Cambridge, MA
Cambridge, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10
Last updated: 6.21.2024
Image source: USNews
What You Need To Know
ADUs are allowed in Cambridge in all zoning districts in structures in existence as of February 1st 2019. A single-family, two-family, or accessory structure may be altered to provide an ADU.
Type of ADU Permit Required
ADUs in Cambridge require a special permit.
ADU Rules in Cambridge
ADUs are only permitted in structures that have been in existence since on or before February, 1, 2019.
The principal residence must have at least 1,800 square feet of gross floor area.
The ADU is limited to 900 square feet or 35% of the gross floor area of the primary residence, whichever is less.
Only one ADU is permitted on any given lot.
A two-family home may be converted to a single family home with an ADU by right - no need for a special permit.
An ADU within or attached to an accessory structure cannot be greater than 900 square feet
The authority granting the special permit must determine that the appearance is compatible with the primary residence as well as the homes in the surrounding area.
For both ADUs within or attached to a principal residence and accessory structure
Special Permit Information
ADUs are not included in lot area per dwelling calculations.
The Board of Zoning Appeal may relax space requirements for ADUs built within structures; however, any gross floor area added must comply with ADU requirements.
To ensure a safe environment, setbacks and height restrictions may be altered.
EX: safe egress
Resources:
Cambridge Massachusetts Land Use Regulations- Article 4.20
Lincoln, MA
Lincoln, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10
Last updated: 6.21.2024
Image source: deCordova Sculpture Park and Museum
What You Need To Know
In Lincoln, ADUs are allowed both within a single family home as well as in a detached structure. Additionally, through the Affordable Accessory Apartment Program in Lincoln, ADUs are allowed under other guidelines, detailed below, with the intention of creating affordable housing to families and individuals whose income is between 60%-80% area median income. They emphasize a desire to serve populations such as families, single parents, veterans, seniors, town employees, and employees of small local businesses.
Type of ADU Permit Required
ADUs within an existing dwelling require a building permit whereas an ADU in an accessory structure, outside the main structure, or through the Affordable Accessory Apartment Program require a special permit.
ADU Rules
For ADUs not part of the Affordable Accessory Apartment Program:
ADUs (not part of the Affordable Accessory Apartment Program) are limited to 5% of the residential units in Lincoln.
The ADU is limited to 1,200 square feet
An ADU within a single family home cannot be greater than 35% of the floor area of the single family home and the ADU combined.
EX. 2,500 square foot single family home +1,200 square foot ADU = 3,700 square feet total x .35 = 1,295 square feet.
In this example, the ADU would have to be smaller.
An ADU is only permitted on lots that contain at least 40,000 square feet.
The owner of the property must own both the ADU and the single family home and live in either the ADU or the single family home.
For both building and special permits, dimensional floor plans and a site plan must be submitted showing the following:
Location, setbacks, height, and location of a parking space for the ADU
ADUs must meet setback and height requirements laid out in the zoning bylaw for primary structures or accessory structures depending on the location.
Provision for sewage must be made per the requirements of the Board of Health.
Proper ingress and egress as well as one parking space must be provided.
The primary residence must retain the appearance of a single family home.
If the ADU is rented, it must be rented for a minimum of seven days
ADUs through Lincoln’s Affordable Accessory Apartment Program are intended to:
Provide families and individuals whose income is between 60%-80% area median income (AMI) housing
Provide young families, single parents, veterans, seniors, town employees, and employees of small local businesses housing
Allow residents of Lincoln with modest income to get income that will allow them to stay in their homes
Add units to the Subsidized Housing Inventory at little cost to Lincoln
Spread affordable housing throughout Lincoln
Contribute to efficient use of land and structures in Lincoln
Add units without changing the footprint of the existing structure
Requirements
Special permit through the Zoning Board of Appeals
A deed restriction
This is a 15 year deed restriction recorded at the South Middlesex Registry of Deeds
The deed restriction ends if the property is sold
The deed restriction can be voluntarily terminated with 60 days notice at the end of a tenant’s lease
An affirmative fair marketing plan
This refers to the process of selecting tenants in a way that advances fair housing and equity.
Homeowners are required to select tenants from a waiting list generated by the Affordable Accessory Apartment Program
Family members or employees of the homeowner may not be a tenant through the Affordable Accessory Apartment Program
The home must retain the appearance of a single family home
The ADU will have a separate entrance
Off-street parking is available
The changes that are made must not be a detriment to the neighborhood
The ADU may not exceed 1,200 square feet or more than 35% of the home’s square footage
The septic system is adequate
The plans provided are certified by an architect
Homeowner Benefits
Homeowners qualify for a real estate tax exemption on the portion of property dedicated to an Affordable Accessory Apartment. Essentially, homeowners are not charged for the portion of property used for affordable housing purposes.
Zero interest loans totalling $25,000 over a ten year period will be granted to homeowners.
After ten years the loan is forgiven
Resources:
https://www.lincolntown.org/DocumentCenter/View/27060/Affordable-Accessory-Apartment-Program
Newton, MA
Newton, MA Accessory Dwelling Unit (ADU) Rules
Last Updated 11/18/2025
Image source: Kenneth C. Zirkel
What You Need To Know
Newton, like all of Massachusetts since the passage of the 2024 Affordable Homes Act, allows ADUs by right. Each town has slightly different rules surrounding ADUs, but they all must adhere to the framework outlined by the state. Newton has general ADU rules as well as specific rules for detached and internal ADUs. These rules are outlined below.
Type of ADU Permit Required
ADUs in Newton do not require special permits, and can be built using a traditional building permit. Residents are allowed to build one ADU per lot.
ADU Rules
General ADU Rules in Newton:
ADUs can be attached, detached, or built within the main house (internal).
ADUs must have a separate entrance from the main house.
Attached ADUs can share an entry hall with the main house, but need a separate entry within the entry hall.
Short-term rentals are not allowed. The minimum rental period for ADUs in Newton is 30 days.
The main house and ADU must be owned by the same person(s).
No more than 1 ADU is allowed per lot.
Detached ADU Rules in Newton:
Detached ADUs can be a maximum of 1,000 square feet, or half the Gross Floor Area of the main house; whichever is less.
You can apply for a special permit for a 1,500 square foot detached ADU with the City Council.
Internal ADU Rules in Newton:
Internal ADUs can be a maximum of 1,000 square feet, or half the Gross Floor Area of the main house; whichever is less.
You can apply for a special permit for a 1,200 square foot internal ADU with the City Council.
Resources:
https://www.newtonma.gov/home/showpublisheddocument/29823/638717834291930000
(See pages 132-135)
Provincetown, MA
Provincetown allows property owners to build new attached and detached dwelling units by right in all zoning districts except S (Seashore) and M (Public Use) districts.
Provincetown, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
Last updated: 6.6.2024
Image source: Frommers
What You Need To Know
ADU bylaws were recently updated in Provincetown. They now allow between two and four dwelling units on a single lot depending on your zoning district.
Type of ADU Permit Required
ADUs in Provincetown require a building permit, not a special permit.
ADU Rules
ADUs per lot are dependent on your residential district
Residential 1 Zoning District
No more than two dwelling units total
Residential 2 Zoning District
No more than three total dwelling units total
Residential 3, B, TCC, and GC Zoning Districts
No more than four dwelling units total
ADUs cannot be used for short term rentals. Must be rented for a period greater than 31 days.
Detached ADUs cannot be greater than 600 square feet.
40% of gross floor area if the ADU is located in the primary dwelling
Parking requirements do not apply to ADUs.
Resources:
Town of Provincetown Zoning By-laws- Page 29
https://www.provincetown-ma.gov/DocumentCenter/View/762/Zoning-By-Laws-PDF?bidId=
Mashpee, MA
Mashpee, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
Last updated: 6.18.2024
Image source: Mashpee Commons
What You Need To Know
Accessory dwelling units are referred to as ADUs in Mashpee.
Type of ADU Permit Required
A building permit is required for an ADU.
ADU Rules
The property owner must reside in either the primary dwelling or accessory dwelling unit.
It is possible to rent either the primary dwelling or the ADU; however, both cannot be rented at the same time. Rental period may not be less than 30 consecutive days.
Conservations commission, historic, and wastewater treatment requirements must be complied with.
ADUs can be up to 900 square feet and cannot be less than 350 square feet.
ADUs can be within or attached to the existing dwelling or detached.
There cannot be greater than two bedrooms in an ADU.
The design of the ADU must be consistent with the existing dwelling.
One off-street parking space must be provided for the ADU.
ADUs cannot have their own driveway as new curb cuts are not permitted.
Resources:
Zoning Bylaws of the Town of Mashpee, MA- Article 4/§174-45.4 A/Page 80
https://www.mashpeema.gov/sites/g/files/vyhlif3426/f/uploads/2023_zoning_bylaws_0.pdf
Orleans, MA
Orleans currently has restrictive rules associated with adding an ADU to a single family lot. The town does not allow additions or new construction unless it will have a minimal impact on the existing footprint of the existing structures.
Orleans, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
Last updated: 6.18.2024
Image source: Cape Cod Life
What You Need To Know
Orleans, like many other towns on Cape Cod, have made amendments to their zoning bylaws to combat the growing need in the area for affordable housing. Still, there remains a number of rules that must be complied with to build an ADU.
Type of ADU Permit Required
There are restrictions and guidelines, but ADUs are by right in Orleans and are approved by the building commissioner.
ADU Rules
The ADU cannot be greater than 800 square feet.
Additions cannot increase lot coverage by more than two percent of the lot area.
The lot must be at least 30,000 square feet of contiguous buildable upland.
One of the two units must be owner occupied year round.
The rental term must be at least 90 days.
Likely changes after vote in May:
The accessory dwelling shall contain no more 1,200 square feet of floor area.
The Board of Health must have documented to the Building Commissioner that sewage disposal will be satisfactorily provided for in accordance with the provisions of Title 5 and local Board of Health regulations, including provisions for an appropriate reserve area on the site.
There are no limitations on lot sizes.
The dwellings if leased shall be for periods of not less than ninety (90) days.
Resources:
Harwich, MA
Harwich, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
Last Updated: 6.18.2024
Image source: Winstead Inn
What You Need To Know
In Harwich, ADUs are referred to as Accessory Apartments. These structures can be within, attached, or detached from the primary dwelling.
Type of ADU Permit Required
ADUs or ADUs require a special permit.
ADU Rules
Only one ADU is permitted per primary dwelling.
The ADU and primary dwelling must have the same owner.
Either the primary dwelling or the ADU may be rented, but only one unit can be rented at a time.
The rental period is limited to at least six consecutive months.
There is a limit of 1,000 square feet of gross floor area for ADUs.
The ADU may not have greater than two bedrooms
There must be one parking space available for the ADU.
The ADU must be designed in such a way that the property retains the characteristics of a single family home.
All applicable zoning ordinances, setbacks, and sewer/septic regulations must be met.
Resources:
Eastham, MA
Eastham loves ADUs and thinks they can help them ease their housing crisis. As with many towns in the Cape they allow all kinds of ADUs by right!
Eastham, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating:
10/10 (10 is most accepting)
What you need to know
Eastham loves ADUs and thinks they can help them ease their housing crisis. As with many towns in the Cape they allow all kinds of ADUs by right!
Type of permit is required?
ADUs are only allowed in the following districts:
By Right:
District A (Residential), E (Residential/limited commercial), G (Water Resource Protection), Core Commercial, Transition Commercial, Office Residential, Limited Commercial
By Special Permit:
District F (seashore)
Not Allowed:
District B (Marina), H (Wellhead Protection), and Trade Park
ADU rules in Eastham:
Only one ADU is permitted on a single family lot.
The unit must be a fully separate living area with its own kitchen, bathroom and egress.
The ADU shall be clearly subordinate to the primary home.
An ADU shall be designed so that the property continues to look like a single family lot and the privacy of abutting properties is maintained.
The lot does not require a minimum acreage of buildable upland.
The Accessory Dwelling Unit (ADU) shall contain no more than two bedrooms.
The maximum size for an ADU is 1200 square feet or fifty percent of the site coverage of the principal dwelling, whichever is smaller. However, a Special Permit for an Accessory Dwelling Unit exceeding fifty percent site coverage rule can be issued.
At least one 1 off-street parking space is required for each Accessory Dwelling Unit (ADU).
The ADU and primary residence cannot be sold separately or divided into separate entities.
Either the primary dwelling or the ADU must be occupied on a year-round basis. Short term rentals cannot occur in both units.
See the full text here: Zoning Ordinance Section VII C. Accessory Dwelling Units
Greenfield, MA
Greenfield revised its rules for Accessory Dwelling Units in 2016 to make it easier for homeowners to add an additional dwelling unit to their properties. The city sees ADUs as a great to way increase density and create high quality housing without sacrificing the character of the town. Since the bylaw was approved, there have been many ADUs added to homes including at least one backyard home (detached ADU)!
Greenfield, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
What you need to know:
Greenfield revised its rules for Accessory Dwelling Units in 2020 to make it EXTREMELY easy for homeowners to add an additional dwelling unit to their properties. The city sees ADUs as a great to way increase density and create high quality housing without sacrificing the character of the town. Since the bylaw was approved, there have been many ADUs added to homes including at least one backyard home (detached ADU)!
ADUs can be added to two and single-family homes by right! This means there is no public hearing process and owners of two-family homes with landlord experience can add another unit.
Type of Permit Required:
Greenfield allows all types of ADUs by right. This included space conversion, detached ADUs, additions, and conversion of existing accessory structures (barns, garages, etc).
ADU Rules in Greenfield:
The additional unit must have its own kitchen, bathroom, and means of egress.
An ADU can be added to single-family and two-family properties.
One of the two dwellings must be owner-occupied.
The single-family character of the home must be retained and new entrances must be located on the side or rear of the house.
New detached structures or additions must match the character of the existing house.
Any stairways, access, or egress alterations serving the Accessory Dwelling Unit shall be hidden from public view.
The ADU can not be larger than 900 sq. ft. or one-third the total gross floor area of the home, whichever is greater.
Once built, the ADU cannot be enlarged beyond the square footage approved with the original permit.
An Accessory Dwelling Unit may not be occupied by more than three (3) people.
The ADU must have 2 or fewer bedrooms.
Detached ADUs are considered Accessory Structures and must follow rules as such.
The entire property must have at minimum 2 parking places and cannot have more than 4.
Septic system capacity must be validated by the Board of Health before a permit issued.
Deviations from the above can be granted to accommodate people with a disability and persons with limited mobility.
See the full text here: Zoning Ordinance Section 200-7.18. Accessory Dwelling Units, page 119
Northampton, MA
In 2014, Northampton joined many cities in MA by revising its zoning bylaw to make it easier for homeowners to build accessory apartments in all zoning districts. They have attractive rules in their zoning ordinance and biggest restrictions are related to environmental protections.
Northampton, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 10/10 (10 is most accepting)
Last updated: 7.22.2024
Source: City of Northampton
What You Need To Know
Northampton updated their ADU rules to allow for two single-family dwellings on one parcel in residential districts. In Northampton, they have removed ADU language from their rules and permit everything as a second dwelling on the same lot. Each district has specific requirements that must be met for the new dwelling unit.
Type of ADU Permit Required
Each additional single family dwelling (ADU) is subject to site plan approval by the planning board.
ADU Rules
Two single-family dwellings are allowed subject to site plan approval in the follow districts:
Rural Residential
Suburban Residential
Urban Residence A
Urban Residence B
Urban Residence C
Water Supply Protection
Farms Forest Rivers
Each zoning district has a specific lot area, open space, setback, and parking requirements for adding single family dwellings to a piece of land with an existing single family residence. Please connect with our team to see what is possible at your specific address!
Resources:
https://ecode360.com/13265306