PIONEER INSTITUTE
Pioneer’s Mission
Pioneer Institute is an independent, non-partisan, privately funded research organization that
seeks to improve the quality of life in Massachusetts through civic discourse and intellectually
rigorous, data-driven public policy solutions based on free market principles, individual liberty and
responsibility, and the ideal of effective, limited and accountable government.
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committed to the principles Pioneer espouses. To ensure its independence, Pioneer does not accept government grants.
is paper is a publication of Pioneer Oppor-
tunity, which seeks to keep Massachusetts
competitive by promoting a healthy business
climate, transparent regulation, small business
creation in urban areas and sound environmen-
tal and development policy. Current initiatives
promote market reforms to increase the supply
of aordable housing, reduce the cost of doing
business, and revitalize urban areas.
Pioneer Health seeks to refocus the Massa-
chusetts conversation about health care costs
away from government-imposed interventions,
toward market-based reforms. Current initia-
tives include driving public discourse on Med-
icaid; presenting a strong consumer perspective
as the state considers a dramatic overhaul of the
health care payment process; and supporting
thoughtful tort reforms.
Pioneer Public seeks limited, accountable gov-
ernment by promoting competitive delivery
of public services, elimination of unnecessary
regulation, and a focus on core government
functions. Current initiatives promote reform
of how the state builds, manages, repairs and
nances its transportation assets as well as pub-
lic employee benet reform.
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tion options available to parents and students,
drive system-wide reform, and ensure account-
ability in public education. e Center’s work
builds on Pioneer’s legacy as a recognized leader
in the charter public school movement, and as
a champion of greater academic rigor in Mas-
sachusetts’ elementary and secondary schools.
Current initiatives promote choice and competi-
tion, school-based management, and enhanced
academic performance in public schools.
3
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Table of Contents
Executive Summary
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4
Background on the Study
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5
Housing in Greater Boston
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5
Concerns about Character of Neighborhoods
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6
Baseline Findings from the 2004–2006 Study
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7
Master Plans And Housing Production Plans
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7
Recent Changes To Local Bylaws and Ordinances
_______
7
The Regulation of Accessory
Dwelling Units Without Residency Restrictions
_________
7
In-Law Apartments
___________________________
11
Short Term Rentals (Like Airbnb)
_________________
11
Municipalities With No Zoning For Adus
____________
11
Permitting Numbers
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11
Recommendations
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12
Appendix
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13
4
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
In Belmont, ADUs are only allowed in detached historic
structures such as antique carriage houses. Most houses lack
historic accessory buildings.
In addition to the 37 municipalities that allow ADUs,
another 31 municipalities only allow them to be occupied
by relatives of the homeowners or caretakers; the units are
supposed to be removed when the relative moves out. Some
apartments get removed, which is a terrible waste of housing
capacity during a housing crisis. Other apartments are rented
out illegally, without the safety inspections permitted apart-
ments get.
Municipal planners and housing advocates have been
working for decades to pass ADU bylaws and ordinances. In
the last decade, almost half of the 100 Boston-area municipal-
ities have adopted either a master plan or housing production
plan that recommends allowing ADUs more liberally. At least
one in ve municipalities did revise zoning for ADUs in that
same time period. Belmont, Swampscott, and Hudson voted
to allow ADUs (unrestricted to relatives.) Ipswich, Middleton,
and Milford revised their provisions to switch from allowing
temporary family-apartments to allowing regular ADUs.
Lexington, Newton, Carlisle, and a few other municipalities
voted to allow ADUs in detached structures, and liberalized
other aspects of their regulations. Hamilton used to allow
ADUs only on lots 10 acres or bigger; now the town allows
ADUs on any-sized lot.
Meanwhile, despite the signicant eorts to revise the zon-
ing, the majority of municipalities still do not allow ADUs as
rentals, and most municipalities that permit them still over-re-
strict them. Progress across the region has been remarkably
slow, in a time of rapidly increasing demand for housing.
Homeowner-voters can be reassured that new rental hous-
ing that could be added as ADUs would be highly dispersed
and barely visible. e houses are owner-occupied; the land-
lord lives next to the ADU renters, so the risk of property-ne-
glect or loud parties is minimal. e houses also have to look
like single family houses. Since household sizes are shrinking,
new residents in ADUs might maintain current neighborhood
population densities, but are unlikely to increase them.
Moreover, ADUs are permitted at such low levels now —
only 2.5 permits annually per municipality where they are
allowed — that permitting levels could increase substantially
without being at all noticeable in neighborhoods. If the region
were to average ve permits per municipality per year across
100 municipalities, over a decade, ADUs could provide 5,000
apartments, dispersed among 538,000 single family houses.
Less than one in 100 houses would have an ADU, yet the new
rentals would house thousands of people.
Every municipality should allow ADUs to be added to
owner-occupied single family houses and to be rented out. e
ADUs should not be restricted to large old houses on big lots,
Even in the midst of a housing crisis, zoning laws prohibit
most homeowners in cities and towns around Boston from
adding accessory dwelling units (ADUs) to their single family
houses. An ADU is an apartment within or behind an own-
er-occupied single family house that appears from the street to
be a single-family as opposed to a two-family house.
Only 37 out of 100 cities and towns surrounding Boston
allow for ADUs to be put in and rented out — and typically
with signicant restrictions on the houses that could qualify
for gaining an ADU. Another 31 municipalities allow tem-
porary ADUs for occupancy by relatives of the homeowner or
caretakers. e remaining 32 municipalities have no zoning
for ADUs.
Given the restrictive zoning, few ADUs are being creat-
ed legally. is paper provides a detailed survey of the ADU
regulations in the region, and argues that these regulations are
overly restrictive, particularly in light of the housing crisis and
recent demographic trends in Greater Boston.
Executive Summary
Of the 100 cities and towns in the Metropolitan Area Plan-
ning Council (MAPC) region outside the City of Boston,
only 37 allow a homeowner to create an accessory apartment
and rent it to persons other than family members or caregiv-
ers. However, only a fraction of the single-family homes in
those municipalities are eligible for an ADU because of other
restrictions.
For example, Manchester allows ADUs, but only on lots
twice the minimum lot size for the district, and only in hous-
es built before 1984. Most houses in the municipality do not
qualify, and the town rarely gets any applications.
In Dedham, ADUs can be added to houses where the lot
is 10 percent bigger than the minimum lot size, but most of
the houses in Dedham are on non-conforming lots, smaller
than the zoning requires. Dedham has more than 6,000 single
family houses, but the town receives only a few applications
per year to add ADUs.
As is the case in Manchester and Dedham, 16 of the 37
municipalities that allow ADUs limit them to houses on lots
bigger than a certain size. In Duxbury and Wenham, the lot
needs to be 20,000 square feet, or almost a half-acre.
In Medeld, ADUs are allowed in houses built before
1938 that have a minimum oor area of 2,000 square feet. In
Burlington, they are allowed in houses that had at least 1,800
square feet of oor area, as of 1989. Before the 1990s, most
new houses were not that big; the median size of new single
family houses in the Northeast did not surpass 1,800 square
feet until 1987, and did not top 2,000 square feet until 1992.
In Weston, ADUs are only allowed in houses that have at least
3,000 square feet.
5
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
the collection of the ADU bylaws and ordinances in the 100
municipalities and compared them on a number of metrics,
explained below. e study also asked local planners and
building inspectors the following questions:
How many accessory dwelling units have been permitted in
each of the last three years?
Approximately how many accessory units have been
permitted town-wide or city-wide, if that information is
available?
Have any permit applications for ADUs been rejected in the
last ve years? For what reasons?
What have been the challenges, if any, of enforcing
requirements for accessory dwelling units, after the units
have been permitted?
How much sta time is devoted in an average month to process
applications for permits for accessory dwelling units —
and to guide the process and enforce the rules?
Researchers have been collecting the data from September
2017 through July 2018. Once a municipality’s zoning is sur-
veyed for the research, it is not checked again for changes. So,
for example, if a municipality did not allow ADUs in Novem-
ber of 2017 when its zoning was reviewed, but amended the
zoning to allow ADUs at the annual Town Meeting in May of
2018, that change will not be reected in the study.
Housing in Greater Boston
Even if nobody new were moving to Greater Boston, the
region would need more housing due to demographic shifts.
e baby boomers are now largely empty nesters, and their
grown kids are forming new households, while delaying mar-
riage. When household sizes shrink and the population does
not, demand for residences increases. In addition, the region
is attracting new people, as happens when hundreds of thou-
sands of jobs get created.
Production of new housing has not been keeping up with
escalating demand at least in part because local voters are
highly cautious about allowing new housing in their cities and
towns. Renters and homebuyers are bidding up the prices of
the limited supply of residences, with the wealthiest winning
the contest. People of all income levels should be able to live
near centers of employment.
To stabilize prices and house the growing population, local
and state lawmakers level will need to decide where new hous-
ing can go. Greater Boston does not have a lot of developable
green space, such as farms, woods, or meadows, where neigh-
borhoods might rise, and popular support for protecting green
space is strong. New housing can generally be put in three kinds
of places: A) business districts, including historic downtowns
and newer strip malls, B) oce or industrial districts, often
on the edge of a municipality near a highway, or C) existing
or to antique accessory buildings. Most houses within walking
distance of stores and public transportation are on smaller lots;
it’s good for both the region’s trac levels — and its people —
to have more residents in walkable neighborhoods where cars
aren’t needed for every activity.
Cautious voters seeking to protect the character of their
single-family neighborhoods should be reassured that they risk
virtually nothing by allowing ADUs to provide much-needed
housing, and they could potentially gain rental income.
Background On The Study
In 2017, the Massachusetts Smart Growth Alliance commis-
sioned a study on local regulation of residential development
in eastern Massachusetts. e study is funded by a coalition
of organizations including the Smart Growth Alliance, Cit-
izens’ Housing and Planning Association, Home Builders
& Remodelers Association of Massachusetts, Massachusetts
Association of Realtors, Massachusetts Housing Partnership,
MassHousing, and the Metropolitan Area Planning Council
(MAPC). A committee that includes representatives of the
funding organizations, as well as municipal planners and rep-
resentatives of environmental organizations, provided input
into the research design.
e research is designed to update a 2004 – 2006 study
produced by Pioneer Institute and the Rappaport Institute.
In the 2004 – 2006 study, researchers answered more than
100 questions about residential zoning, road design standards,
local septic system requirements, and local wetlands regula-
tions for the 187 cities and towns within 50 miles of Boston,
but not including Boston itself (Zoning in the City of Bos-
ton is governed by a state statute dierent from the one that
governs zoning in all other Massachusetts municipalities).
e updated study asks many of the same questions and also
includes new ones. e updated study covers the 100 cities and
towns that are served by MAPC, but again not including Bos-
ton. e updated study covers zoning for ADUs, multi-family
housing, and cluster development (where houses are clustered
on a parcel and part of the land gets preserved as open space),
as well as road design standards and local septic system reg-
ulations.
e research includes a survey of zoning bylaws and ordi-
nances, along with the housing production plans and munici-
pal master plans that have been produced in the last decade in
the 100 cities and towns. is stage of the research is complete.
e research also includes survey questions sent to the
local director of planning, or to the building inspector when a
municipal planner is not available to answer questions. Plan-
ners and building inspectors from 53 of the 100 municipalities
have provided answers so far, although in some cases, not to
every question.
Regarding ADUs specically, the study has included
6
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Newton’s 2007 Comprehensive Plan: “ose living in
predominantly single-family areas generally wish them to
stay that way. ey wish those areas neither to be marginally
blurred into resembling the mixed single and two family
areas nor to be compromised by large-scale multifamily
developments being plopped into their midst.”
Wayland’s 2016 Housing Production Plan: “Within existing
residential neighborhoods, new multi-family housing is
generally not recommended because of concerns that it
would alter the single-family character of most of Wayland's
neighborhoods.”
Wellesley’s Draft Unied Plan 2018: “Goals for policies for
decision makers: Established single-family neighborhoods
maintain a predominantly single family character.”
Zoning to allow accessory apartments in single-family houses
explicitly addresses public concerns about changing the char-
acter of single-family neighborhoods. First, to add an ADU,
the homeowner must reside in the house. e owner occupancy
requirement means the landlord will be on site, living in close
proximity to the renters, perhaps making loud parties less likely,
and reducing the risk of the property being neglected.
Second, the house needs to maintain the appearance of
a single-family house. Bedford’s requirements regarding the
appearance of the house and ADU are typical:
“e accessory apartment shall be designed so that the
appearance of the structure remains that of a one fami-
ly dwelling, subject further to the following conditions and
requirements: (i) All stairways to second or third stories shall
be enclosed within the exterior walls of the dwelling. (ii) Any
new entrance shall be located on the side or in the rear of the
dwelling. (iii) Where there are two or more existing entrances
on the front facade of a dwelling, if modications are made
to any entrance, the result shall be that one appears to be the
principal entrance and the other entrances appear to be sec-
ondary.”
Newton’s regulations do allow for exterior staircases to be
added because construction of new internal staircases could
make projects too expensive or infeasible. Newton’s regula-
tions state:
“3. Exterior alterations are permitted provided they are in
keeping with the architectural integrity of the structure and
the residential character of the neighborhood, including, but
not limited to, the following considerations:
a. e exterior nish material should be the same or visually
consistent in type, size, and placement, as the exterior n-
ish material of the remainder of the building;
b. e roof pitch should be consistent with the predominant
roof pitch of the remainder of the building;
c. Trim should be consistent in type, size, and location as the
trim used on the remainder of the building;
d. Windows should be consistent with those of the remain-
der of the building in proportion and orientation;
residential neighborhoods. Much planning is now going into
the residential development of the rst two categories of plac-
es. Wellesley’s 2018 Draft Unied Plan states: “Participants
in the Unied Plan public meetings saw the commercial,
oce and industrial districts as the most acceptable locations
to construct new housing that is not single-family housing.”
ree-fourths of the region’s municipalities now have zoning
for apartments and condos above stores, with many of these
zoning provisions adopted in the last decade. Unfortunately,
the projected buildout of currently planned growth districts
is not nearly enough to satisfy projected demand for housing.
Concerns About Neighborhood Character
Homeowners are understandably cautious about allowing
increases in housing density in their neighborhoods. ey
might be worried about more trac, the paving over of grassy
yards and gardens for parking, the aesthetics of new construc-
tion, the hassle of living next to construction, and a loss of
privacy. ey might worry that new renter-neighbors will be
less invested in the neighborhood than homeowners. Further-
more, for most homeowners, their house is their single larg-
est investment, and unlike a portfolio of stocks, it cannot be
diversied against risk; voting against changes in the neigh-
borhood is a way of protecting their investment.
Many municipal master plans emphasize that residents
would like to protect the character of single family neighbor-
hoods and the small-town feel of the community:
Medway’s 2009 Master Plan: “We enjoy a ‘small town
feel’… We are what other towns used to be, and we have
challenges ahead in managing our growth so we can retain
the character that we all cherish.”
Dover’s 2013 Master Plan: “People choose to reside in Dover
because it oers a more rural alternative to the suburban
development patterns of most surrounding towns.”
Arlington’s 2015 Master Plan: “Residents seem concerned
that additional development will be out of scale or character
with the qualities they value in their community.”
Medeld’s 2016 Housing Production Plan: “e town’s large
preservation areas, historic downtown, and neighborhoods
of single-family homes create a small-town character,
despite being close to a major metropolitan area.”
Randolph’s 2017 Master Plan: “e Town of Randolph
and its residents have expressed a desire to protect and
maintain the residential character of their single-family
neighborhoods, and to enhance the quality of town services
and amenities.”
Sudbury’s 2001 Master Plan, mentions vision statement
adopted by town meeting in 1998: “We value the town’s
essentially residential, low-density nature. A signicant
aspect of Sudbury’s charm and character is derived from its
rural/suburban feeling. Becoming more like towns nearer
Boston would not be considered progress.”
7
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
that several municipalities followed up on recommendations
in the plans. Several planners mentioned that addressing the
topic is on their agenda for the next year or two.
Recent Changes to Local Bylaws
and Ordinances
e research identies the years that the ADU provisions were
either adopted or last revised. e data is still being collected
from 22 of the 100 municipalities, but more than one in ve
have revised zoning for ADUs in the last decade, including:
2007: Gloucester, Hudson
2009: Belmont, Foxborough, Sudbury, Swampscott
2010: Wilmington
2012: Ipswich
2014: Brookline, Medeld
2015: Boxborough, Rockland
2016: Lexington, Medway
2017: Newton, Reading, Cambridge, Lincoln, Littleton,
Westwood, Carlisle, Concord
Belmont, Swampscott, and Hudson voted to allow ADUs
(unrestricted to relatives). ey did not allow ADUs when the
2004 study was conducted. Ipswich, Littleton, and Milford
revised their provisions to switch from allowing “family apart-
ments” restricted to relatives of the homeowners to allowing
ADUs that can be rented out without restricting who the res-
idents can be.
Several planners mentioned that ADUs are on their agen-
da to address with the planning board in the next year or two.
A few planners mentioned that they have had to prioritize
issues to take to the planning board and town meeting, so, for
example, they might address new zoning for mixed-use devel-
opment in the downtown rst, and then address ADUs.
The Regulation Of Accessory Dwelling Units
Without Residency Restrictions
e research has involved collecting the 68 ADU bylaws and
ordinances adopted in the 100 municipalities. e following
analysis is about the requirements in the 37 cities and towns
that allow ADUs without restricting occupancy to relatives
of the homeowner, caretakers, or qualifying low-income res-
idents.
Overall Restrictiveness
In the 37 municipalities that allow ADUs, the regulations
typically limit the houses that would be eligible for an ADU.
For example, Manchester allows ADUs, but only on lots twice
the size of the minimum lot size for the district, and only in
houses built before 1984. Most houses in the municipality do
e. Exterior staircases should be designed to minimize visual
intrusion and be complementary to the existing building;
f. e Commissioner of Inspectional Services shall seek
advice and counsel from the Director of Planning and
Development and/or the Urban Design Commission
where there is a question in the application of the above
rules.”
Baseline Findings from The 2004 – 2006 Study
According to the 2004 – 2006 study, only 50 of the 187
municipalities (27 percent) allowed homeowners to add acces-
sory apartments and rent them out to any person, as opposed
to allowing them for occupancy by relatives of the homeowner.
While allowing ADUs, the regulations restricted their use in
various ways. Some municipalities required, for example, that
the house have existed for a certain number of years or have
a certain amount of oor area. Hamilton’s 2002 Master Plan
Phase 1 Report noted, “e regulations for this option sig-
nicantly restrict the universe of eligible properties because in
order to qualify for an accessory apartment, the property must
have 10 acres of land.”
Another 46 of the municipalities (25 percent) allowed
accessory apartments only when relatives of the owner reside
in the apartment (or the primary dwelling if the owner is in
the accessory dwelling). Eleven more municipalities (6 per-
cent) restricted residence to certain categories of people (usu-
ally in addition to relatives): (1) elderly, (2) caretakers, and (3)
low-income residents.
To prevent occupancy restriction violations, many of the
regulations included extensive provisions about verication of
occupancy, usually through regular re-certication or re-per-
mitting of the units. After the relatives either move out or pass
away, the kitchen must be removed and the apartment reinte-
grated. For example, Dover’s bylaw stated: “Within 6 months
of the lapse of a Special Permit hereunder, the owner or own-
ers of the building containing an apartment shall dismantle
the cooking facilities of the apartment and restore the build-
ing to a single-family dwelling.” Two municipalities required
that the homeowner put down a surety bond to ensure that the
apartment will be reintegrated upon vacancy by the relatives
or sale of the house.
Master Plans And Housing Production Plans
In the last decade, 47 municipalities in the study sample of 100
adopted either a housing production plan or municipal master
plan that included recommendations regarding ADUs.
Carlisle’s 2015 Housing Production Plan recommends
changing the requirements for ADUs, and in 2017 Carlisle
revised the bylaw to allow ADUs more liberally. It appears
8
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Some municipalities, such as Cambridge, require that
owner/s submit a notarized letter that owner/s will live at the
house as primary residence, to get a permit for the ADU.
In Westwood, the owners need to submit an adavit every
four years certifying owner occupancy. Owners in Sudbury
are also supposed to certify compliance every four years. Can-
ton, Waltham, Milford, and Dedham require re-permitting,
renewal, or re-certication every three years. In Marsheld,
the owner is supposed to recertify annually. Newton also
requires annual certication.
Other municipalities have no requirements for re-certi-
cation, but specify that the special permit terminates upon
sale or transfer of the property. New owners need to re-apply.
Some regulations specify that the requirement for re-applica-
tion upon sale shall not dispossess current tenants.
A planner in one small town, where ADUs are allowed by
right with no requirements for permit renewal, said:
It is dicult to know for sure if units are being owner
occupied. We don’t inspect or review unless it’s brought
to our attention. In the four years that I have worked
here, there was one incident where the residence was not
owner-occupied. e building inspector contacted the
owner to let them know that the accessory apartment
could not be rented if the residence was not owner occu-
pied.
In Lincoln, the Zoning Board of Appeals sends out renew-
al letter annually. Several planners and inspectors mentioned
that it has been a challenge to establish a management system
to reliably make re-permitting and recertication happen. In
Dedham, homeowners are supposed to renew their ADU per-
mits every three years, but “virtually nobody comes to renew,”
said the building inspector. e issue can come up during the
sale, but the process to permit the unit might then take longer
than the sellers have. e process can take six weeks to ve
months in Dedham.
Restrictions on houses that qualify
ere are three common types of restrictions on the single
family houses that could qualify for an ADU: 1) the age of the
house, 2) the minimum oor area, and 3) the lot size.
Age of the house. Fourteen of the 37 municipalities that allow
ADUs to be rented out (not just occupied by relatives of the
homeowner), restrict the houses that qualify to have ADUs
created based on the age of the house. Some restrictions on the
age of the house signicantly reduce the number of qualifying
houses, while others principally prohibit ADUs in brand-new
construction. For example, Wayland’s and Concord’s bylaws
require that houses must have existed for at least two years;
Marsheld’s says three years; Newton’s four. In other munic-
ipalities, like Duxbury, Hamilton, Lincoln, Cohasset, and
not qualify, and the town rarely gets any applications. In Ded-
ham, ADUs can be added to houses where the lot is 10 per-
cent bigger than the minimum lot size, but most of the houses
in town are on non-conforming lots, smaller than the zoning
requires. Dedham has more than 6,000 single family houses,
but the town receives only a few applications per year to add
ADUs. Like Manchester and Dedham, 16 of the 37 munici-
palities that allow ADUs limit them to houses on lots bigger
than a certain size. In Duxbury and Wenham, the lot needs to
be 20,000 square feet, or almost a half-acre.
In Medeld, ADUs are allowed, but only in houses built
before 1938 that have a minimum oor area of 2,000 square
feet. In Burlington, ADUs are allowed in houses that had
at least 1,800 square feet of oor area as of 1989. Before the
1990s, most new houses were not that big; the median size
of new single family houses in the Northeast did not surpass
1,800 square feet until 1987, and didn’t top 2,000 square feet
until 1992. In Weston, ADUs are only allowed in houses that
have at least 3,000 square feet.
Belmont allows ADUs only in detached historic structures
such as antique carriage houses. Most houses lack historic
accessory buildings.
Owner Occupancy
In general, ADU regulations specify that the single-family
house must be occupied by the owner or owners. Many of the
requirements include the language, “except for bona de tem-
porary absences.” Some requirements get more specic about
owners being absent. In Lexington, absences of up to two
years are allowed:
An owner of a property containing an accessory apart-
ment who is to be absent for a period of less than two
years may rent the owner's unit as well as the second
unit during the temporary absence provided: a. Written
notice thereof shall be made to the Building Commis-
sioner on a form prescribed by him. b. e owner shall
be resident on the property for at least two years prior to
and between such absences.
In Hudson, Bedford, and Burlington, the owner/s can be
absent up to six months; in Manchester and Medeld, one
year. In Wayland, the owner can be absent one or two years:
e owner may be absent for periods not exceeding one
year, provided that no one occupies the owner's unit,
except a house sitter paying no rent. e owner's unit
may be rented for periods not exceeding two years, pro-
vided that prior written notice is given to the Building
Commissioner, the owners have occupied their unit for
the prior two years, and occupy for two years between
rental periods, and the owners remain legal residents of
the Town.
9
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Caps on ADU Production
Seven municipalities cap the number of ADUs that could be
added, either in general or over a certain period of time:
Hamilton: No more than 10 permits for ADUs can be
issued in any 12-month period.
Dover: No more than 10 percent of single-family homes can
have ADUs.
Cohasset: No more than 10 percent of single-family homes
can have ADUs, and no more than 10 permits can be issued
annually.
Carlisle: No more than 75 permits for ADUs can be issued.
Sudbury and Southborough: No more than 5 percent of
single-family houses can have ADUs.
Westwood: Permits for ADUs shall not exceed 2 percent of
the number of single-family and two-family houses.
Restrictions that Relate to the Accessory Units
Themselves (As Opposed to the Single-Family House
or Lot or Location)
Parking. Most municipalities require one o-street parking
space for an ADU. A few of the regulations vaguely speci-
fy that adequate o-street parking should be provided. Bed-
ford, Burlington, Hudson, Manchester, Stow, and Waltham
require two o-street spaces for the ADU. Cohasset requires
one space per bedroom. Scituate requires two spaces, but the
requirement can be waived to one space. Newton is the only
municipality that specically requires no additional o-street
parking for the ADU.
Bedrooms. Fifteen of the municipalities regulate the num-
ber of bedrooms that can be in an ADU. e most frequent
requirement is no more than two bedrooms. In Acton, ADUs
included in the same building as the primary dwelling unit
can have no more than two bedrooms, but ADUs in detached
structures can have three bedrooms. In Carlisle, on lots less
than three acres, the maximum number of bedrooms in an
ADU is two. In Littleton, ADUs can have no more than two
bedrooms, except by special permit. For ADUs attached to the
primary dwelling in Hamilton and Ipswich, there can be no
more than one bedroom.
Number of Occupants. Six municipalities limit the number of
ADU occupants. Dedham and Waltham limit them to two
occupants. Hudson, Reading, and Swampscott limit occupan-
cy to three people. Sudbury limits occupancy to four people.
Newton does not limit the number of occupants in an
ADU per se, but “the total combined number of individuals
residing in the principal and accessory dwelling units may
not exceed the number allowed in the principal dwelling
unit alone.” Occupancy of single family houses in Newton is
Weston, the house must have existed for 10 years. In Waltham
and Dedham, it must have been in existence when the subsec-
tion of the ordinance or bylaw was adopted.
Others are more restrictive. In Stow, ADUs can be added
to single-family houses or detached accessory structures that
were built by 1991. In Dover, the house must have been built
by 1985; In Manchester, 1984. In Medeld, the house must
have been in existence prior to 1938.
Minimum oor area. Another way of restricting houses that
qualify to have ADUs added is to require a minimum oor
area for the house. In Cohasset, the house must be at least
1,200 square feet. In Bedford and Cambridge, it must have
at least 1,800 square feet. In Burlington, the house must have
been 1,800 square feet as of 1989. e median size of new
single family houses in the Northeast did not become greater
than 1,800 square feet until 1987.
1
In Medeld and Canton,
the house must be at least 2,000 square feet. In Weston, the
house must have 3,000 square feet of oor area.
Lot size. e third way municipalities restrict the properties
that can qualify for ADUs relates to the size of the lot the
house is on. Sixteen of the 37 municipalities have such restric-
tions.
In all districts of Manchester except one, the lot size needs
to be twice the minimum lot size listed for single-family
houses in the zoning bylaw.
In Dedham, the lot needs to be 10 percent greater than the
minimum lot area of the district.
In Ipswich, ADUs can be added to non-conforming lots
(smaller than zoning requires for single family houses) if the
lot is bigger than 15,000 square feet.
In Medeld and Weston, the lot needs to meet the minimum
lot area requirements.
In Carlisle, the lot needs to be at least two acres, unless the
ADU’s occupancy gets restricted to low-income residents,
in which case there is no listed minimum lot size.
In Stow, ADUs are allowed by right if the lot is bigger than
1.5 acres, and by special permit for smaller lots.
In Concord, the lot must be at least 10,000 square feet.
In Canton, the lot must be at least 10,000 square feet, or the
minimum lot size for the district, whichever is greater.
In Duxbury, the lot must be 20,000 square feet.
In Wenham, the lot must be 20,000 square feet excluding
wetlands and oodplain, and for ADUs in a detached
structure, the lot must be 40,000 square feet, excluding
wetlands and oodplain.
1. Median and Average Square Feet of Floor Area in New Sin-
gle-Family Houses Completed by Location https://www.census.
gov/const/C25Ann/sftotalmedavgsqft.pdf
10
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
structures. Carlisle and Newton, for example, revised zoning
in 2017 to allow ADUs in detached structures.
Sixteen municipalities now allow ADUs in detached
structures. Some, like Weston, allow detached ADUs only in
a pre-existing structure such as a garage, barn, or gatehouse.
Belmont does not allow ADUs within the single-family
house, but allows them in historic structures. Municipalities
such as Newton and Lexington allow new construction of
detached ADUs. In Sudbury, the detached structure needs to
have existed for at least ve years.
Detached ADUs are allowed in Acton, Dedham, Hamilton,
Newton, Scituate, Stow, Wenham, Canton, Belmont, Lex-
ington, Littleton, Weston, Hudson, Sudbury, Ipswich, and
Carlisle.
By Right Versus By Special Permit
Most municipalities require special permits for ADUs. Acton,
Bolton, Burlington, Lexington, Littleton, Newton, Reading,
Stow, Wilmington, and Bedford allow ADUs by right, at least
in some circumstances. Some of those municipalities require
special permits for detached ADUs, larger ADUs, or ADUs in
certain districts. Rockport allows them by right in the down-
town district, but otherwise by special permit.
Many the municipal master plans and housing production
plans recommend that the municipality consider allowing
ADUs by right, instead of by special permit. In general, spe-
cial permits can create a barrier to development, where prop-
erty owners decide not to risk time and money on a permitting
process that might not yield a permit.
To assess how discretionary the special permits are, the
researcher asked if any applications have been rejected in the
last ve years, and for what reasons. Many municipalities did
not reject any. In every case except one, those that did said
the application did not comply with written requirements. For
example, the unit was detached from the main structure where
that is not allowed, or it did not meet specied dimensional
requirements. e only municipality where planners indicat-
ed any discretion in the process for special permits was New-
ton. Recently, Newton received two applications for detached
units that met the written requirements, but one application
was granted a special permit and the other was not. Neighbors
showed up to oppose the ADU application that got rejected.
In Newton, the Special Permit Granting Authority is the
City Council, so the process for approving special permits
can be particularly political. According to the 2004 study, the
special permit granting authority for ADUs is typically the
Zoning Board of Appeals. In 2004, 81 municipalities had des-
ignated the ZBA as the SPGA, 14 designated the planning
board, and Newton and Peabody designated City Council.
Another issue with special permits is that they take more
sta time to process. If a municipality receives few applica-
tions, that time might not be a critical factor. But the special
limited to one family and three unrelated individuals. In theo-
ry, a single person might live in the primary house and rent the
ADU to a large family.
Maximum Floor Area. More than half the municipalities lim-
it the maximum oor area of accessory dwelling units. e
most common limit is 900 square feet, in Cambridge, Cohas-
set, Dover, Hamilton, Hudson, Ipswich, and Westwood. e
smallest limit is 700 square feet in Stow. Acton and Swamp-
scott limit to 800 square feet, but Acton allows up to 2,000
square feet for ADUs in detached structures. Duxbury and
Sudbury limit to 850 square feet. e second most common
limit is 1,000 square feet, in Dedham, Newton, Lexington,
Reading, and Wenham. Newton allows up to 1,200 square
feet in ADUs within the house by special permit, and up to
1,500 square feet for ADUs in detached structures. Lexington
also grants special permits for bigger ADUs, up to 40 percent
of the house’s oor area. Lincoln, Littleton, and Carlisle allow
up to 1,200 square feet, and Wilmington allows 1,250.
Percent of Floor Area. Most municipalities also restrict the
oor area of the ADU as a percent of oor area of the house.
e most common requirements are in the range of 30-to-35
percent of the gross oor area. In Hamilton, an ADU cannot
cover more than 15 percent of the gross oor area. In Cohas-
set, Dover, Hudson, Ipswich, Southborough, and Weston, the
maximum is 25 percent. Littleton and Marsheld allow up to
40 percent. Acton allows for ADUs to take up half the oor
area. Carlisle allows up to 50 percent only for ADUs that are
restricted to low-income occupants; otherwise the ADU can-
not be more than 35 percent of the house.
Expansion. Several municipalities restrict how much a house
can be expanded to accommodate an ADU. In Reading,
ADUs are permitted by right as long as there is no expansion
of the house, but homeowners can apply for a special permit to
expand the house for an ADU. In Duxbury, the house cannot
be expanded for an ADU: “e accessory apartment does not
require alteration or addition to the single family dwelling in
such a manner that there is any exterior change to the dwell-
ing, so that the accessory apartment is located wholly within
the building footprint in existence at the time of the special
permit application.” In Ipswich, the house’s footprint can only
be expanded by 25 percent or 500 square feet, whichever is
less, on non-conforming lots. In Manchester and Medeld,
the house can be expanded up to 10 percent; in Wayland, 20
percent; in Littleton 15 percent.
Detached ADUs
Many municipal master plans have recommended that the
city or town allow ADUs in detached structures, and sever-
al have recently amended zoning to allow ADUs in detached
11
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Some building inspectors in municipalities that do not
allow ADUs mentioned that they permit ADUs as part of the
single-family house, because a single family house can have
multiple kitchens, per the building code.
Permitting Numbers
e survey of local planners and inspectors includes a question
about how many ADUs their municipality has permitted in
each of the last three years. Based on responses thus far, 2.5
units on average are permitted annually per municipality that
allows ADUs (including those that are restricted to relatives).
ree municipalities reported permitting as many as 12 or 15
in a single year.
e survey also asks the total number of ADUs that have
been permitted town-wide, or city-wide. e answers are
mostly in the range of 20 to 60. Scituate and Ipswich are each
at 100 total and Marsheld might have 150.
e appendix includes a chart of permitting numbers
reported in the survey.
Fourteen of the municipalities that provided annual per-
mitting data allow ADUs with residency restrictions (such
that only a relative of the homeowner or caretaker can live in
the ADU), and 20 of the municipalities that provided annual
permitting data allow ADUs without residency restrictions
(such that the ADU can be rented out). e 14 municipalities
with residency restrictions (‘family dwelling units’) on average
permitted ve units per municipality for the three-year peri-
od. e 20 municipalities without residency restrictions aver-
aged nine permitted units per municipality over three years.
e dierence in permitting levels holds when controlling
for the number of single-family houses (both detached and
attached because the U.S. Census includes townhouses in its
single-family house denition). e municipalities with resi-
dency restrictions granted one permit for every 1,000 houses
during the three-year period. e municipalities without res-
idency restrictions granted 1.8 permits for every 1,000 houses
during the three years. Across all municipalities that reported
permitting ADUs, with or without residency restrictions, the
rate was 1.4 permits granted per 1,000 single-family residenc-
es in those municipalities over the three-year period.
Carlisle saw an uptick in applications after a 2017 revision.
Newton and Lexington also received more applications after
revising their laws. Newton permitted eight units in the rst
ve months of 2018.
If the region were to allow ADUs more liberally, how many
rentals could be expected to be added? Could the region aver-
age ve per municipality per year for the 100 municipalities?
Over a decade, that would mean ve thousand new rentals, on
less than one in 100 properties with single family houses.
permit process could become burdensome for those that receive
a dozen or more. In Newton, by right permits for ADUs take
approximately eight hours of sta time total to process, while
special permits average about 25 hours of sta time.
In-Law Apartments
irty-one municipalities allow ADUs as long as residency is
restricted to relatives, caregivers, or in a few cases, people with
low incomes. It can be hard for the municipality to enforce the
residency restrictions.
Some comments by planners and building inspectors:
“ey are supposed to be for family members or for care-
givers, and we don’t really have a process for keeping up cer-
tication that a family member is using the unit. We are dis-
cussing a process to register the information.”
“One of our internal challenges is that when you get the
special permit it is for three years and it is renewable every
three years. Many people don’t renew, and they don’t realize
that they have to renew.”
“Inadvertently, I can guarantee, they turn into rentals.
ey are intended to be converted back to normal living space.”
Short Term Rentals (Like Airbnb)
In Bedford there was recently a case of an ADU listed on
Airbnb or a similar site. e town bylaw reads “ere shall
be no boarders or lodgers within either unit of a dwelling
with an accessory apartment.” e same wording is in Bur-
lington and Canton’s bylaws. Newton’s ordinance requires a
minimum occupancy or rental term of 30 days. A couple of
planners mentioned that the planning board will simultane-
ously address reforms to the ADU regulation and regulation
of short-term rentals.
Municipalities with No Zoning For Adus
irty-two municipalities have no provisions for ADUs. In
Arlington, a bylaw was proposed to Town Meeting in 2012,
but did not pass. Marblehead’s planning board is now con-
sidering the matter, and it will likely go to Town Meeting in
2019. In Somerville, the lowest-density residential districts
allow two-family houses, but the city is thinking about allow-
ing ADUs as well; they could be put on properties that do not
meet the requirements for a two-family house. Some of the
municipalities that do not allow ADUs do allow two-family
houses, at least in some districts.
12
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
No residency restrictions: Occupancy of the ADUs should not
be restricted to caretakers or relatives of the homeowner. It
is hard to enforce the restriction, and the region needs rental
housing. When units are legally rentable, the building inspec-
tors can make sure the housing is safe. Secret apartments do
not get the review that legal ones get.
Houses/properties that qualify: By restricting ADUs to large
older houses on large lots, cities and towns reduce the universe
of properties that qualify to have ADUs added. Requirements
for large lots can mean that houses built in the era of new rail-
roads and streetcars, when lots were narrow to maximize the
number of people living within walking distance of transit, do
not qualify. Ideally, many ADUs would be added in railroad
and streetcar-era neighborhoods, because those are the neigh-
borhoods where residents can still walk to shops and public
transportation.
Detached ADUs: Many homeowners would prefer to put an
accessory apartment above a garage or in a new detached
structure, as opposed to adding it to the single-family house.
To signicantly increase production, it would be wise to allow
detached ADUs more liberally.
Parking: Requiring two o-street parking spaces per ADU is
excessive. It makes sense to have a exible policy for parking,
or not to require parking, as in Newton’s case.
Dimensional requirements: Less onerous requirements around
bedrooms, oor area, and other dimensional specications
translate to more ADUs being added, and more people housed
in them.
Recommendations
e adoption of less-restrictive municipal ADU bylaws and
ordinances has proven to be a very slow process. Planners and
housing advocates have been promoting ADUs as a solution to
the region’s housing crunch for decades. Almost half the local
master plans and housing production plans adopted in the last
decade have included recommendations to allow ADUs more
liberally. Still, only 37 out of 100 municipalities allow ADUs
to be added and rented out, and most of the municipalities sig-
nicantly restrict the universe of properties that could qualify
for an ADU.
Given how challenging it has proven to be to change local
laws and allow ADUs more liberally, state legislators could
consider allowing ADUs in single family houses, even where
local bylaws and ordinances lack the provisions. en local
planners and housing advocates could focus on even more dif-
cult challenges, such as zoning for multi-family housing.
In the absence of state legislation that would allow ADUs,
voters in cities and towns can make many revisions to their
local zoning bylaws and ordinances to allow more ADUs in
the region. Some aspects of the zoning they might consider
include:
By right versus special permit: Sometimes allowing ADUs
only by special permit reassures local voters that each case
will be carefully reviewed and there will be opportunities for
neighbors to get involved when an ADU project appears inap-
propriate to them. If the choice is between allowing ADUs
by special permit or prohibiting them, special permits are the
better option. Special permits, however, might be seen by
homeowners as too risky to bother with, even if in practice
the permitting boards (typically the ZBA) grant permits to
all projects that meet the regulatory requirements. Moreover,
by-right permitting takes less sta time.
13
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Appendix
While some of the permitting numbers collected in the research are exact, others numbers pro-
vided represent vague estimates. (Note that “By Right” here means that at least some kinds of
ADUs in some part of the municipality are allowed by right. For example, in one district the use
might be by right, while it is by special permit in other districts.)
Municipality By Right or
Special Permit
Residency
Restrictions?
Three Years of Permits
(2017, 2016, 2015, unless
otherwise specified)
Total Permitted Comments
Acton By Right No 1 or 2 in 2016, other years
not reported
Ashland By Right Yes 0,1,0 (2016, 2015, 2014) Not tracked
Bedford By Right No 1,2,0 56
Bellingham By Special Permit Yes 18
*
,4,3 (2016, 2015, 2014)
*
mostly renewals
60
Belmont By Special Permit No 0,1,1 (2016, 2015, 2014)
Beverly By Special Permit Yes 0,0,0 ”I would guess
fewer than 25“
Boxborough By Right Yes 0,0,0 4 ”Never reached the five-per-year
limit.“
Carlisle By Special Permit No 8,1,1 24 ”Probably in the last three years
there have been ten. Most of those
in the last year. Before that, we were
averaging one per year, or less.“
Concord By Special Permit No 5,2,5 (2016, 2015, 2014) Unknown ”The [total] number is believed to be
fairly constant because the permits
for accessory dwelling units are
tied not to the property, but to the
owner.“
Dedham By Special Permit No Two to five per year ”If I were to make a
guess“: 25 to 30
Dover By Special Permit No 0,0,0 (2016, 2015, 2014) ”Very few“
Foxborough By Right Yes 2,2,5 (2016, 2015, 2014) 45
Franklin
*
By Special Permit Yes 5,5,5 (2016, 2015, 2014) Estimates 45
*
Franklin is a special case. It does
not have an ADU bylaw, but ADUs
restricted to relatives get permitted
under provisions for two-family
conversion.
Halifax
*
By Special Permit Yes 1,3,3 (2016, 2015, 2014) Approximately 46
*
Halifax is not in the MAPC region,
but data collected from it
Hamilton By Special Permit No 2,0,0 (2016, 2015, 2014)
Holliston By Right Yes 0,1,1 Not tracked; ”Fewer
than 30?“ ”Yes“
Hopkinton By Special Permit Yes 1,3,2 More than 30 Researcher suggested ranges, 1–10,
11–30, 31–100, more than 100.
“31–100”
Hudson By Special Permit No 3,1,0 (2016, 2015, 2014) “Would take too
much time to
delve into”
14
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Ipswich By Special Permit No 6,12,5 101 (76 in single
family houses,
25 in detached
structures.)
Lexington By Right No 3,5,6 (approximately) Less than
a hundred
Started tracking the permits in 2015.
“Back in the day we did an amnesty
program for illegal apartments.“ The
amnesty program brought in about
90 apartments out of an estimated
200. Those apartments would not all
qualify under the current provisions,
but were permitted as ”pre-existing.“
The town does not know how many
of the 90 currently exist. Some have
been decommissioned, but the
homeowner is not required to report
the removal of an ADU to the town.
Lincoln By Special Permit No 0,2,1 (2016, 2015, 2014) Approximately
57 to 67
Littleton By Right No 1,2,2 67 (31 expired)
Manchester By Special Permit No 0,0,0 ”Very rare“ ”Unsure of the number without
doing considerable research.“
Marshfield By Special Permit No ”Average 15 per year.“ ”We are probably in
the 150 range.“
Maynard By Special Permit Yes Approximately two permits
every three years.
”No current way of
knowing“
Medfield By Special Permit No Maybe six units in the last
three years, all family units
The town permits both family units
and ADUs. ADUs are only allowed
in pre-1938 buildings, bigger than a
certain size. Nobody has applied to
add an ADU, only family apartments.
Medway By Special Permit Yes 4,2,1 27
Melrose By Special Permit Yes 2,2,1 20
Milton By Special Permit Yes “Not more than
one per year”
Newton By Right No 9,5,7 44 confirmed. The permitting database goes back
to 2005. They are scanning old files
now.
Norwell By Special Permit Yes “My guess is one or none.”
Scituate By Right No 98
Stoneham By Special Permit Yes 6,5,1 50 to 60 There have been 50 – 60 approvals,
but the special permit is no longer
valid when the family member
moves out, so not all of those units
are currently permitted.
Swampscott By Special Permit No 0,0,1 5 to 10
Wenham By Special Permit No 3,2,0 24 as of 2008
Westwood By Special Permit No At least 45.
Wilmington By Right No 0,6,12 The 2001 Master Plan mentions
27 permitted ADUs.
15
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
e following lists are up-to-date as of the time the zoning was reviewed by the researcher during
2017 and 2018. In some cases, the zoning might have been amended in the time period between
the data collection and publication of the paper. For example, municipalities surveyed in the fall
of 2017 might have amended their zoning at Town Meeting in the spring of 2018, and the change
would not be reected here.
Municipalities that allow ADUs without restricting occupancy to relatives of the homeowner:
Acton
Bedford
Belmont
Bolton
Burlington
Cambridge
Canton
Carlisle
Cohasset
Concord
Dedham
Dover
Duxbury
Hamilton
Hudson
Ipswich
Lexington
Lincoln
Littleton
Manchester
Marsheld
Medeld
Milford
Newton
Reading
Rockport
Scituate
Southborough
Stow
Sudbury
Swampscott
Waltham
Wayland
Wenham
Weston
Westwood
Wilmington
Municipalities that allow ADUs but restrict residency to relatives of the homeowner, caretakers,
elderly people, or qualifying low-income households.
Ashland
Bellingham
Beverly
Boxborough
Brookline
Danvers
Foxborough
Gloucester
Hanover
Holbrook
Holliston
Hopkinton
Lynneld
Maynard
Medway
Melrose
Millis
Milton
Norwell
Peabody
Pembroke
Randolph
Rockland
Sharon
Sherborn
Stoneham
Stoughton
Tops eld
Wakeeld
Walpole
Weymouth
16
THE STATE OF ZONING FOR ACCESSORY DWELLING UNITS
Arlington
Braintree
Chelsea
Essex
Everett
Framingham
Franklin
Hingham
Hull
Lynn
Malden
Marblehead
Marlborough
Medford
Middleton
Nahant
Municipalities that lack zoning for ADUs (although in some of the municipalities, building
inspectors do grant permits for ADUs):
Natick
Needham
Norfolk
North Reading
Norwood
Quincy
Revere
Salem
Saugus
Somerville
Watertown
Wellesley
Winchester
Winthrop
Woburn
Wrentham
17
PIONEER INSTITUTE
About Pioneer
Pioneer Institute is an independent, non-partisan, privately
funded research organization that seeks to improve the quality
of life in Massachusetts through civic discourse and intellectu-
ally rigorous, data-driven public policy solutions based on free
market principles, individual liberty and responsibility, and the
ideal of eective, limited and accountable government.
About the Author
Amy Dain is currently conducting a study of residential
zoning regulation in Greater Boston, commissioned by
the Massachusetts Smart Growth Alliance. Previously she
coordinated the StatNet initiative for the Collins Center
for Public Management at UMass Boston, and managed
Pioneer Institute's Housing and Middle Cities Initiatives.
She earned her Master of Public Policy from the Harvard
Kennedy School of Government and Bachelor of Arts in
Russian Studies from Wesleyan University.
