Lexington, MA
Lexington, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 7/10
Last updated: 11/4/2025
Image source: Yankee Magazine
What You Need To Know
Lexington, 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. There are two pathways to building an ADU in Lexington. A Protected Use Accessory Dwelling Unit (PADU) and an Accessory Apartment are the two pathways to building. Each has specific regulations associated with it and are detailed below.
Type of ADU Permit Required
A PADU does not require a special permit and can be built using a traditional building permit, while an accessory apartment requires a special permit.
ADU Rules
Protected Use ADU Regulations:
An ADU can be maximum 900 square feet, or half the Gross Floor Area of the main house; whichever is smaller.
There are no minimum lot size requirements for building an ADU.
ADUs can be rented, but may not be able to be rented short-term.
The property owners are not required to live on site.
The property owners are allowed to build one ADU on their property.
The ADU may be attached or detached to the primary dwelling.
One additional parking space (on-street or off-street) is required if the property is further than 0.5 miles from a transit station.
General requirements for Accessory Apartments in Lexington:
There is only one ADU permitted per lot.
The owner of the main house must live in either the primary dwelling or the ADU.
If the owner is away from the property for less than two years, both the main house and ADU may be rented as long as:
Notice is given to the Building Commissioner
The owner must reside on the property at least two years before and after such leave
The ADU must be have a similar architectural style to the single family dwelling and meet the following criteria:
No exterior stairways.
Only one door can have the appearance of a principal entrance.
Lexington distinguishes between three different ADUs
Basic ADU
Maximum of 1,000 square feet for gross floor area
There cannot be greater than two bedrooms
The ADU must be located in the main house
Expanded ADU
The gross floor area cannot be greater than 40% of the gross floor area of the main house
The ADU is designed so that it is consistent with the appearance of a single family home
The ADU must be located in the main house
Accessory Structure ADU
This is an ADU in an accessory structure, i.e. a garage
Maximum of 1,000 square feet for gross floor area
The ADU is designed to have a similar architectural style of the single family home on that lot and surrounding lots
Resources:
https://www.lexingtonma.gov/2226/Accessory-Dwelling-Units-ADUs
https://www.lexingtonma.gov/DocumentCenter/View/14679/760-CMR-7100-Protected-Use-ADUs---Final
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
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
Brewster, MA
Brewster, MA Accessory Dwelling Unit (ADU) Rules
As of 12.08/2025
What you need to know:
Brewster, 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. The rules for Brewster are outlined below.
Type of ADU permit required:
ADUs in Brewster 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
An ADU can be a maximum of 1,000 square feet.
ADUs can be attached, detached, or built within the main house.
Properties within ½ mile of a transit station do not require additional parking. Properties outside of that area require one additional off-street parking spot.
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 an ADU in Brewster is ten months.
The ADU must have a similar architectural style to the main house.
The main house and the ADU must be owned by the same person(s).
Resources:
Warwick, MA
Warwick, MA Accessory Dwelling Units (ADU) Rules
Updated: 11/17/2025 - Rules still being finalized
What you need to know:
Warwick, 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. The rules for Warwick are outlined below.
Type of Permit Required:
ADUs in Warwick 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 in Warwick:
An ADU can be up to 900 square feet in Warwick.
ADUs may be attached, detached, or built within the main house.
Short-term rentals are allowed in either the main house or the ADU, but not both simultaneously.
Properties with an ADU may require additional off-street parking (driveway or garage).
Resources:
https://warwickma.org/wp-content/uploads/2024/12/2024-12-09-STM-Minutes-Complete.pdf
Shutesbury, MA
Shutesbury revised its rules for Accessory Dwelling Units in 2008 to make it easier for homeowners to add an additional dwelling unit to their properties. The city sees ADUs as a great to way help 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)!
Shutesbury, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 7/10 (10 is most accepting)
What you need to know:
Shutesbury revised its rules for Accessory Dwelling Units in 2008 to make it easier for homeowners to add an additional dwelling unit to their properties. The city sees ADUs as a great to way help 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)!
Type of Permit Required:
Shutesbury allows both attached and detached ADUs by right with a site plan review by the Zoning Board of Appeals.
ADU rules in Shutebury:
The property must have slightly more than 1 acre (45,000 SF, 1.03 acres).
The primary home and proposed ADU must follow the district’s setback requirements.
One of the two dwelling units must be owner occupied.
An ADU can only be added to a single family property.
No additional curb cuts can be created. Access to the ADU must be provided from an existing driveway or access road to the property.
See the full text here: Zoning Ordinance, Section: 4.4-2 Accessory Apartments
Plainfield, MA
Plainfield loves ADUs and has a favorable permitting process. However, it is important to note that the town’s rules are very clear that the design and site plan must conform with the single family and rural characteristics of the town.
Plainfield, MA Accessory Dwelling Units (ADU) Rules
City Acceptance Rating: 9/10 (10 is most accepting)
What you need to know:
Plainfield loves ADUs and has a favorable permitting process. However, it is important to note that the town’s rules are very clear that the design and site plan must conform with the single family and rural characteristics of the town.
Plainfield also provides guidelines to convert a single family property to a multi-family property. If homeowners use this approach to add an additional apartment getting financing will be easier and they will maximize their home’s value. Multi-family conversions can only use existing space in the single family home (no additions or construction).
Type of Permit Required:
Plainfield allows both attached and detached accessory dwelling units (ADUs) to be built by right.
If a lot is nonconforming, an ADU requires a special permit.
ADU rules in Plainfield:
An ADU can be added to either a single or two-family dwelling.
It must be a fully separate living space including its own kitchen, bath, and egress.
Only one Accessory Apartment can be added to a residential lot.
The lot in question must conform to its zoning district’s rules (e.g size and street frontage).
The ADU and site plan must maintain the residential and rural character of the neighborhood. Exterior modification, including new detached structures must match the existing architectural elements of the home.
New entrances shall be located facing the side or front yard of the lot.
Adding an ADU to an original building or a backyard ADU is permissible as long as it is subordinate to the dwelling.
ADUs can not be larger than one third (33%) of the existing residential living space or nine hundred (900) square feet, whichever is less.
Off-street parking spaces must conform to the schedule in Section 5.3.
A sanitarian or professional engineer, registered in the Commonwealth of Massachusetts, must certify that the sewage disposal system can accommodate the additional apartment.
Read the full bylaw here: Zoning Ordinance, Section 8.2 Accessory Apartments and Multi-family Conversions
Pelham, MA
Detached ADUs are only allowed by Special Permit in its Village Center Districts. Conversion of existing space or additions are only allowed by right in its Village Center Districts.
Pelham, MA Accessory Dwelling Units (ADU) Rules
City Acceptance Rating: 5/10 (10 is most accepting)
What you need to know:
Pelham’s ADU rules differ per zoning district, so it is important to know which district your property is located in.
Type of permit required:
Detached ADUs are only allowed by Special Permit in its Village Center Districts.
Conversion of existing space or additions are only allowed by right in its Village Center Districts.
See the Village Center Zoning Districts
ADU rules in Pelham:
Act as a fully separate living unit with a kitchen, bathroom, and its own means of egress.
Only one accessory apartment is allowed per lot.
No more than three persons shall occupy the accessory apartment.
One of the two units must be owner occupied. When the owner(s) is not living on the property the ADU must remain vacant.
The ADU must be designed to match the character of the existing house and neighborhood. New entrances shall be located on the side or rear of the building.
The ADU shall be clearly subordinate to the primary dwelling.
The ADU cannot have more than two bedrooms and the maximum living area is 800 square feet or 1/3 of existing living space, whichever is less.
The lot must have at least three, permanent off-street parking spaces. These parking spaces shall be screened from road ways and adjacent or abutting properties with dense, hardy, evergreen plantings, earthen berms, walls or tight fence, complemented by evergreen plantings or other decorative elements.
The well and existing sewage disposal system must be reviewed by the board of health before a special construction permit is issued.
The Zoning Board of Appeals reserves the right to grant variance from these rules to encourage the development of housing units for disabled and handicapped individuals and persons with limited mobility.
See the full text here: Zoning Ordinance Section 5, 125-9.1 Accessory Apartments
Palmer, MA
Palmer allows both attached and detached accessory dwelling units (ADUs) to be built by special permit. However, it is important to note that the town’s rules are very clear that the design and site plan must conform with the single family and rural characteristics of the town.
Palmer, MA Accessory Dwelling Units (ADU) Rules
City Acceptance Rating:
5/10 (10 is most accepting)
What you need to know:
Palmer allows both attached and detached accessory dwelling units (ADUs) to be built by special permit. However, it is important to note that the town’s rules are very clear that the design and site plan must conform with the single family and rural characteristics of the town.
Type of Permit Required:
Both attached and detached ADUs require a special permit.
ADUs used as rentals to non family members are not permitted in the Rural Residential District.
ADU rules in Palmer:
Requirements for all accessory dwelling units
If a home is being used as an ADU and as space to conduct business, the ADU must be occupied by family. The bylaw refers to this as “Home Occupation.”
Only one entrance door can be added to the new unit that faces the street.
Parking:
In the Village Center District, the zoning board of appeals may waive parking requirements if there is adequate public parking near the proposed unit.
One additional space is required if an ADU is being included in the construction of a new home.
The ADU living area may be no more than thirty-three percent (33%) of the living area of the house or 800SF whichever is less.
Rules for Detached & Additions
The exterior finish material must be the same or visually match that of the existing home.
The roof pitch must match that the existing home.
Trim must match that the existing home.
Windows must match that the existing home in proportion and orientation.
Eaves must project from the building walls the same distance as the eaves on the existing home.
Read the full bylaw here: Zoning Ordinance, Section 171-89 Accessory Dwelling Units
Montague, MA
Montague has very favorable rules related to backyard homes (ADUs). There are limited restrictions and their zoning bylaw overall does not place excessive regulations on what can be built on a someone’s land. Setback requirements are also some of the most accommodating in Western Mass. However, homeowners still need to apply for a special permit to build a detached ADU so it will be important to plan a project that considers neighbors and the public if your ADU will be visible from the street.
Montague, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 8/10 (10 is most accepting)
Evaluate your property:
What you need to know:
Montague has very favorable rules related to backyard homes (ADUs). There are limited restrictions and their zoning bylaw overall does not place excessive regulations on what can be built on a someone’s land. Setback requirements are also some of the most accommodating in Western Mass. However, homeowners still need to apply for a special permit to build a detached ADU so it will be important to plan a project that considers neighbors and the public if your ADU will be visible from the street.
Type of Permit Required:
Living Space Conversion:
Conversion of space within an existing home can be done with only a building permit.
Additions and Detached:
Both new additions, conversion of existing detached structures and newly constructed detached structures require a Special Permit.
ADU Rules in Montague:
Only one Accessory Apartment may be created on a single-family lot.
Utilities, water & sewer must be integrated with the single-family dwelling.
The owner must occupy either the ADU of primary home.
The ADU must maintain the single-family character of the home
The ADU’s design must match the character of the home
New entrances shall be located on the side or rear of the building.
New stairways to provide access or egress to the ADU shall be enclosed, screened, or located so they are not visible to the public.
A ADU cannot be larger that 900 SF
A minimum of two (2) off street parking space must be provided and the entire lot can not have more than 4.
Minimum lot size requirements are waved in districts AF-1, RS-2 and RB
The Building Inspector or the Zoning Board of Appeals may allow reasonable deviation from the stated conditions to accommodate features that facilitate access and mobility for disabled persons
See Dimensional Requirements (extracted12/14/2019)
See the full Zoning Ordinance here: Zoning Ordinance Section 8.5.2 Accessory Apartments
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
Great Barrington, MA
Great Barrington loves ADUs and allows them by right in all zoning districts. However, it is important to note that the backyard home cannot be greater than 650 SF. Additionally, if an ADU is proposed in an existing nonconforming structure, a special permit will be needed.
Great Barrington also defines a path to convert a single family property to a legal duplex or multifamily property. For eligible lots, this formal conversion will allow homeowners to maximize their property value. Duplexes and multifamily properties are discussed in section 8.1 and 8.3 of the zoning bylaw.
The town is also deliberating on new rules that would allow tiny homes on trailers! Stay tuned for more information and if you are a resident of Great Barrington contact the planning/zoning board to voice your support.
Great Barrington, MA Accessory Dwelling Units (ADU) Rules
City Acceptance Rating: 7/10 (10 is the most accepting)
What you need to know:
Great Barrington loves ADUs and allows them by right in all zoning districts. However, it is important to note that the backyard home cannot be greater than 900 SF. Additionally, if an ADU is proposed in an existing nonconforming structure, a special permit will be needed.
Great Barrington also defines a path to convert a single family property to a legal duplex or multifamily property. For eligible lots, this formal conversion will allow homeowners to maximize their property value. Duplexes and multifamily properties are discussed in section 8.1 and 8.3 of the zoning bylaw.
The town is also deliberating on new rules that would allow tiny homes on trailers! Stay tuned for more information and if you are a resident of Great Barrington contact the planning/zoning board to voice your support.
Type of Permit Required:
Great Barrington allows both attached and detached accessory dwelling units (ADUs) to be built by right.
If the ADU is proposed in a nonconforming lot, it requires a special permit.
ADU Rules in Great Barrington:
Only one ADU is allowed per lot.
ADUs are allowed on single family and two family lots.
The ADU and primary home must have the same owner.
The ADU cannot be larger than 900 gross square feet. (“Gross” includes unfinished space and area with low ceilings)
A newly constructed backyard home or addition must meet setback and other dimensional requirements related to the primary home. An ADU can be located in an existing nonconforming structure with a special permit.
The ADU must be provided one parking space. This spot must be in addition to the minimum required spaces for the primary home. The parking space must be located behind the front setback line, unless a variance is granted by the planning board.
When possible, new entrances to the ADU must be located on the rear or side of the building.
Fire escapes and outside stairways leading to a second or higher story shall be located on the rear or side of the building. They should not be visible from the street.
Read the full bylaws here:
Zoning Ordinance, Section 8.2 Accessory Dwelling Units
Zoning Ordinance, Section 8.1 Two-family residential use of a single lot.
Amherst, MA
In 2014, Amherst joined many cities in MA by revising bylaws making it easier for homeowners to install accessory apartments in all zoning districts. They have very straight forward rules in their zoning ordinance, but design requirements are strict and certain neighborhoods are harder to obtain approvals than others due to fears about student tenants and noise.
Amherst, Massachusetts Accessory Dwelling Unit (ADU) Rules
Updated: 12/05/2025
What you need to know:
Amherst, 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.
There are two types of ADUs allowed in Amherst - Protected Use ADUs (PADU) and Local ADUs. PADUs are generally in line with Massachusetts state law regarding ADU zoning and requirements, while Local ADUs have their own rules.
Type of Permit Required:
Protected Use ADUs in Amherst are considered by-right, meaning they are allowed in any single-family residential zoning district with a simple building permit.
Local ADUs require administrative approval if the lot has no existing PADU. If the lot already has a PADU, owners can apply for a special permit to build a Local ADU.
ADU Rules in Amherst:
General ADU Rules in Amherst:
No more than one Local ADU and one Protected Use ADU are allowed on the same lot as the main house.
ADUs can be attached, detached, or built within the main house.
Whenever possible, detached ADUs cannot be built closer to the road than the main house.
ADUs need to submit a parking plan to the Building Commissioner and have it approved.
The driveway can be altered or added to, but a new driveway to the street is not typically allowed.
No more than two off-street parking spaces can be added for any ADU.
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.
Storage of trash and recycling must be inside the interior of the ADU, in a garage or another accessory outbuilding.
All exterior lighting must be designed and installed to avoid disturbing neighboring properties.
If the owner wants to rent the ADU or their main house, it will have to be registered and permitted in accordance with the Residential Rental Property Bylaw (See here: https://www.amherstma.gov/DocumentCenter/View/24029/Residential-Rental-Property-Bylaw?bidId=).
ADUs shall not have a new driveway or curb cut unless approved by public works.
Protected Use ADU Rules in Amherst:
PADUs can be maximum 900 square feet, or half the Gross Floor Area of the main house; whichever is smaller.
There is no minimum lot size to build a PADU.
PADUs within ½ mile of a transit station do not require additional parking. Properties outside of that area could require additional off-street parking.
PADUs do not require owner-occupancy.
PADUs have less restrictive setback requirements than Local ADUs in Amherst.
Local ADU Rules in Amherst:
Local ADUs can be a maximum of 1200 square feet.
Local ADUs must have a similar architectural style as the main house.
Either the main house or the Local ADU must be occupied by the property owner(s).
Resources:
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
Chesterfield, MA
Chesterfield joined many cities in MA by revising its zoning bylaw to make it easier for homeowners to build accessory apartments in most zoning districts.
Chesterfield, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 7/10 (10 is most accepting)
What you need to know:
Chesterfield joined many cities in MA by revising its zoning bylaw to make it easier for homeowners to build accessory apartments in most zoning districts.
Type of Permit Required:
Conversion of Existing Space or Attached:
By right in:
Town Center
Agricultural Residential I
Agricultural Residential II
By Special Permit in the following overlay districts:
Floodplain
Westfield River Protection District
Water Supply Protection District
Special permits are also required if an apartment is being added to a commercial building.
Detached ADUs:
A Special Permit is always required for detached ADUs.
ADU Rules in Chesterfield:
The ADU must be a fully separate dwelling unit with its own kitchen, bath, and egress.
A lot can only have one accessory apartment.
The ADU must have 2 or fewer bedrooms.
At least two additional off-street parking spaces shall be provided for the ADU. Parking spaces shall be located on the side or rear of the building to the extent feasible.
The ADU’s appearance must match the character of the original building.
New entrances shall be located on the side or rear of the building to the extent feasible.
The ADU must be subordinate to the primary building.
The living area shall not be more than 33% of the existing residential living space (commercial building SF) or 800 square feet, whichever is less.
Small homes or commercial buildings, can bypass the 33% limitation and build a 300 square feet ADU.
Read the full bylaw here: Zoning Ordinance, Section 6.1 Accessory Apartments
Easthampton, MA
In 2014, Easthampton joined many cities in MA by revising its zoning bylaw to allow homeowners to build accessory apartments in all zoning districts. Installations started slow and have been used primarily for aging parents or to help care for disabled family members.
Today – surging home prices, high rents, and unwanted gentrification have put the bylaw in the spotlight and have stimulated demand for detached accessory dwelling units (Backyard ADUs).
Easthampton, MA Accessory Dwelling Unit (ADU) Rules
City Acceptance Rating: 9/10 (10 is most accepting)
What you need to know:
In 2021, Easthampton revised its zoning bylaw to allow homeowners to build accessory apartments in all zoning districts.
Type of ADU Permit Required:
A building permit is required and a special permit in some instances (we can help with this).
ADU Rules in Easthampton:
ADUs are allowed on lots with Single-Family or Two-Family Homes.
The owner(s) of the detached single- or two-family dwelling must occupy one of the units as their primary residence at the time of occupancy. (No longer in compliance with the MA state ADU law)
A new detached ADU (and/or an attached unit consisting of new construction) must not exceed 900 square feet.
One new off-street parking space is required for the ADU. The new parking space materials must be consistent with the existing driveway.
A waiver of this requirement may be granted for such reasons as, the resident has a disability or an occupant that does not own a vehicle.
If a new or expanded driveway is proposed within 10 feet of a side or rear lot line, a landscaped buffer of at least six feet—measured from the lot line—must be provided.
Within this buffer zone, no parking, storage, or other use is permitted unless a written agreement is created and submitted to the building department between the applicant and neighbor.
No more than one ADU on a lot.
The principal dwelling and the ADU must remain in common or single ownership.
For tax purposes, a second dwelling unit may be considered a two-family dwelling for tax purposes.
Interior and Attached ADU Rules
An interior or attached ADU is required to be designed to maintain the appearance of a single- or two-family dwelling with a separate entrance.
The separate entrance must be either outside or through a shared entry with the primary dwelling.
All stairways to the ADU above the first floor must be within the building. If constructed outside the building, the stairs cannot face the street.
Maximum height, minimum setbacks, and maximum building coverage for a primary dwelling must be met.
Detached ADU Rules
An existing accessory structure can be converted to an ADU as long as no changes in footprint or height are made.
Maximum height, minimum setbacks, and maximum building coverage for a primary dwelling must be met.
A new detached ADU cannot be greater than 900 square feet.
Easthampton Setbacks and Density Tables
See the full text here: Zoning Ordinance Section 8.5, Accessory Apartments, page 117