Accessory Dwelling Units

An accessory dwelling unit is a small residential living space located on the same lot as another home. ADUs can play a significant role in our housing crisis. The ADU law allows property owners to build an ADU by-right.

ADUs can be inside an existing home, like converting a basement into an apartment, attached to a primary residence as an addition, or completely detached, like a cottage or converted garage in a backyard.

On Aug. 6, 2024, Governor Healey signed the Affordable Homes Act into law (Chapter 150 of the Acts of 2024). Section 8 of the Affordable Homes Act amends the Zoning Act (M.G.L. c. 40) to allow ADUs up to 900 square feet to be built by right in single-family zoning districts. The historic legislation authorized $5.16 billion in spending over five years along with nearly 50 policy initiatives to counter rising housing costs. The new ADU law is an example of a small policy change that will make a big difference.

Frequently Asked Questions

This FAQ is not legal advice or intended to replace legal advice that cities and towns, or individuals, could and should receive from trusted legal or other professional sources on the development and permitting of ADUs.

EOHLC cannot answer questions about a specific property. Please contact your city or town and speak to a trusted legal, real estate, or building adviser about specific properties.

An ADU must:

• Maintain a separate entrance, either directly from the outside or through an entry hall or corridor shared with the principal dwelling sufficient to meet the requirements of the state building code for safe egress;
• Be either no larger than half the gross floor area of the principal dwelling or 900 square feet, whichever is smaller;
• Meet local municipal restrictions, including, but not limited to, additional size restrictions and/or restrictions or prohibitions on short-term rental if the city or town decides to impose these  

Download the full EOHLC ADU Survey dataset here.

The ADU regulations require Cities and Towns to keep a record of "each ADU permit applied for, approved, denied, and issued a certificate of occupancy, with information about the address, square footage, type (attached, detached, or internal), estimated value of construction, and whether the unit required any variances or a Special Permit". This information is necessary to track Protected ADU creation, assess ADU impacts, and inform future policy changes.

Property owner benefits:

• Provide rental income for property owners, which can help offset maintenance and repair costs
• Offers low-cost housing choice for family to remain in their community (ADU residents cannot be required to be related to the owner)
• Creates more options for older adults to have caregivers live close by or to downsize while remaining in their community

Renter benefits:

• Adds smaller rental units to the housing market to meet the needs of smaller households
• Long-term residents can stay in the neighborhood they love and know

Benefits to Massachusetts:

• Increases much-needed affordable and diverse housing opportunities
• Provides accessible housing to seniors or persons with medical needs or disabilities
• More sustainable and economical use of existing land, structures, and infrastructure than building a single-family home on a new lot
• ADUs are smaller and utilize less water and electricity, making them a more sustainable housing option 

The Affordable Homes Act gave the Executive Office of Housing and Livable Communities (EOHLC) the option to develop regulations. EOHLC created ADU regulations that provide definitions and details about the administration of the ADU provisions in the Zoning Act. The ADU regulation - 760 CMR 71.00: Protected Use Accessory Dwelling Units. The regulations took effect on January 31, 2025 when they were published in the Massachusetts Register by the Secretary of the Commonwealth.

EOHLC, in partnership with the Metropolitan Area Planning Council (MAPC) and Massachusetts Housing Partnership (MHP), has developed Model ADU Zoning to help Cities and towns develop and/or amend local ADU rules. This model includes a Municipal Checklist to help cities and towns evaluate their existing local rules and identify key areas where their rules need to be amended.

Attorney General's Office ADU Decisions

The Attorney General's Office (AGO) Municipal Law Unit (MLU) will publish decisions based on zoning by-law reviews of towns in their Municipal Law Unit Decision Lookup tool. We encourage municipal planners and others working to develop local ADU zoning by-laws to familiarize themselves with this tool and review decisions the AGO will publish related to Accessory Dwelling Units.

State Agencies Guidance

Other state agencies of the Commonwealth of Massachusetts, other than EOHLC, may from time-to-time issue guidance on how other state laws, rules, and regulations relate or impact ADUs. We will cross-post that guidance as they are issued. For property specific questions on Title 5 and septic systems, please contact your local board of health. 

Webinars and Trainings

EOHLC will host educational webinars and trainings to assist cities and towns address any questions they have related to the ADU Law and its regulations, amending existing zoning/by-laws, and adopting local ADU rules.

Property owners with questions about their property should contact their local City or Town planning and/or building departments to learn more about the local rules and permitting processes that relate to their specific property. EOHLC cannot answer individual questions about specific properties.

Grants to Assist Creating Local ADU Rules

Municipalities who need assistance drafting, conducting community planning, and enacting local ADU rules may apply for funding through the Community One Stop for Growth. Grants in the One Stop, such as Community Planning Grant Program and Housing Choice Grant Program that are part of the Planning and Zoning One Stop Development Continuum may fund efforts related to local ADU rules adoption.

External Resources:

• The ABCs of ADUs (AARP)
• Webinar: Accessory Dwelling Units (AARP)
• Accessory Dwelling Units Knowledgebase Collection (American Planning Association)