Accessory Dwelling Units: Case Study

by HUD, PD&R

U.S
Accessory Dwelling Units: Case Study
. Department of Housing and Urban Development
Office of Policy Development and Research

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Accessory Dwelling Units:

Case Study

Prepared for:

U.S. Department of Housing and Urban Development

Office of Policy Development and Research

Prepared by:

Sage Computing, Inc.

Reston, VA

June 2008

The contents of this report are the views of the contractor and do not necessarily reflect the views or policies of
the U.S. Department of Housing and Urban Development or the U.S. Government.

Table of Contents

Introduction....................................................................................................1

History of ADUs............................................................................................1

Types of Accessory Dwelling Units...........................................................2

Benefits of Accessory Dwelling Units.......................................................2

Examples of ADU Ordinances and Programs.........................................3

Conclusion......................................................................................................7

Appendix A..................................................................................................A-1

Appendix B..................................................................................................B-1

Appendix C.................................................................................................C-1

Appendix D.................................................................................................D-1

Appendix E..................................................................................................E-1

Appendix F...................................................................................................F-1

iii

Accessory Dwelling Units: Case Study

Introduction
Accessory dwelling units (ADUs) — also referred to
as accessory apartments, second units, or granny flats
— are additional living quarters on single-family lots that
are independent of the primary dwelling unit. The sepa-
rate living spaces are equipped with kitchen and bath-
room facilities, and can be either attached or detached
from the main residence.
1
This case study explores how
the adoption of ordinances, with reduced regulatory
restrictions to encourage ADUs, can be advantageous
for communities. Following an explanation of the various
types of ADUs and their benefits, this case study
provides examples of municipalities with successful
ADU legislation and programs.
History of ADUs
Development of accessory dwelling units can be traced
back to the early twentieth century, when they were a
common feature in single-family housing.
2
After World
War II, an increased demand for housing led to a boom-
ing suburban population. Characterized by large lots
and an emphasis on the nuclear family, suburban devel-
opment conformed to Euclidean-type zoning codes, a
system of land-use regulations that segregate districts
according to use.
3
Suburbs continued to be a prevalent form of housing
development throughout the 1950s and 1960s. The rapid
growth of suburbs reinforced the high demand for
lower-density development, and ultimately led most
local jurisdictions to prohibit ADU construction. In spite
of zoning restrictions, illegal construction of ADUs con-
tinued in communities where the existing housing stock
was not meeting demand; San Francisco was one such
community. During World War II, the Bay Area experi-
enced a defense boom that created a high demand for
workforce housing, resulting in a large number of
illegally constructed second units. By 1960, San Francisco
housed between 20,000 to 30,000 secondary units, 90
percent of which were built illegally.
4
In response to suburban sprawl, increased traffic con-
gestion, restrictive zoning, and the affordable housing
shortage, community leaders began advocating a change
from the sprawling development pattern of suburban
design to a more traditional style of planning. Urban
design movements, such as Smart Growth and New
Urbanism, emerged in the 1990s to limit automobile
dependency and improve the quality of life by creat-
ing inclusive communities that provide a wide range of
housing choices. Both design theories focus on reform-
ing planning practices to create housing development
that is high density, transit-oriented, mixed-use, and
mixed-income through redevelopment and infill efforts.
5
In the late 1970s to the 1990s, some municipalities
adopted ADU programs to permit the use and construc-
tion of accessory units. Many of these programs were
not very successful, as they lacked flexibility and scope.
Although a number of communities still restrict devel-
opment of accessory dwelling units, there is a growing
awareness and acceptance of ADUs as an inexpensive
way to increase the affordable housing supply and
address illegal units already in existence.
Interior ADU – located in attic space
Photo credit: Town of Barnstable, Massachusetts
1
Municipal Research and Services Center of Washington, Accessory Dwelling Units, October 1995, http://www.mrsc.org/Publications/textadu.

aspx#tenant.

2
Transportation and Land Use Coalition, Accessory Dwelling Units, http://www.transcoalition.org/ia/acssdwel/01.html#body.

3
Transportation Research Board, The Costs of Sprawl Revisited, 1998, http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_rpt_39-a.pdf.

4
San Francisco Planning and Urban Research Association, Secondary Units: A Painless Way to Increase the Supply of Housing, August 2001,

http://www.spur.org/newsletters/0801.pdf.

5
New Urban News, The New Urbansim – An alternative to modern, automobile-oriented planning and development, July 2004,

http://www.newurbannews.com/AboutNewUrbanism.html.

1

Types of Accessory Dwelling Units
Depending on their location relative to the primary dwell-
ing unit, ADUs can be classified into three categories: in-
terior, attached, and detached.
6
Interior ADUs are located
within the primary dwelling, and are typically built through
conversion of existing space, such as an attic or basement.
Attached ADUs are living spaces that are added on to the
primary dwelling. The additional unit can be located to the
side or rear of the primary structure, but can also be con-
structed on top of an attached garage. Detached ADUs are
structurally separate from the primary dwelling. They can
be constructed over existing accessory structures, such
as a detached garage, or they can be built as units that are
separate from accessory and residential structures.
Benefits of Accessory Dwelling Units
Accessory dwelling units offer a variety of benefits to com-
munities. They help increase a community’s housing supply,
and since they cost less than a new single-family home on
a separate lot, they are an affordable housing option for
many low- and moderate-income residents.
7
Elderly and/or
disabled persons who may want to live close to family
members or caregivers, empty nesters, and young adults
just entering the workforce find ADUs convenient and
affordable.
8
In addition to increasing the supply of afford-
able housing, ADUs benefit homeowners by providing
extra income that can assist in mitigating increases in the
cost of living.
Accessory dwelling units have other advantages as well.
They can be designed to blend in with the surrounding
architecture, maintaining compatibility with established
neighborhoods and preserving community character.
Furthermore, there is no need to develop new infrastruc-
ture, since ADUs can be connected to the existing utilities
of a primary dwelling. Allowing ADUs facilitates efficient
use of existing housing stock, helps meet the demand for
housing, and offers an alternative to major zoning changes
that can significantly alter neighborhoods.
9
ADU attached to the side of a garage addition
Illustration: RACESTUDIO and city of Santa Cruz
Attached ADU
Photo credit: http://mass.gov
Detached two-story ADU over garage
Illustration: RACESTUDIO and city of Santa Cruz
6
Transportation and Land Use Coalition.

7
Atlanta Regional Commission, Accessory Dwelling Units, August 2007, http://www.atlantaregional.com/documents/

Accessory_Dwelling_Units_.pdf.

8
Ibid.

9
Municipal Research and Services Center of Washington.

2

Examples of ADU
Ordinances and Programs
The following section of the case study provides an
overview of ADU ordinances that have been adopted by
five communities from across the nation. To gain a wider
understanding of ADU programs in practice, the five com-
munities have been chosen to represent a diverse range of
geographic, demographic, and socioeconomic characteris-
tics with different land use and growth control policies.
Lexington, Massachusetts
Lexington, Massachusetts is an affluent historic town,
located 11 miles northwest of Boston, with a population
of 30,355.
10
According to the town’s 2002 Comprehensive
Plan, Lexington has largely exhausted its vacant unpro-
tected land supply and is a highly built-out suburb with less
than 1,000 acres of land available for new development.
11
Approximately 18 percent of the households in Lexington
are eligible for affordable housing of some sort, and with a
median home sales price of over $600,000, many residents
are being priced out of the housing market.
12
This limited
growth potential and strong demand for affordable housing
has led to the adoption of accessory apartment programs.
The town implemented its first accessory unit bylaw in
1983, resulting in the construction of 60 units. In February
of 2005, Lexington amended its bylaws to improve the
clarity and flexibility of its ADU program.
13
The town
affirmed that the purpose of promoting ADUs is to
increase the range of housing choices, encourage popula-
tion diversity, and promote efficient use of the housing
supply while maintaining the town’s character.
The amended bylaws reduce or eliminate minimum lot
size requirements, allow ADUs ‘by-right’ in homes built as
recently as five years ago, and allow second units by special
permit in new construction, or as apartments in accessory
structures. The Lexington Zoning Code allows two ADUs
per lot, provided the primary dwelling is connected to
public water and sewer systems.
14
Provisions allow absen-
tee ownership for two years under special circumstances.
In addition, a minimum of one off-street parking space
must be provided for every accessory unit. The by-right
accessory apartments must be located within the primary
dwelling and are allowed on lots that are at least 10,000
square feet. The maximum gross floor area of a by-right
accessory apartment is 1,000 square feet and the unit
cannot have more than two bedrooms.
15
Increased flexibility in the program has proven beneficial
to Lexington in the development of ADUs. According to
Aaron Henry, Senior Planner for Lexington, the town’s
Housing Partnership Board is launching an education and
outreach campaign for their ADU program to raise public
interest.
Santa Cruz, California
Santa Cruz, California is a seaside city with a population of
54,600; it is one of the most expensive cities in the country
in which to live. In 2006, the median price for a single-
family home in Santa Cruz was $746,000, which only 6.9
percent of the city residents could easily afford.
16
In spite
of the high cost of living, the city continues to be a desir-
able destination on account of its scenic location and prox-
imity to San Francisco and the Silicon Valley. The location
of a campus of the University of California — the area’s
largest employer — also adds to the demand for housing
in Santa Cruz.
17
Another contributing factor is the limited
amount of land allowed for development within the city’s
Detached ADU over garage – design by Boone/Low
Architects and Planners
Illustration: RACESTUDIO and city of Santa Cruz
10
U.S. Census 2000, www.census.gov.

11
Town of Lexington, Comprehensive Plan, 2002, http://ci.lexington.ma.us/Planning/CompPlan.htm.

12
Town of Lexington, Lexington Housing Strategy, October 2007, http://ci.lexington.ma.us/Planning/Documents/

Housing%20Strategy%20(Oct%202007).pdf.

13
The Massachusetts Smart Growth/Smart Energy Toolkit, Accessory Dwelling Units (ADU) Suburban Case Study, http://www.mass.gov/envir/

smart_growth_toolkit/pages/CS-adu-lexington.html.

14
See Appendix A.

15
Town of Lexington, http://ci.lexington.ma.us.

16
City of Santa Cruz, http://www.ci.santa-cruz.ca.us.

17
Fred Bernstein, Granny Flats for Cool Grannies, February 2005, http://www.fredbernstein.com/articles/display.asp?id=91.

3

greenbelt. In order to preserve the greenbelt while accom-
modating new growth, promoting public transportation,
and increasing the supply of affordable housing, the city
adopted a new ADU ordinance in 2003.
Prototype site layout for attached ADU – ADU Manual
Illustration: RACESTUDIO and city of Santa Cruz
This ordinance sets forth regulations for the location,
permit process, deed restrictions, zoning incentives, and
design and development standards for ADUs. Accessory
dwelling units are permitted in designated residential zones
on lots that are at least 5,000 square feet in area. No more
than one ADU per lot is allowed and the property owner
must occupy the primary or accessory dwelling unit. ADUs
that do not meet the permitting requirements stipulated
in the ordinance must undergo a public hearing process.
Development fees are waived for ADUs made available for
low- and very-low-income households.
18
ADU Permits approved for the city of Santa Cruz
Source: City of Santa Cruz
In addition to the ordinance that regulates the develop-
ment of ADUs, Santa Cruz has established an ADU devel-
opment program with three major components: technical
assistance, a wage subsidy and apprentice program, and
an ADU loan program.
19
As part of the technical assistance
program, the city published an ADU Plan Sets Book that
contains design concepts developed by local and regional
architects. Homeowners can select one of these designs
and receive permits in an expedited manner. In addition,
the city offers an ADU Manual, which provides homeown-
ers with information on making their ADU architecturally
compatible with their neighborhood, zoning regulations
relevant to ADUs, and the permitting process.
Santa Cruz’s ADU Development Program has won numer-
ous awards and has been used as a model by other
communities. According to Carol Berg, who is the housing
and community development manager for the city, an aver-
age of 40 to 50 ADU permits have been approved every
year since the start of the program. She attributes the
program’s success primarily to zoning changes that were
adopted to facilitate development of ADUs, such as the
elimination of covered parking requirements.
Portland, Oregon
With a population of approximately 530,000, Portland
is the most populous city in the state of Oregon, and is
noted for its strong land use control and growth manage-
ment policies. Although Portland has had an ADU program
in place for several years, ADU development was not
effectively promoted until 1998, when the city amended
its laws to relax the regulations governing ADUs.
20
The
amendments eliminated the minimum square footage and
owner-occupancy requirements. ADUs are now allowed in
all residential zones with relaxed development standards.
Portland’s regulations permit the construction of ADUs on
lots with a single-family home, as long as they are smaller,
supplementary to the primary residence, and no more
than 800 square feet.
21
They can be created by conver-
sion of an existing structure or by construction of a new
building. An early assistance process is available to help
with project development for ADUs created through the
conversion of an existing structure. ADUs that meet all the
standards are permitted by right and do not require a land
use review. No additional parking is required for accessory
18
See Appendix B.
19
City of Santa Cruz, Accessory Dwelling Unit Development Program, http://www.ci.santa-cruz.ca.us.

20
Barbara Sack, city of Portland.

21
See Appendix C.

4

units. Portland’s ADU program guide outlines ways to bring
existing nonconforming units into compliance.
The city considers ADUs to be more affordable than other
housing types because of the efficiency of the units in using
fewer resources and reducing housing costs. City planner
Mark Bello notes that allowing more ADUs did increase
the housing supply, and that city residents viewed ADUs
positively and were satisfied with the changes made. He
also added, “There were no significant negative issues that
arose from liberalizing Portland’s code.”
Barnstable, Massachusetts
With seven villages within its boundaries and a total
population of 47,821, the town of Barnstable is the
largest community in both land area and population on
Cape Cod.
22
Approved in November 2000, Barnstable’s
Accessory Affordable Apartment or Amnesty Program is a
component of its Affordable Housing Plan.
23
The program
guides creation of affordable units within existing detached
structures or new affordable units within attached struc-
tures. Eligibility for the program is limited to single-family
properties that are owner-occupied and multifamily prop-
erties that are legally permitted.
Barnstable’s amnesty program is seen as a way to bring
the high number of existing illegal ADUs into compliance
with current requirements. In order to bring a unit into
compliance, the property owner must agree to rent to
low-income tenants — those earning 80 percent or less
ADU over detached garage
Photo credit: Town of Barnstable
ADU on lower level of primary dwelling
Photo credit: Town of Barnstable
of the area median income — with a minimum lease term
of one year. The amnesty program offers fee waivers for
inspection and monitoring of units and designates town
staff to assist homeowners through the program’s admin-
istrative process. The town can access Community Devel-
opment Block Grant funds to reimburse homeowners for
eligible costs associated with the rehabilitation or upgrade
of an affordable ADU. Homeowners are also offered tax
relief to offset the negative effects of deed restrictions that
preserve the affordability of the units.
24
Through its Amnesty Program, the town of Barnstable
has successfully brought many of its illegal accessory units
into compliance, with the added benefit of increasing the
supply of affordable housing. Since the start of the pro-
gram, Barnstable has approved 160 affordable ADUs. Beth
Dillen, Special Projects Coordinator for the town’s Growth
Management Department, noted that “the ADU program
has been very well received and there has been no neigh-
borhood opposition.” The program has been successful in
converting existing illegal accessory apartments into code-
compliant ADUs. According to Building Commissioner
Tom Perry, “The benefit to this program is twofold. It is
increasing the affordable housing supply and it also makes
units, that before were unsafe and illegal, safe and legal.”
Wellfleet, Massachusetts —
Home of Oysters...and ADUs
Wellfleet is located in Barnstable County, Massachusetts.
Located on Cape Cod, Wellfleet is a tourist town with a
22
U.S. Census 2000, www.census.gov.
23
See Appendix D.
24
Town of Barnstable, Accessory Affordable Apartment Program, http://www.town.barnstable.ma.us/GrowthManagement/
CommunityDevelopment/AssessoryHousing/AAAP-BROCHURE_rev041206.pdf.
5

year-round population of 3,500, which increases to 17,000
in the summer months. Sixty-one percent of the land area
in Wellfleet is part of the Cape Cod National Seashore and
about 70 percent of the entire land area is protected from
development.
25
Wellfleet also has a growing concentration
of elderly residents 65 years and older. A housing needs
assessment study conducted by the town in 2006 recom-
mended the adoption of an affordable ADU program to
meet elderly housing needs and to increase the supply of
affordable multifamily rental units.
26
Interior ADU – Town of Wellfleet
Photo credit: Town of Wellfleet
The affordable ADU bylaw for Wellfleet allows up to three
ADUs per lot in any district, but requires approval of a
special permit from the Zoning Board of Appeals. Second-
ary units may be within, attached to, or detached from a
Detached ADU – Town of Wellfleet
Photo credit: Town of Wellfleet
primary structure, and may not be larger than 1,200 square
feet. Homeowners with pre-existing attached and noncon-
forming accessory apartments may only make changes that
increase the conformity of the structures.
27
Unless the provisions are specifically waived, the con-
struction of new ADUs must conform to all zoning bylaw
provisions and the owner of the property must occupy
either the ADU or the primary dwelling. Detached units
must comply with all setback requirements. Owners are
required to rent to low- or moderate-income households.
Maximum rents follow the Fair Market Rental Guidelines
published by HUD and the property owners must submit
annual information on rents to be charged.
To encourage participation in the ADU program, Wellfleet
has instituted a new affordable accessory dwelling unit loan
program.
28
The program offers interest-free loans for
homeowners to develop affordable accessory units. The
funds can also be used by homeowners to bring their ADU
up to code. Wellfleet offers tax exemptions to home-
owners on the portion of the property that is rented as an
affordable unit. According to Nancy Vail, Assessor for the
Town of Wellfleet, the combined tax savings for all ADU
property owners totaled $7,971.17 for fiscal year 2008.
Sixteen units have been approved since the start of the
program in November 2006.
Fauquier County, Virginia
Fauquier County is a largely rural county located about
50 miles outside of Washington, D. C. Beginning in 1967,
Fauquier County adopted strict zoning regulations to
limit growth to nine defined areas as a means of preserv-
ing farmland and open space; in effect, establishing growth
boundaries.
29
However, the county population is rapidly
increasing. The 2006 U.S. Census population estimate for
Fauquier County was 66,170, a 20 percent increase from
2000. A needs assessment study by the Fauquier County
Affordable Housing Task Force found that between 2000
and 2006, the median housing price in Fauquier County
increased 127 percent, while the median household income
increased 21 percent. To accommodate its growing popula-
tion, especially the need for workforce housing, the county
encourages infill development within the nine defined
areas, and is active in reducing barriers to affordable
housing.
25
Town of Wellfleet, http://www.wellfleetma.org

26
Town of Wellfleet, Housing Needs Assessment, 2006, http://www.wellfleetma.org/Public_Documents/WellfleetMA_LocalCompPlan/

Appendix8.pdf.

27
See Appendix E.

28
Town of Wellfleet, Affordable Accessory Dwelling Unit Program, http://www.wellfleetma.org/Public_Documents/WellfleetMA_WebDocs/

AADU.pdf.

29
Keith Schneider, New Approaches to Shaping Community Futures, March 1997, Michigan Land Use Institute, http://www.mlui.org/

growthmanagement/fullarticle.asp?fileid=3862.

6

Fauquier County recognizes three different types of
accessory units: family dwellings, efficiency apartments, and
tenant houses.
30
Family dwelling units are detached acces-
sory units constructed for use by the homeowner’s family
member(s); they must be occupied by no more than five
people, at least one of them related to the owner. Family
dwelling units may be as large as1,400 square feet in size
and are permitted in both rural and many residentially
zoned areas. Efficiency apartments are alternatives to fam-
ily dwelling units and are attached to either the primary
residence or to an accessory structure, such as a garage.
The size is limited to 600 square feet or 25 percent of the
gross floor area of the main dwelling, whichever is greater.
Efficiencies may not be occupied by more than two unre-
lated people and are allowed in rural and residential-zoned
areas. Tenant houses are detached dwellings built on the
property for the purpose of supporting agricultural land
uses. At least one person occupying the tenant house must
work on the property. Tenant houses have no size limits.
They are allowed only on rurally zoned areas or properties
of at least 50 acres, with one tenant house for every 50
acres of a property.
Development of ADUs in Fauquier County depends on
the zoning, the size of the property, and availability of
septic/sewer and water services. Each of the unit types is
approved by the Fauquier Office of Zoning Permitting and
Inspections, with a building permit, provided that the units
meet zoning requirements. According to the county’s zon-
ing office, 155 accessory dwelling units and 37 efficiency
apartments were permitted from 1997 to 2007.
Conclusion
At the height of the suburbanization of the United States
in the 1950s and 1960s, high-density development became
undesirable. Instead, communities favored low-density
development defined by large-lot single-family homes.
Accessory apartments that were once a common feature
in many homes were excluded from zoning ordinances.
However, growing demand for affordable housing (coupled
with the limited amount of land available for development
in many communities) has led to changing attitudes about
the use and development of accessory apartments. An
increasing number of communities across the nation are
adopting flexible zoning codes within low-density areas in
order to increase their affordable housing supply.
Communities find that allowing accessory dwelling units is
advantageous in many ways. In addition to providing practi-
cal housing options for the elderly, disabled, empty nesters,
and young workers, ADUs can provide additional rental
income for homeowners. ADUs are smaller in size, do not
require the extra expense of purchasing land, can be devel-
oped by converting existing structures, and do not require
additional infrastructure. They are an inexpensive way for
municipalities to increase their housing supply, while also
increasing their property tax base. By providing affordable
housing options for low- and moderate-income residents,
communities can retain population groups that might
otherwise be priced out of the housing market.
The examples provided in the previous section involve
communities that have to rely on existing housing stock
to meet rising demand, either due to lack of developable
land or strict growth management regulations. Portland
and Fauquier County have adopted ADU ordinances to
increase housing supply within their growth boundaries.
Communities that are built out or have limited available
land benefit from allowing the development of accessory
units, as in Lexington and Wellfleet. Barnstable’s amnesty
program shows how to successfully bring a large number
of existing illegal accessory units into compliance. In addi-
tion to allowing ADUs in all residential zones, Santa Cruz
has attracted interest in ADU development by publishing
an ADU Manual and Plan Sets Book with seven prototype
designs for accessory units.
A community can tailor ADU ordinances to suit its
demographic, geographic, and socioeconomic characteris-
tics. The communities discussed in this case study
provide loan programs, tax incentives, streamlined permit-
ting, and reduced development fees as part of their ADU
programs. In order for an ADU program to succeed, it has
to be flexible, uncomplicated, include fiscal incentives, and
be supported by a public education campaign that
increases awareness and generates community support.
30
See Appendix F.
7

Appendix A — Town of Lexington, Massachusetts, Article V, 135-19, Accessory
Apartments
§ 135-19. Accessory apartments. [Amended 5-2-1988 ATM by Art. 41; 4-10-1989 ATM by Art. 41; 4-4-1990
ATM by Art. 36; 4-4-2005 ATM by Art. 10]
An accessory apartment is a second dwelling subordinate in size to the principal dwelling unit on an owner-occupied lot,
located in either the principal dwelling or an existing accessory structure. The apartment is constructed so as to maintain
the appearance and essential character of a one-family dwelling and any existing accessory structures. Three categories
of accessory apartments are permitted: by-right accessory apartments, which are permitted as of right, and special permit
accessory apartments and accessory structure apartments, which may be allowed by a special permit.
A. General objectives. The provision of accessory dwelling units in owner-occupied dwellings is intended to:
(1) Increase the number of small dwelling units available for rent in the Town;
(2) Increase the range of choice of housing accommodations;
(3) Encourage greater diversity of population with particular attention to young adults and senior citizens;

and

(4) Encourage a more economic and energy-efficient use of the Town’s housing supply while maintaining
the appearance and character of the Town’s single-family neighborhoods.
B. Conditions and requirements applicable to all accessory apartments.
(1) General.
(a) There shall be no more than two dwelling units in a structure, and no more than two dwelling
units on a lot.
(b) There shall be no boarders or lodgers within either dwelling unit.
(c) No structure that is not connected to the public water and sanitary sewer systems shall have
an accessory apartment.
(d) The owner of the property on which the accessory apartment is to be created shall occupy one or the
other of the dwelling units, except for temporary absences as provided in Subsection B (l) (e). For the
purposes of this section, the “owner” shall be one or more individuals who constitute a family, who
hold title directly or indirectly to the dwelling, and for whom the dwelling is the primary residence…
(2) Exterior appearance of a dwelling with an accessory apartment. The accessory apartment shall be designed so
that the appearance of the structure maintains that of a one-family dwelling….
(3) Off-street parking. There shall be provided at least two off-street parking spaces for the principal dwelling unit
and at least one off-street parking space for the accessory apartment….
C. By-right accessory apartments shall be permitted so long as the requirements set forth in
the §135-19B are satisfied and the following criteria in this section are met:
A - 1

(1) The lot area shall be at least 10,000 square feet.
(2) The apartment shall be located in the principal structure.
(3) The maximum gross floor area of the by-right accessory apartment shall not exceed 1,000 square feet.
(4) There shall not be more than two bedrooms in a by-right accessory apartment.
(5) There shall be no enlargements or extensions of the dwelling in connection with any by-right accessory

apartment except for minimal additions necessary to comply with building, safety or health codes, or for

enclosure of an entryway, or for enclosure of a stairway to a second or third story.

(6) The entire structure containing the by-right accessory apartment must have been in legal existence for a
minimum of five years at the time of application for a by-right accessory apartment.
D. Special permit accessory apartments. If a property owner cannot satisfy the criteria for by-right accessory
apartments that are set forth in § 135-19C above, the property owner may apply for a special permit from the
Board of Appeals….
E. Accessory structure apartments. Notwithstanding any provisions of this Zoning By-Law that state an accessory
apartment shall be located in a structure constructed as a detached one-family dwelling and the prohibition in §
135-35D against having more than one dwelling on a lot, the Board of Appeals may grant a special permit as provided
in § 135-16, Table 1, line 1.22C, to allow the construction of an accessory apartment in an existing accessory
structure which is on the same lot in the RS, RT, KO, RM or CN District as an existing one-family dwelling provided:
(1) Lot area is at least 18,000 square feet if in the RS, RT, or CN District, at least 33,000 square feet if in the RO
District, and at least 125,000 square feet if in the RM District;
(2) The structure containing the accessory structure apartment was in legal existence for a minimum of five years
and had a minimum of 500 square feet of gross floor area as of five years prior to the time of application;
(3) The maximum gross floor area of the accessory structure apartment does not exceed 1,000 square feet. An
addition to an accessory structure may be permitted, but no addition shall be allowed which increases the gross
floor area of the structure to more than 1,000 square feet. The gross floor area for the accessory apartment
shall not include floor area used for any other permitted accessory use. The accessory apartment cannot
contain floor area that has been designed, intended or used for required off-street parking to serve the principal
dwelling;…
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Appendix B — City of Santa Cruz, California, Title 24, Zoning Ordinance, Chapter
24.16, Part 2: ADU Zoning Regulations
24.16.100 Purpose.
The ordinance codified in this part provides for accessory dwelling units in certain areas and on lots developed or
proposed to be developed with single-family dwellings. Such accessory dwellings are allowed because they can contribute
needed housing to the community’s housing stock. Thus, it is found that accessory units are a residential use which is
consistent with the General Plan objectives and zoning regulations and which enhances housing opportunities that are
compatible with single-family development…
24.16.120 Locations Permitted.
Accessory dwelling units are permitted in the following zones on lots of 5000 square feet or more…
24.16.130 Permit Procedures.
The following accessory dwelling units shall be principally permitted uses within the zoning districts specified in Section
24.16.120 and subject to the development standards in Section 24.16.160.
1. Any accessory dwelling unit meeting the same development standards as permitted for the main building in the
zoning district, whether attached or detached from the main dwelling.
2. Any single story accessory dwelling unit.
Any accessory dwelling unit not meeting the requirements above shall be conditionally permitted uses within
the zoning districts specified in Section 24.16.120 and shall be permitted by administrative use permit at a

public hearing before the zoning administrator, subject to the findings per Section 24.16.150 and the

development standards in Section 24.16.160…
24.16.160 Design and Development Standards.
All accessory dwelling units must conform to the following standards:
1. Parking. One parking space shall be provided on-site for each studio and one bedroom accessory unit. Two
parking spaces shall be provided on site for each two bedroom accessory unit. Parking for the accessory unit is in
addition to the required parking for the primary residence. (See Section 24.16.180 for parking incentives.)
2. Unit Size. The floor area for accessory units shall not exceed five hundred square feet for lots between 5000 and
7500 square feet. If a lot exceeds 7500 square feet, an accessory unit may be up to 640 square feet and, for lots
in excess of 10,000 square feet, a unit may be up to 800 square feet. In no case may any combination of buildings
occupy more than thirty percent of the required rear yard for the district in which it is located, except for units
which face an alley, as noted below. Accessory units that utilize alternative green construction methods that cause
the exterior wall thickness to be greater than normal shall have the unit square footage size measured similar to
the interior square footage of a traditional frame house.
3. Existing Development on Lot. A single-family dwelling exists on the lot or will be constructed in conjunction with
the accessory unit.
4. Number of Accessory Units Per Parcel. Only one accessory dwelling unit shall be allowed for each parcel…
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24.16.170 Deed Restrictions.
Before obtaining a building permit for an accessory dwelling unit the property owner shall file with the county recorder
a declaration of restrictions containing a reference to the deed under which the property was acquired by the present
owner and stating that:
1. The accessory unit shall not be sold separately.
2. The unit is restricted to the approved size.
3. The use permit for the accessory unit shall be in effect only so long as either the main residence, or the accessory
unit, is occupied by the owner of record as the principal residence…
26.16.180 Zoning Incentives.
The following incentives are to encourage construction of accessory dwelling units.
1. Affordability Requirements for Fee Waivers. Accessory units proposed to be rented at affordable rents as
established by the city, may have development fees waived per Part 4 of Chapter 24.16 of the Zoning Ordinance...
2. Covered Parking. The covered parking requirement for the primary residence shall not apply if an accessory
dwelling unit is provided…
24.16.300 Units Eligible for Fee Waivers.
Developments involving residential units affordable to low or very-low income households may apply for a waiver of the
following development fees:
1. Sewer and water connection fees for units affordable to low and very low income households.
2. Planning application and planning plan check fees for projects that are one hundred percent affordable to low
and very-low income households.
3. Building permit and plan check fees for units affordable to very-low income households.
4. Park land and open space dedication in-lieu fee for units affordable to very low income households.
5. Parking deficiency fee for units affordable to very-low income households.
6. Fire fees for those units affordable to very-low income households.
(Ord. 93-51 § 6, 1993).
24.16.310 Procedure for Waiver of Fees.
A fee waiver supplemental application shall be submitted at the time an application for a project with affordable units is

submitted to the city.

(Ord. 93-51 § 6, 1993)

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Appendix C — City of Portland, Oregon, Title 33, Chapter 33.205: Accessory
Dwelling Units
333.205.010 Purpose
Accessory dwelling units are allowed in certain situations to:
&bull; Create new housing units while respecting the look and scale of single-dwelling development;
• Increase the housing stock of existing neighborhoods in a manner that is less intense than alternatives;
• Allow more efficient use of existing housing stock and infrastructure;
• Provide a mix of housing that responds to changing family needs and smaller households;
• Provide a means for residents, particularly seniors, single parents, and families with grown children, to
remain in their homes and neighborhoods, and obtain extra income, security, companionship and services;
and
• Provide a broader range of accessible and more affordable housing.
33.205.020 Where These Regulations Apply
An accessory dwelling unit may be added to a house, attached house, or manufactured home in an R zone, except
for attached houses in the R20 through R5 zones that were built using the regulations of 33.110.240.E, Duplexes and
Attached Houses on Corners.
33.205.030 Design Standards...
C. Requirements for all accessory dwelling units. All accessory dwelling units must meet the following:
1. Creation. An accessory dwelling unit may only be created through the following methods:
a. Converting existing living area, attic, basement or garage;
b. Adding floor area;
c. Constructing a detached accessory dwelling unit on a site with an existing house, attached
house, or manufactured home; or
d. Constructing a new house, attached house, or manufactured home with an internal or
detached accessory dwelling unit.
2. Number of residents. The total number of individuals that reside in both units may not exceed the
number that is allowed for a household…
5. Parking. No additional parking is required for the accessory dwelling unit. Existing required parking for
the house, attached house, or manufactured home must be maintained or replaced on-site.
6. Maximum size. The size of the accessory dwelling unit may be no more than 33% of the living area of
the house, attached house, or manufactured home or 800 square feet, whichever is less…
D. Additional requirements for detached accessory dwelling units. Detached accessory dwelling units must
meet the following.
1. Setbacks. The accessory dwelling unit must be at least:
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a. 60 feet from the front lot line; or
b. 6 feet behind the house, attached house, or manufactured home.
2. Height. The maximum height allowed for a detached accessory dwelling unit is 18 feet.
3. Bulk limitation. The building coverage for the detached accessory dwelling unit may not be larger than
the building coverage of the house, attached house, or manufactured home. The combined building
coverage of all detached accessory structures may not exceed 15 percent of the total area of the site…
33.205.040 Density
In the single-dwelling zones, accessory dwelling units are not included in the minimum or maximum density calculations
for a site. In all other zones, accessory dwelling units are included in the minimum density calculations, but are not
included in the maximum density calculations.
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Appendix D — Town of Barnstable, Massachusetts, Chapter 9, Article II -
Accessory Apartments and Apartment Units
§ 9-12. Intent and purpose.
A. The intent of this article is to provide an opportunity to bring into compliance many of the currently unpermitted
accessory apartments and apartment units in the Town of Barnstable, as well as to allow the construction of new
dwelling units accessory to existing single-family homes to create additional affordable housing.
B. This article recognizes that although unpermitted and unlawfully occupied, these dwelling units are filling a
market demand for housing at rental costs typically below that of units which are and have been lawfully

constructed and occupied.

C. It is in the public interest and in concert with its obligations under state law, for the Town of Barnstable to offer a
means by which so-called unpermitted and illegal dwelling units can achieve lawful status, but only in the manner
described below.
D. It is the position of the Town of Barnstable that the most appropriate mechanism for allowing for the conversion
of unlawful dwelling units to lawful units is found in MGL c. 40B, §§ 20 to 23, the so-called “Comprehensive Permit”
program. This provision of state law encourages the development of low- and moderate-income rental and
owner-occupied housing and provides a means for the Board of Appeals to remove local barriers to the creation of
affordable housing units. These barriers include any local regulation such as zoning and general ordinances that
may be an impediment to affordable housing development.
E. The Local Comprehensive Plan states that the Town should commit appropriate resources to support affordable
housing initiatives. Under this article, the Town commits the following resources to support this affordable
housing initiative:
(1) Waiver of fees for the inspection and monitoring of the properties identified under this article;
(2) Designation of Town staff to assist the property owner in navigating through the process established under
this article;
(3) To the extent allowable by law, the negative effect entailed by the deed restriction involved will be reflected in
the property tax assessment; and
(4) To assist property owners in locating available municipal, state and federal funds for rehabilitating and
upgrading the properties identified under this article.
F. The Local Comprehensive Plan supports, in conjunction with a variety of other strategies, the conversion of
existing structures for use as affordable housing…
§ 9-14.Amnesty program.
Recognizing that the success of this article depends, in part, on the admission by real property owners that their
property may be in violation of the Zoning Ordinances of the Town, Editor’s Note: See Ch. 240, Zoning. the Town hereby
establishes the following amnesty program:
A. The threshold criteria for units being considered as units potentially eligible for the amnesty program are:
(1) Real property containing a dwelling unit or dwelling units for which there does not exist a validly issued
variance, special permit or building permit, does not qualify as a lawful, nonconforming use or structure, for
any or all the units, and that was in existence on a lot of record within the Town as of January 1, 2000; or
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(2) Real property containing a dwelling unit or dwelling units which were in existence as of January 1, 2000, and
which have been cited by the Building Department as being in violation of the Zoning Ordinance; and…
B. The procedure for qualifying units that meet the threshold criteria for the amnesty program is as follows:
(1) The unit or units must either be a single unit accessory to an owner occupied single-family dwelling or one
or more units in a multifamily dwelling where there exists a legal multifamily use but one or more units
are currently unpermitted;
(2) The unit(s) must receive a site approval letter under the Town’s local Chapter 40B program;
(3) The property owner must agree that if s/he receives a comprehensive permit, the unit or units for which
amnesty is sought will be rented to a person or family whose income is 80% or less of the area median income
(AMI) of Barnstable-Yarmouth Metropolitan Statistical Area (MSA) and shall further agree that rent (including
utilities) shall not exceed the rents established by the Department of Housing and Urban Development (HUD)
for a household whose income is 80% or less of the median income of Barnstable-Yarmouth Metropolitan
Statistical Area. In the event that utilities are separately metered, the utility allowance established by
the Barnstable Housing Authority shall be deducted from HUD’s rent level.
(4) The property owner must agree, that if s/he receives a comprehensive permit, that s/he will execute a deed
restriction for the unit or units for which amnesty is sought, prepared by the Town of Barnstable, which runs
with the property so as to be binding on and enforceable against any person claiming an interest in the
property and which restricts the use of one or more units as rental units to a person or family whose income
is 80% or less of the median income of Barnstable-Yarmouth Metropolitan Statistical Area (MSA)…
§ 9-15. New units accessory to single-family owner-occupied dwellings.
For a proposed new unit to be eligible for consideration under the local chapter 40B program, it must be a single
unit, accessory to an owner-occupied single-family dwelling, to be located within or attached to an existing residential
structure or within an existing building located on the same lot as said residential structure and comply with the
following:
A. The unit(s) must receive a site approval letter under the Town’s local Chapter 40B program;
B. The property owner must agree that if s/he receives a comprehensive permit, the accessory dwelling unit will be
rented to a person or family whose income is 80% or less of the area median income (AMI) of Barnstable-
Yarmouth Metropolitan Statistical Area (MSA) and shall further agrees that rent (including utilities) shall not
exceed the rents established by the Department of Housing and Urban Development (HUD) for a household
whose income is 80% or less of the median income of Barnstable-Yarmouth Metropolitan Statistical Area.
In the event that utilities are separately metered, the utility allowance established by the Barnstable
Housing Authority shall be deducted from HUD’s rent level.
C. The property owner must agree, that if s/he receives a comprehensive permit, that s/he will execute a deed
restriction for the unit, prepared by the Town of Barnstable, which runs with the property so as to be binding on
and enforceable against any person claiming an interest in the property and which restricts the use of the one
unit as a rental unit to a person or family whose income is 80% or less of the median income of Barnstable-
Yarmouth Metropolitan Statistical Area (MSA)...
D - 2

Appendix E — Town of Wellfleet, Massachusetts, 6.21 Affordable Accessory
Dwelling Units
Purpose: For the purpose of promoting the development of affordable rental housing in Wellfleet for year-round
residents, a maximum of three affordable accessory dwelling units per lot may be allowed subject to the requirements,
standards and conditions listed below:
6.21.1 Up to three affordable accessory dwelling units per lot may be allowed in any district by Special Permit from the
Zoning Board of Appeals.
6.21.2 Affordable accessory dwelling units created under this by-law shall be occupied exclusively by income-eligible
households, as defined by the guidelines in numbers 6.21.4 and 6.21.5 below. The affordability requirements of this by-law
shall be imposed through conditions attached to the Special Permit issued by the Zoning Board of Appeals. No accessory
apartment shall be constructed or occupied until proof of recording is provided to the Inspector of Buildings.
6.21.3 Requirements and Standards
A. Affordable accessory dwelling units may be located within or attached to a principal dwelling,
principal structure, a garage or constructed as a detached unit.
B. Affordable accessory dwelling units shall not be larger than one thousand two hundred (1,200) square
feet of Livable Floor Area as that term is defined in Section II of this Zoning By-law.
C. Affordable accessory dwelling units within or attached to a principal dwelling, principal structure or
garage that is pre-existing nonconforming shall not increase the nonconforming nature of that
structure, except that any pre-existing accessory building may be eligible for conversion to an
affordable accessory dwelling unit.
D. Newly constructed detached accessory units shall comply with all applicable provisions of the Zoning
By-law unless they are specifically waived by this by-law. Newly constructed detached accessory units
shall comply with all setback requirements listed in Sections 5.4.2 of this Zoning By-law.
E. Owners of residential property may occupy as a primary residence either the principal or accessory
dwelling. For the purposes of this section, the “owner” shall mean one who holds legal or beneficial
title.
F. Septic systems are required to meet current Title 5 standards and shall be reviewed and approved by
the Health Agent.
G. The Inspector of Buildings and Health Agent shall inspect the premises for compliance with public
safety and public health codes.
H. No affordable accessory dwelling unit shall be separated by ownership from the principal dwelling
unit or principal structure. Any lot containing an affordable accessory dwelling unit shall be subject to
a recorded restriction that shall restrict the lot owner’s ability to convey interest in the affordable
accessory dwelling unit, except leasehold estates, for the term of the restriction.
6.21.4 All occupants of the affordable accessory dwelling unit shall upon initial application and annually thereafter on
the first of September, submit to the Town or its agent necessary documentation to confirm their eligibility for the
dwelling unit. Specifically, all dwelling units must be rented to those meeting the guidelines for a low or moderate-income
E - 1

family. For the purpose of this section, low income families shall have an income less than eighty (80) percent of the
Town of Wellfleet median family income, and moderate income families shall have an income between eighty (80) and
one hundred twenty (120) percent of the Town of Wellfleet median family income, as determined by the United States
Department of Housing and Urban Development (HUD) Published Income Guidelines, and as may from time to time be
amended.
6.21.5 Maximum rents shall be established in accordance with HUD published Fair Market Rental Guidelines. Property
owners are required to submit to the Town or its agent information on the rents to be charged. Each year thereafter
on the first of September, they shall submit information on annual rents charged to the Town or its agent. Forms for this
purpose shall be provided. Rents may be adjusted annually in accordance with amendments to the Fair Market Rental
Guidelines.
6.21.6 Procedure
A. The property owner shall complete and submit an application for a Special Permit to the Zoning Board
of Appeals in accordance with the Wellfleet Zoning Board of Appeals Rules and Procedures.
B. The Zoning Board of Appeals shall hold a public hearing in accordance with the procedures and
requirements set forth in Section 9 of Massachusetts General Law, Chapter 40A and the Wellfleet
Zoning By-law, Section 8.4.2 .
C. Appeal under this section shall be taken in accordance with Section 17 of Massachusetts General Law,
Chapter 40A.
D. The property owner shall complete and submit to the Inspector of Buildings an application for a
Building Permit to allow a change in use.
E. The property owner shall obtain a Certificate of Occupancy from the Inspector of Buildings prior to the
affordable accessory dwelling unit being occupied.
Penalty – Failure to comply with any provision of this section may result in fines established in Section 8.3 of the
Wellfleet Zoning By-laws.
E - 2

Appendix F — Fauquier County, Virginia Zoning Ordinance
ARTICLE 5 — ADMINISTRATIVE PERMITS, SPECIAL PERMITS AND SPECIAL EXCEPTIONS
5-104 Standards for an administrative permit for an Efficiency Apartment
1. Such a unit shall not be occupied by more than two persons.
2. Not more than one such unit shall be located on a lot.
3. Such a unit shall contain no more than 600 square feet of gross floor area or 25% of the total gross floor of
the dwelling, whichever is greater.
4. Such a unit shall be located only on the same lot as the residence of the owner of the lot.
5. Architectural features of such a unit shall conform with the single family character of the neighborhood
(e.g., no additional front doors).
5-105 Standards for an administrative permit for a Family Dwelling Unit
1. Such a unit shall not be occupied by more than five (5) persons, at least one of whom must be the natural
or adopted parent, grandparent, child, grandchild, brother or sister of the owner and occupant of the
single family residence on the same lot. Or, the lot owner may live in the family dwelling unit and allow
such family members to reside in the main house. In either case, the lot owner must reside on the
property.
2. Such a unit may be 1,400 square feet of gross floor area.
3. No dwelling units other than the principal structure (a single family dwelling) and one such family
dwelling unit shall be located on one lot...
ARTICLE 6 - ACCESSORY USES, ACCESSORY SERVICE USES AND HOME OCCUPATIONS
6-102 Permitted Accessory Uses
Accessory uses and structures shall include, but are not limited to, the following uses and structures, provided that such
uses or structure shall be in accordance with the definition of Accessory Use contained in Article 15…
9. Guest house or rooms for guests in an accessory structure, but only on lots of at least two (2) acres and
provided such house is without kitchen facilities, is used for the occasional housing of guests of the
occupants of the principal structure and not as rental units or for permanent occupancy as housekeeping
units...
14. Quarters of a caretaker, watchman or tenant farmer, and his family, but only in the Rural Districts at a
density not to exceed one (1) unit per fifty (50) acres...
31. The letting for hire of not more than two rooms to not more than two persons for periods no shorter than
one month...
F - 1

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