such as
straight grain red cedar or heartwood Douglas fir.
Alternatively, treated wood that can be used with
paints and stains may be selected. Coating
manufacturer recommendations should be carefully
consulted.
The most important concern is to choose
appropriate siding and trim material and detailing for
the climate. In severe climates (e.g., hot and humid),
it may be wise to remain conservative or at least to
run ìfield testî on a shed or some other harmless
application. When experimenting, purchase a
moisture meter and take the time to observe the
performance of the new product as well as some of
your current materials and methods. It is always best
to run ìside-by-sideî comparisons of identical
buildings. Alternatively, you may receive some help in
performing your own tests or certified laboratory tests
by calling the ToolBase Hotline at 800-898-2842 or
sending your request for information to
askanexpert@nahbrc.org. ToolBase is a service of
the NAHB Research Center and is sponsored by
NAHB, CertainTeed, HUD, the North American Steel
Framing Alliance, the Wood Truss Council of
America, the Wood Promotion Network, and others.
Protection Against Decayand Corrosion
57

Chapter 7
58

CHAPTER 8
Natural Hazards
8.1 General
Severe damage to homes is often seen in media
reports following major natural disasters, such as
Hurricane Andrew in Florida and the Northridge
Earthquake in California. As a result, the most
prevalent (and less interesting) forms of damage that
have ìcommon senseî fixes are rarely given the
degree of consideration they deserve.
From past scientific surveys of hurricane
damage, it can be seen that damage to roofing and
water damage to contents are the most frequent and
costly repairs. For example, damage statistics for
Hurricane Andrew and Hurricane Opal (Florida) are
shown in Table 8.1. It can be seen that the most
significant forms of damage were associated with
roofing loss. In Hurricane Andrew, a particularly
severe Category 5 event, roof sheathing loss and
window breakage were also prevalent. Since the
data presented in Table 8.1 was collected using a
random sample of the housing stock in each event,
the findings approximately represent the overall
housing stock performance.
Natural Hazards
Light wood-frame homes are well-known for their
resiliency in earthquake events as evidenced by the
low frequency of collapse, even in extreme earth
quakes. However, because homes are the most
common type of structure, they account for much of
the overall damage, but usually in the form of
cracked interior and exterior finishes. As shown in
Table 8.2, more serious forms of structural damage
to foundations and walls are a relatively rare
occurrence.
Based on the above data, which identifies key
issues related to durability of homes in natural
disasters and places them in the proper perspective,
the following section gives some recommended
practices to improve performance at a modest cost.
Other forms of disaster include wildfires, hail,
tsunamis (tidal waves), etc. For fire resistance, fire
resistant siding and roofing materials as well as
landscaping that reduces fuel sources near to the
home may be used. For hail, resistant roofing
products, such as tile or specially rated asphalt
shingles, may be considered. Properly installed metal
roofing is also a good option for wind, hail, and fire
resistance.
TABLE 8.1 - HURRICANE DAMAGE STATISTICS (SINGLE-FAMILY
HOMES)
Component
Roof sheathing
Walls
Foundation
Roofing
Interior finish
Frequency of Moderate to Severe Damage
(% of all homes)
Hurricane Andrew Hurricane Opal
[165 mph gusts] [100-110 mph gusts]
64%* 2%*
2% 0%
0% 0%
77% 4%
85% Unknown
Sources:
(1) NAHB Research Center, Inc., Assessment of Damage to Single-Family Homes Caused

by Hurricanes Andrew and Iniki, U.S. Department of Housing and Urban Development,

Washington, DC, 1993.

(2) NAHB Research Center, Inc., Assessment of Damage to Homes Caused by Hurricane

Opal, prepared for the Florida State Home Builders Association by the NAHB Research

Center, Inc., Upper Marlboro, MD, 1996.

*Percent value of homes which lost one or more roof sheathing panels.

59

Chapter 8
8.2 Recommended
Practices
Source: NAHB Research Center, Inc., Assessment of Damage to Residential Buildings Caused by the Northridge
Earthquake, prepared for the U.S. Department of Housing and Urban Development, Washington, DC, 1994.
TABLE 8.2 - NORTHRIDGE EARTHQUAKE DAMAGE STATISTICS
(PERCENT OF SINGLE-FAMILY HOMES)
Component No Damage Low Damage Moderate Damage High Damage
Foundation 90.2% 8.0% 0.9% 0.9%
Walls 98.1% 1.9% 0.0% 0.0%
Roof 99.4% 0.6% 0.0% 0.0%
Exterior finish 50.7% 46.1% 2.9% 0.3%
Interior finish 49.8% 46.0% 4.2% 0.0%
8.2.1 Recommendation #1:
Hurricane-Prone Areas
The following recommendations will assist in
improving the durability of homes in areas prone to
frequent high winds resulting from tropical storms or
hurricanes:
ƒ Nail roof sheathing according to
manufacturerís fastening schedule, using
pneumatic or hand driven 8d deformed shank
fasteners or screws.
ƒ Use the ì6-nailî method for attaching 3-tab
roof shingles; make sure the roof deck is dry
prior to installation; follow installation instruc
tions on the packaging.
ƒ Apply roofing cement (mastic) to the under
side of shingle tabs along the roof perimeter
and ridge.
ƒ Use 15# felt roofing underlay and flashings as
shown in Chapter 4.
ƒ Use moderate sloped roofs of 4:12 to 6:12 to
minimize wind uplift while avoiding large
lateral loads on the building; in general, hip
roofs perform better than gable roofs.
ƒ Consider low-profile plans (i.e., a one-story
home is less vulnerable than a two-story
home).
ƒ Use hurricane ties or clips to attach the roof
to the walls; in severe coastal exposures
make sure that the load transfers either
through the sheathing or through additional
brackets down to the foundation; it doesnít
take much effort or hardware to make a big
difference.
ƒ If building on the beach, elevate the house
above the local base flood elevation and set
back as far as possible from the coastline;
expect damage at some point in time ñ
coastal exposures are quite threatening in
hurricane-prone regions.
ƒ Use the services of a knowledgeable design
professional for complex or ìnon-conven
tionalî plans; make sure the detailing is
clearly shown on the plans or construction
shop drawings prior to the start of construc
tion.
8.2.2 Recommendation #2:
Earthquake-Prone Areas
For areas prone to earthquakes, the following
practices may be used to improve durability:
ƒ Use continuous wood structural panel
sheathing on all exterior walls.
ƒ Avoid stucco and similar brittle exterior
finishes (cracks will be apparent and require
repair in moderate to strong events and may
also leak in future rain); however, stucco can
provide a very stiff and strong building that
also minimizes interior finish cracking in
moderate earthquakes.
ƒ Avoid steeply sloped sites or sites with ìsoftî
soils that may liquefy during ground shaking.
ƒ Consider low profile plans (i.e., one-story
instead of two-story home).
ƒ Avoid heavy roofing materials.
ƒ Use the services of a knowledgeable design
professional for complex or non-conventional
plans in hazardous earthquake regions.
60

ƒ Secure heavy equipment such as water
heaters and storage tanks and use flexible
gas lines to natural gas appliances.
ƒ Advise homeowners to secure furnishings,
such as bookshelves and wall hangings, to
prevent damage or injury.
8.2.3 Recommendation #3:
Inspection
Generally, connections are a key area where
wind damage occurs and, to a lesser degree,
earthquake damage in single family homes. Care
should be taken to inspect for the proper connection
of roof and wall sheathing, as well as any required
brackets or metal connectors. In high wind areas,
inspection of roof sheathing nails into a gable end
truss (gable roof) is particularly important. To obtain
thorough inspection, some builders and designers
include special inspection services within the scope
of contracts as a matter of business practice.
Natural Hazards
To assist builders and framers in obtaining the
maximum level of quality possible, the NAHB
Research Center has initiated the Framing Quality
Assurance Program (1-800-638-8556). The program
is ISO 9000 based and requires adoption of effective
quality procedures as well as periodic auditing by a
third party.
8.2.4 Recommendation #4:
Flood-Prone Areas
Flood-prone areas include many coastal zones
subject to storms as well as land near waterways
that periodically experience flooding. A few simple
design considerations for these areas that can
increase house durability include:
ƒ Install components like HVAC blowers,
electrical receptacles, and hot water heaters
at elevated locations in basements. This
practice can make recovery easier and less
hazardous.
ƒ Consider the use of back-flow restriction
valves to reduce the risk of sewer water
backup into houses during flood events.
ƒ Do not build in the 100-yr flood plain or follow
appropriate construction guidelines and
regulations for flood-resistant construction
(i.e., elevated foundation).
ƒ Do not use moisture-sensitive building
materials and finishes below the first above-
grade floor.
61

Chapter 8
62

CHAPTER 9
Miscellaneous
9.1 General
The previous chapters of this book have dealt
with significant durability issues that can impact the
functionality and livability of a home. There are other
durability-related issues in homes that do not
necessarily increase the risk to the structure or the
occupants, but which, nevertheless, are often quite
important to occupants. The presence of these
nuisance items often lends to perceptions of poor
quality and durability. The consumer is no less
concerned with these nuisances than a leaking
window caused by improper flashing or a damp
basement caused by inadequate site drainage.
Nuisances include items such as nail pops or
premature wear of a product or surface. This chapter
focuses on how to address expectations when
dealing with some of the more common problems in
this category.
One of the largest obstacles to overcome is
separating normal wear and tear from premature
wear. As in other parts of the home, this requires
understanding and managing expectations. For
example, carpets, paints and other interior finishes
are generally expected to wear out over time.
Although there are certainly better grades of these
products, they often come with a higher cost. In other
words, consumers need to understand that they
usually ìget what they pay forî when selecting finish
materials. Because there is some amount of
personal choice involved in selecting finish materials,
this document does not attempt to prescribe one type
of product over another. However, where appropri
ate, some options are identified where different types
of finishes may prevent premature wear or prevent
common problems with finishes.
Recommendation #1:
High Traffic Areas
Use wear-resistant surfaces in high traffic areas.
Bathrooms, kitchens, and entryways face more
severe exposure than other areas of the home. Old
standbys like tile, hardwood, and vinyl certainly are
good products for some of these areas. Also
consider some of the new laminates that give the
Miscellaneous
look of wood but which have better resistance to
wear and scratches. A newer trend that appears to
be growing is the use of stained or pigmented
concrete floors.
Recommendation #2:
Finish Selection
Select finishes and colors that can mask dirt in
high traffic areas. In addition to wear in high traffic
areas, keep in mind that darker colors are better at
masking dirt carried in from outside. Although nearly
all carpets today are better at resisting stains,
evidence suggests that lighter colors contribute to
complaints about carpet soiling (see next section).
Recommendation #3:
Carpet Soiling
Carpet soiling is a phenomenon where soils,
combustion particles, and other particulates
accumulate at the base of walls, under interior doors,
and other areas. The result is dark, linear stains
along these surfaces. In the most severe cases, it
cannot be removed by cleaning. Carpet soiling can
be minimized through the use of darker carpet
colors, multiple return-air grilles (as opposed to
central returns), passive returns or jump ducts from
bedrooms, and occupant education about the
implications of using candles in the home.
Recommendation #4:
Stuck Windows
Windows and doors can stick or be difficult to
open and close for a number of reasons. Problems
typically result from the swelling of framing around
openings or excessive deflection in headers.
One way to reduce header deflection is to size
the headers with sufficient stiffness. It is important to
recognize, however, that even with proper sizing,
temporary deflection and even permanent deflection
can occur and possibly interfere with window
operation. A common practice that contributes to
63

Chapter 9
inoperable windows is shimming between the
window frame and the header. This space should be
left open to allow for deflection of the header.
To avoid the swelling of materials and subse
quent problems with the operation of doors and
windows, the entry of water must be prevented by
the use of proper drainage and flashing details. It is
very important to ensure that siding is installed
according to the manufacturerís specifications. Do
not assume that the same details that work with one
type of exterior finish will work with others or that all
windows or doors are the same with respect to the
frameís water tightness.
Finally, when using an air-sealing foam to plug
air leaks around window frames, use low-expansion
foams that donít deflect the frame as they expand
and harden. Non-expanding products, such as caulk
or fiberglass, can be used instead. However, some
window manufacturers void their warranties if such
products are used around their window frames.
Recommendation #5:

Nail Pops and Drywall Cracks

Cracks, visible seams, and nail pops are some
of the most common interior finish complaints lodged
by homeowners. Although it canít be guaranteed that
a home will be immune from these problems, some
strategies can be adopted to minimize their chances
of occurring. One strategy calls for developing
specifications for drywall and framing contractors
that clearly outlines expectations. Another equally
important strategy is follow-up supervision of
contractors. During construction, consider adopting
the following:
ƒ Install finishes only to sufficiently dry lumber
(i.e., 12% moisture content or less) and use a
moisture meter to check conditions.
ƒ Heat homes and keep humidity low to limit
chances that joint compound will cure either
too quickly or slowly and cause seams to
crack.
ƒ Reduce shrinkage that causes nail pops and
cracks by specifying only kiln-dried lumber.
ƒ Hang drywall to minimize joints directly at the
ends or over headers or other openings.
ƒ Consider stiffer floor and ceiling framing to
minimize deflection that can create cracks
along seams.
ƒ Use two-stud corners and drywall clips to
minimize cracks at outside corners.
ƒ When installing drywall on ceilings, float
(i.e., do not fasten) the ends of the sheets at
wall intersections. This will avoid cracking if
the trusses move.
Recommendation #6:
Floor Squeaks
Noisy floors are one of the most common
callback problems for builders. Floors, like other
parts of a home, are subject to movement. The most
typical noise is related to loose nails or other
fasteners that squeak when a person walks across
the floor. Sometimes, noise is the result of move
ment of the floor sheathing when attachment is
insufficient (too few fasteners) or when the sheathing
is not pulled tight to the joist. In other cases,
fasteners that miss the floor joist below and end up
alongside the joist create noise when the joist
deflects and the nail rubs against it. Recommenda
tions include:
ƒ Use only kiln-dried lumber, which is marked
ìKD.î
ƒ Install the correct number, spacing, and type
of fastener into the sheathing. Specify these
items to your trade contractor.
ƒ Consider screws or deformed shank nails as
opposed to smooth shank nails to reduce
movement of the fasteners.
ƒ Consider the use of adhesives to help limit
sheathing movement. Adhesives can stiffen
the floor and reduce bounce. But be carefuló
an adhesive that sets up too soon (e.g., in
cold weather applications) can contribute to
squeaks by preventing the sheathing from
pulling tight to the floor joists.
Recommendation #7:
Subfloor Material
Select subfloor material keeping in mind the
finished floor, the tolerance of the flooring for
unevenness, and the expected weathering that the
subfloor will experience during construction. One
option is to use special moisture-resistant oriented
strand board (OSB) subfloor sheets to reduce edge
swelling when exposure to moisture during construc
tion is unavoidable.
64

Recommendation #8:
Paints and Corners
Consider application-appropriate paints to keep
walls fresh looking. Glossy paints are easier to clean
and should be considered for use on doors, trim, and
other high traffic areas. Flat or matte finishes give a
softer, more appealing texture for interior wall
surfaces while hiding imperfections. Fortunately,
there are now paints on the market that come with a
flat finish but are washable. These make a great
finish in areas such as kitchens, mud rooms,
bathrooms, and childrenís rooms when a flat look is
desired.
Also, consider the durability of wall corners to
reduce dents, chips, and other damage by occupants
by using prefabricated corners to aid in damage
reduction. For more information about available
products, see the PATH website at www.pathnet.org.
9.2 Plumbing
Recommendation #1:
Pipe Material
Choose the right plumbing material for the water
supply and local conditions. In most locations of the
United States, copper and plastic (e.g., CPVC) are
viable products. But sometimes, one is advanta
geous over the other. It is often advisable to check
with local plumbers and code officials to determine if
there is a history of local conditions that would lead
to a preference for a certain material. For example,
are there reports of aggressive soils or water that
may attack the material?
Recommendation # 2:
Washing Machine Leaks
One of the leading causes of insurance claims is
water damage from burst washing machine hoses.
With the trend toward finished basements and the
increasing placement of laundry areas on main floors
and second floors, the potential for damage is
increasing. Simple tools to remind homeowners to
inspect/replace hoses (e.g., magnets with inspection
schedules to fill out) are available. Care should also
be taken to address drainage in case a leak occurs.
A drainage system and catch basin large enough to
accommodate the washing machine and the area
surrounding the hose connection is always recom
mended. When replacement hoses are purchased,
high quality hoses should be selected.
Miscellaneous
Recommendation # 3:
Frozen Pipes
In cold climates, protect water pipes against
freezing. The best approach is to keep all water
pipes within the thermal envelope. This becomes
difficult in vented, unconditioned crawlspaces where
risers may need to be insulated and operable vents
should be closed in the colder periods of the year.
Alternatively, an insulated, unvented crawlspace can
be used (see Section 4.2.6).
Recommendation #4:
Plumbing Units
Select certified kitchen and bath fixtures to
reduce the possibility of premature failure. Tubs,
sinks, shower stalls, and countertops of every type
and grade should meet some minimum standards to
prevent chips, cracks, leaks, or excessive wear and
tear. Look for the NAHB Research Center label or
other label from a reputable quality assurance
agency that lists these products.
Recommendation #5:
Bath Room Design
Consider use of seamless tub and shower units
to reduce reliance on sealants. Inspect for leakage
around bathroom fixtures and replace seals and
sealants as required. Use cement-based backer
board behind tile finishes.
9.3 HVAC
The issues with HVAC systems primarily relate
to comfort, and in a few cases, potential moisture
problems. As a side benefit, actions taken to
address these issues generally tend to improve the
energy efficiency of the home.
Recommendation # 1:
Duct Leakage
Leaky ducts can lead to a host of problems ñ dry
air, humid air, condensation, among others. The
problems that can occur depend on the location of
ducts and the climate. The safest bet is to simply
build tightly sealed duct systems. Tight ducts will
alleviate potential problems and increase the
efficiency of an HVAC system. Designing the home
with the duct system entirely within the thermal
envelope also helps to head off problems.
65

Chapter 9
Recommendation # 2:
House Air Leakage
Keep air infiltration through cracks in the building
envelope to a low level. Like a leaky duct, a leaky
structure also brings in outdoor air and can result in
uncomfortably dry indoor conditions during the
heating season. Air sealing is becoming a more
common component of the energy package for
homes and is an effective practice with or without the
inclusion of a separate air barrier (i.e., building
wrap). But, be aware that an aggressive approach
can make a home too tight, which results in the need
for supplemental ventilation. A blower door test can
be performed to estimate the air infiltration rate.
Recommendation # 3:
Load Sizing
Use proper methods such as Air-Conditioning
Contractorís Association (ACCA) Manual J (software
version is called Right-J) for determining design
heating or cooling loads and HVAC equipment sizes.
Rules of thumb for sizing should not be used.
Bigger is not always better! Oversized equip
ment can lead to moisture problems since the air-
conditioner may not run long enough to adequately
dehumidify indoor air during summer cooling
months.
Recommendation # 4:
Exhaust Ventilation
Use exhaust fans in all full bathrooms and near
other moisture sources in the house, such as kitchen
ranges. With larger floor plans and more interior-
room bathrooms in homes, moisture from showering
has no place to go without an exhaust fan.
Bath fans are often rated for a specific flow at
0.1î water column (wc). This static pressure roughly
correlates to an air grille, five feet of 3-inch flex duct,
and an end point cap. As-built installations are
commonly more extensive than this, and static
pressure levels are greater. Therefore, fans will often
exhaust as little as Ÿ of their rated capacities due to
long duct runs, hoods, and grilles. It is often
advisable to select a fan based on airflow at 0.25î
wc. Rated flow is usually listed on the fan packaging,
or consult manufacturerís literature. Alternatively,
use of a 4-inch or larger diameter fan duct will result
in improved air flow in comparison to standard units
with 3-inch diameter ducting. Also, rigid metal duct is
less restrictive than ìflexî duct.
9.4 Exterior Finishes
Recommendation #1:
Drainage
Provide positive drainage away from patios,
sidewalks, driveways, and other concrete flatwork to
reduce frost heave and other water-related damage.
Drainage starts with a solid base/subgrade and ends
with proper grading at a 2% or greater slope...air
entrained concrete can also help improve durability.
Recommendation # 2:
Siding Installation
Check siding for appropriate installation to avoid
buckling. Vinyl and metal sidings expand and
contract from changes in temperature. Nearly all of
these products should not be nailed or screwed tight
to the structure, but rather, they should be ìhungî
from the nail or screw to allow for movement. It is
also important to leave room where the siding abuts
channels or corner trim. When properly installed,
each piece of siding should be able to move
sideways and up and down slightly.
A problem that commonly occurs with horizontal
siding is buckling at rim joists as a consequence of
shrinkage of the large dimension lumber. To avoid
potential callbacks, consider engineered wood (i.e.,
OSB) for rim joists. If engineered wood rim joists are
used, however, special details for anchoring decks to
the house must be used because the web section of
many engineered wood joists is not suitable for this
purpose.
66

Recommendation # 3:
On-Site Conditions
Protect doors, floor sheathing and other products
against delamination or swelling by keeping them
protected from the elements when stored at the job
site. This practice addresses long-term problems
that are not immediately noticeable, such as slight
bumps in the floor at cut edges of sheathing that
cause increased, localized wear of floor coverings.
Other problems that result from site conditions can
become noticeable very quickly. Examples include
warping of wood products, staining or mold growth,
and weakening of some materials.
The best approach is to minimize exposure of
sensitive products to the elements. Inspect materials
for pre-existing damage when they arrive on site.
Stage construction so that sensitive materials are
covered as soon as possible or provide a dry storage
area for these products.
Miscellaneous
67

Chapter 9
68

Bibliography

General
ASHRAE 1985 Fundamentals Handbook,
American Society of Heating, Refrigeration,
and Air-Conditioning, Inc., Atlanta, GA, 1985.
ASHRAE 1993 Fundamentals Handbook,
American Society of Heating, Refrigeration,
and Air-Conditioning, Inc., Atlanta, GA, 1993.
ASHRAE 1997 Fundamentals Handbook,
American Society of Heating, Refrigeration,
and Air-Conditioning, Inc., Atlanta, GA, 1997.
Structures and Environment Handbook, Eleventh
Edition, Midwest Plan Service, Iowa State
University, Ames, Iowa, 1983.
Residential Structural Design Guide, 2000
Edition, U.S. Department of Housing and
Urban Development, Washington, DC, 2000.
Prevention and Control of Decay in Homes, U.S.
Department of Housing and Urban Develop
ment, Washington, DC, 1978.
Wood-Frame House Construction, Agriculture
Handbook No. 73, U.S. Department of
Agriculture, Forest Service, Forest Products
Laboratory, Madison, WI, revised April 1975.
Caring For Your Home: A Guide to Maintaining
Your Investment, National Association of
Home Builders Home Builder Press, Wash
ington, DC, 1998.
Your New Home and How to Take Care of It,
National Association of Home Builders Home
Builder Press, Washington, DC, 2001.
A Builderís Guide to Marketable, Affordable,
Durable, Entry-Level Homes to Last, U.S.
Department of Housing and Urban Develop
ment, Washington, DC, 1999.
Residential Construction Performance Guide
lines, National Association of Home Builders,
Washington, DC, 2000.
Bibliography and Glossar
y
Foundation/Site (Chapter 3)
Design Guide for Frost-Protected Shallow
Foundations, Sponsored by the U.S.
Department of Housing and Urban Develop
ment and the U.S. Department of Energy,
NAHB Research Center, Inc., Upper
Marlboro, MD, 1996.
Flashing (Chapter 4)
McDaniel, P., ìWrapping the House: Doís &
Doníts,î Journal of Light Construction, March
2000.
Preventing Damage from Ice Dams, Technical
Bulletin (Form No. 215-RR-87), Asphalt
Roofing Manufacturers Association,
Calverton, MD, March 1993.
McCampbell, H., ìTroubleshooting Roof Leaks,î
Journal of Light Construction, October, 1999.
Larson, J. R., ìHow to Avoid Common Flashing
Errors,î Fine Homebuilding, April/May 1998.
Arnold, R. and M. Guertin, ìInstalling Vinyl-Clad
Windows,î Fine Homebuilding, February/
March 2000.
Carrier, J., ìKeeping Water Out of Brick Veneer,î
Journal of Light Construction, November
1999.
SMACNA, Architectural Sheet Metal Manual, 5th
Edition, Sheet Metal and Air Conditioning
Contractors National Association, 1993.
Housewrap (Chapter 4)
Bosack, E. J. and E. F. P. Burnett, The Use of
Housewrap in Walls: Installation, Perfor
mance and Implications, PHRC Report No.
59, The Pennsylvania Housing Research
Center, University Park, PA, December 1998.
69

Bibliography and Glossar
y
Light Frame House Construction, Technical
Information for the use of Apprentice and
Journeyman Carpenters, Vocational Division
Bulletin No.145, U.S. Department of Health,
Education, and Welfare, Washington, DC,
1931 (reprinted 1956).
Ventilation Issues (Chapter 4)
Cushman, T., ìRoof Venting: How Much Is
Enough?,î Journal of Light Construction,
December 1996.
TenWolde, A. and W. B. Rose, ìIssues related to
venting of attics and cathedral ceilings,î
ASHRAE Transactions, V. 105, Pt. 1,
American Society of Heating, Refrigerating
and Air-Conditioning Engineers, Inc., Atlanta,
GA, 1999.
Fugler, D. W., ìConclusions from ten years of
Canadian attic research,î ASHRAE Transac
tions, V. 105, Pt. 1, American Society of
Heating, Refrigerating and Air-Conditioning
Engineers, Inc., Atlanta, GA, 1999.
Recommended Practices for Controlling
Moisture in Crawl Spaces, ASHRAE Techni
cal Data Bulletin, Volume 1Q, Number 3,
American Society of Heating, Refrigerating
and Air-Conditioning Engineers, Inc., Atlanta,
GA, 1999.
Rose, W. B. and A. TenWolde, ìMoisture Control
in Crawl Spaces,î Wood Design Focus,
Forest Products Society, Madison, WI, Winter
1994.
Rose, W. B., ìHeat and moisture performance in
attics and cathedral ceilings,î Wood Design
Focus, Forest Products Society, Madison, WI,
Winter 1994.
Best, Don, ìCrawlspace ventilation update,î
Journal of Light Construction, August 1999.
Insects (Chapter 6)
Wood Handbook ñ Wood as an Engineered
Material, U.S. Department of Agriculture,
Forest Products Laboratory, Madison, WI,
1999.
Design of Wood Frame Structures for Perma
nence, National Forest Products Association,
Washington, DC, 1988.
Manual of Acceptable Practices, Vol. 4, U.S.
Department of Housing and Urban Develop
ment, 1973.
Hu, X.P., D. Ring, A. Morgan, D. Pollet, A Guide
for Integrated Pest Management of Termites,
AgCenter, Louisiana State University, LA.,
2000.
Mankowski, M. and J.J. Morrell, ìIncidence of
Wood-destroying organisms in Oregon
residential structures,î Forest Products
Journal, Vol. 50, No. 1, Forest Products
Society, Madison, WI, January 2000.
Kard, B., ìTermite Control: Results of Testing at
the U.S. Forest Service,î National Pest
Control Association, Dunn Loring, VA,
October 1998.
Kard, B., ìTermiticides ñ The Gulfport Report,î
Pest Control, Advanstar Publications, U.S.A.,
Februrary 1999.
Approved Reference Procedures for Subterra
nean Termite Control, National Pest Control
Association, Dunn Loring, VA, 1991.
70

Decay & Corrosion (Chapter 7)
see General plus:
McDonald, K.A., R.H. Faulk, R.S. Williams, J.E.
Winandy, Wood Decks: Materials, Construc
tion, and Finishing, Forest Products Society,
Madison, WI, 1996.
Micklewright, James T., ìWood Preservation
Statistics 1997,î prepared for the American
Wood-Preserversí Association, Granbury, TX,
1998.
Smulski, Stephen, ìPreservative-treated wood,
lumber that can last a lifetime,î Fine
Homebuilding, No. 63, October/November
1990, pp.61-65.
Baker, A.J., ìCorrosion of nails in CCA- and ACA-
treated wood in two environments,î Forest
Products Journal, Vol. 42, No. 9, September
1992.
Bibliography and Glossar
y
Natural Disasters (Chapter 8)
Assessment of Damage to Single-Family Homes
Caused by Hurricanes Andrew and Iniki, U.S.
Department of Housing and Urban Develop
ment, Washington, DC, 1993.
Assessment of Damage to Homes Caused by
Hurricane Opal, prepared for the Florida
State Home Builders Association by the
NAHB Research Center, Inc., Upper
Marlboro, MD, 1996.
Assessment of Damage to Residential Buildings
Caused by the Northridge Earthquake, U.S.
Department of Housing and Urban Develop
ment, Washington, DC, 1994.
Sciaudone, J., ìNon-Structural Seismic Retrofits
Can Make a Bit Difference,î Building
Standards, Vol. LXIX, No. 6, International
Conference of Building Officials, Whittier, CA,
November-December 2000.
71

Bibliography and Glossar
y
Glossary
Air barrier (also known as air retarder) ñ
material(s) used in design to reduce the flow
of air between indoors and outside. Air
barriers may also serve as drainage planes in
some cases.
Building code ñ a set of building construction
requirements developed by national bodies
which are adopted and administered by local
institutions to certify that buildings (residential
buildings in this case) meet certain minimum
standards for structural integrity, safety, and
durability.
Carpet soiling ñ the discoloration of carpets in
houses due to a combination of conditions
that usually includes airflow under doors or
wall baseplates and a source of dirt, soot, or
airborne particulates.
Damproofing, foundation ñ treatment of
concrete or mortar to retard the passage or
absorption of water, or water vapor, usually by
applying a suitable coating to exposed
surfaces.
Drainage plane ñ the part(s) of a buildingís
weather barrier system that exhibits a high
degree of resistance to liquid water from
outdoors, usually in the form of a water
resistant membrane, layer, or sheet; used in
combination with appropriate for flashing and
sealing details at discontinuities in the wall
assembly (e.g., penetrations for windows,
doors, etc.) or at the drainage plane material
itself (e.g., lap joints between sheets).
Drying potential ñ the ability or capacity of a
material or combinations of materials to dry
once wetted; in residential wall systems this
ability is strongly influenced by the presence
or absence of a vapor retarder(s) and the
driving forces for drying (vapor pressures,
temperature).
Durability ñ the ability of a material, product, or
building to maintain its intended function for its
intended life-expectancy with intended levels
of maintenance in intended conditions of use.
Perm rating (vapor permeance) ñ a measure,
for a given thickness, of a materialís ability to
transmit water vapor (1 perm = 1 gr/h*
ft
2
*in.Hg); a high perm rating indicates that a
material can readily allow water vapor to pass
through it (e.g., gypsum), a low perm rating
indicates that a material will not allow water
vapor to pass (e.g., plastic sheeting)
Sones ñ a unit of sound measurement used in
HVAC applications to rate fan noise; standard
bathroom exhaust fan have ratings of 4
Sones or more.
Swale ñ a stormwater runoff feature formed from
natural materials like soil and vegetation that
collects and channels water runoff; swales
can serve as an alternative to curb and gutter
systems, and allow for some water infiltration
back into the ground instead.
Termite barrier ñ any building material or
component which is impenetrable to termites
and which drives the insect into the open
where its activities can be detected.
Ultraviolet (UV) radiation ñ a form of energy
from the sun in an non-visible wavelength that
can cause chemical reactions in exposed
materials and subsequent fatigue and
discoloration.
Vapor retarder (also known as vapor barrier) ñ
a layer in a building construction (wall, floor,
or roof/ceiling) that restricts the diffusion of
water vapor. The diffusion of water vapor can
be driven by differences in vapor pressure.
Water vapor will be driven from a location of
high vapor pressure (i.e., high humidity) to low
vapor pressure (i.e., low humidity). Typically,
in cold climates the indoor air is at a higher
vapor pressure than the outdoor air that is
dryer and colder. The opposite is true in hot/
humid climates where the lower vapor
pressure is indoors (and is accentuated by
use of air-conditioners and associated
dehumidification). Vapor retarders have a
perm rating of 1 or less.
Waterproofing (foundation) ñ a procedure to
make a material impervious to water or
dampness. The application of a material or
coating to assure water repellency to a
structure or construction unit.
Water vapor diffusion ñ the movement of water
vapor (gaseous water) driven by vapor
pressure differentials.
Weather barrier ñ general term for a combina
tion of materials including siding, roofing,
flashing, sheathing, finishes, drainage plane,
and vapor retarders that, as a system, exhibit
vapor retarding and water retarding character
istics and may also possess thermal insula
tion and air infiltration characteristics.
72

APPENDIX A
Durability
Checklists
Designer’s & Builder’s
Durability Checklist
† Have adequate roof overhangs been specified?
† Does the roof have adequate slope for the roofing
material being used?
† Has valley flashing been adequately detailed?
† Has shading of the building been considered and
planned?
† Have all roofing penetrations been adequately
flashed and detailed?
† Have gutters been sized and specified?
† Has downspout size, location, and outlet point been
detailed?
† Has roof drip edge been specified?
† Has eave ice flashing been specified, if required?
† Has 15# roofing felt been specified?
† Has attic vent location and design been specified?
† Has a secondary drainage plane been specified
where required (building wrap, 15# felt, etc.)?
† Are the drainage plane and flashings at windows
and doors properly detailed?
† Have window head, jamb, and sill flashing details
been specified?
† Have door head flashing details been specified? 

† Has siding corner detail been specified?
† Has air barrier detailing been specified, if needed?
† Has siding selection been specified?
† Have all railing details been specified?
† Has the location and flashing for utility penetrations
been specified?
† Have all bathroom, dryer, and kitchen vents been
specified to be directly vented to the exterior of the
building?
† Does site have adequate slope to remove roof run
off?
† Has adequate foundation backfill material been
specified?
† Are ground clearances between framing, siding,
and ground properly maintained?
† Is treated lumber used where clearances to ground
are not sufficient?
† Is foundation drain specified with proper aggregate
and filter fabric?
Appendices
† Are drainpipes located below the top surface of the
basement slab?
† Is the foundation drainage system properly installed
to provide positive flow of foundation water away
from the building?
† Is foundation drain outlet specified - either through
daylighting or sump pump?
† Are foundation bleed holes specified, if needed?
† Is foundation wall damp proofing or waterproofing
specified as required?
† Are termite protection measures specified?
† Is basement floor gravel layer specified?
† Has crawlspace, slab, or basement floor vapor
barrier been specified?
Homeowner’s Durability
Checklist
† Inspect/replace caulk every 2-3 years.
† Maintain gutters and downspouts in a clean and
operating condition.
† Adjust landscaping sprinklers such that the house
is not accidentally ìwateredî regularly.
† Repaint every 5-7 years.
† Maintain exterior grade near foundation for
drainage away from the house.
† Maintain indoor relative humidity levels below 60%
through the use of the HVAC equipment (heating
during winter, cooling during summer) and auxiliary
dehumidifiers in damp areas like basements.
† Inspect/replace HVAC filter monthly and have an
annual service check on equipment.
† Use exhaust fans whenever showering or generat
ing significant moisture while cooking.
† Do not exhaust clothes dryer to indoors or enclosed
spaces.
† Use unvented combustion appliances only in
accordance with manufacturers recommendations.
† Address all leaks and floods promptly, however
small they may seem.
† Inspect/replace washer hoses periodically.
73

Appendices
APPENDIX B
Estimated Life-
Expectancy of
Building
Materials and
Products
ESTIMATED LIFE EXPECTANCY AND HOMEOWNER MAINTENANCE CHART
Concrete/block foundation
Exposed concrete slabs
Siding (Lifespan depends
on type)
Drywall
Roofing
Gutters and Downspouts
Insulation
Windows
Exterior Doors
Garage Doors
Exterior paints/stains
Wood floors
Carpeting
Building Component
100+
25
10 - 100
30 - 70
15 - 30
30
100+
20 - 50
25 - 50
20 - 50
7 - 10
100+
11
Estimated Life* (years)
Check for cracks or surface deterioration. Consult a
professional if you have any leaking or severe
cracking. Check for termite tubes on foundation.
Inspect for cracking. Seal to prevent water
penetration.
Clean all types of siding. Paint or seal wood siding
(See exterior paints/stains).
Inspect, clean, and paint for aesthetic purposes.
Inspect for missing or deteriorated shingles. Clean to
remove mold buildup.**
Remove debris.
Inspect blown insulation in attic and check floor
insulation (crawlspace) to assure that it is in place.
Inspect and repair weather stripping. Inspect for
broken seals in insulated windows. Clean exterior
window frames.**
Clean and refinish when necessary (See Exterior
paints/stains).
Clean garage door. Lubricate moving parts. Paint or
seal as necessary.**
Clean and inspect. Repaint and caulk as needed.
Clean and wax.
Clean annually.
Homeowner Action
74
*All numbers excerpted and condensed from: NAHB Life Expectancy Survey from ìHousing, Facts, Figures and Trendsî (1997)
**Use care if power washing. The high pressure water can cause more harm than help if not used cautiously.

Appendices
Keep free of debris.
Keep free of debris. Check tank seal and floor wax
collar for leaks.
Clean screen annually. Check for leaking seals.
Keep clear of household items. Have professional
maintenance annually.
Keep free of plants and debris. Cover during winter
months (A/C only). Conduct annual professional
maintenance.
Keep clear of household items. Conduct annual
professional maintenance. Inspect/replace filter
according to manufacturerís recommendations.
Clean condensing coils regularly; allow room behind
and inside appliance for air circulation.
Clean the drain filter regularly.
Clean lint filter regularly. Periodic professional
cleanings will reduce risk of fire.
Keep lint trap free of debris. Clean tank occasionally.
Test and check batteries.
(See termite protection.)
Yearly inspection and retreat as necessary.
5 - 30
50
13 - 20
14
15
18
17
10
14
13
12
100+
5
Sinks
Toilets
Faucets
Water heater
Central air conditioning/
heat pump (outside unit)
Furnace/heat pump
(indoor unit)
Refrigerator
Dishwasher
Clothes Dryer
Clothes Washer
Smoke Detector
Wood Framing
Termite protection
(chemical treatment)
ESTIMATED LIFE EXPECTANCY AND HOMEOWNER MAINTENANCE CHART (CONTINUED)
Building Component Estimated Life* (years) Homeowner Action
*All numbers excerpted and condensed from: NAHB Life Expectancy Survey from ìHousing, Facts, Figures and Trendsî (1997)
**Use care if power washing. The high pressure water can cause more harm than help if not used cautiously.
75

A