What is an ADU?
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 policy recently signed by the governor allows property owners to build an ADU without having to get special or discretionary approval from the local zoning board.
ADUs can be internal within an existing primary residence, like converting a basement into an apartment, attached to a primary residence as a new construction addition, or completely detached, like a cottage or converted detached garage in a backyard.
What is the law?
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 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 law on ADUs is an example of a small policy change that will make a big difference.
Massachusetts is a leader in finding innovative solutions to our biggest challenges. Rising housing costs and homelessness are not unique challenges for our state, but we can lead the way in solving them.
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
| Municipalities may impose reasonable restrictions and requirements for: | Municipalities cannot: |
|---|---|
|
|
|
|
|
|
|
|
What are the benefits of ADUs?
Property owner benefits:
- Provide rental income for property owners, which can help offset maintenance and repair costs
- Offers low-cost housing opportunity for adult children and other relatives to remain in their community (although occupants of the ADU do not have to be related to the property owner)
- Enables more options for older adults – either as an opportunity for caregivers to live close by or to downsize while remaining in their community
Renter benefits:
- Adds smaller rental units to the housing inventory to meet the needs of smaller households
- Long-term residents can stay in the neighborhood they love and know (work in)
Benefits to Massachusetts:
- Increases much-needed affordable and diverse housing opportunities
- Provides accessible housing to seniors or persons with medical needs or disabilities and their care givers
- Compact growth makes use of our existing land use, structures and infrastructure, which can be more sustainable and far more economical 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
ADU Regulations
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.
Model ADU Zoning
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.
Technical Assistance for Municipalities
Municipal TA Office Hours
EOHLC will offer office hours for municipal planners and building inspectors to ask questions about the regulations and implementation of the ADU Law and to help any community go through questions about implementing local ADU rules. We will reach out to all municipalities and regional planning agencies with dates and registration for these office hours.
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.
| Webinar | Recording | Slides |
|---|---|---|
| ADU Model Zoning Webinar - EOHLC, in partnership with MAPC and MHP will share information about the ADU Model Zoning and discuss how Cities and Towns can use this tool. | YouTube Recording by MAPC | ADU Model Zoning Webinar Slide Deck |
| CPTC session offered by EOHLC staff during the 2025 Annual Conference. | N/A | ADU CPTC Presentation |
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.
Resources
Frequently Asked Questions
While we are providing this FAQ, it is not legal advice or intended to replace legal advice that cities and towns, or individuals, could receive from trusted legal or other professional sources on the development and permitting of ADUs. We will update this FAQ from time to time as new questions are asked frequently.
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.
| Agency | Guidance | Published | Related Resources |
|---|---|---|---|
| Massachusetts Department of Environmental Protection | Guidance on Title 5 (310 CMR 15.000) Compliance for Accessory Dwelling Units | April 7, 2025 | Title 5/Septic Systems Policies & Guidance |
| MassGIS (Bureau of Geographic Information) | MassGIS Addressing Guidance for Accessory Dwelling Units (ADUs) | March 10, 2025 | Address Standard for Massachusetts Municipalities |