Massachusetts ADU FAQ for Homeowners
Answers to common questions about accessory dwelling units under the Massachusetts ADU law, G.L. c. 40A, § 3, and its regulations, 760 CMR 71.00. For help with a specific property, see our Massachusetts ADU lawyer page or our ADU homeowner checklist.
When did the Massachusetts ADU law take effect?
The ADU provisions of the Affordable Homes Act (St. 2024, c. 150, § 8) took effect on February 2, 2025. The Executive Office of Housing and Livable Communities issued final regulations, 760 CMR 71.00, the same season.
What is a protected-use ADU?
It is a self-contained housing unit with its own living, sleeping, cooking and sanitary facilities, on the same lot as a principal dwelling, that meets the size limit in the Zoning Act. Only one ADU per lot can qualify as a protected-use ADU. It can be inside, attached to, or detached from the principal dwelling.
Does the law apply in my city or town?
It applies in every Massachusetts city and town except Boston, in any zoning district where single-family homes are allowed, including overlay districts where the underlying zoning allows single-family homes.
Can I add an ADU if my house is a two-family or multi-family home?
Yes. According to state guidance, a protected-use ADU must be allowed on a lot with a principal dwelling in any district that allows single-family homes, even if the principal dwelling is a two-family or multi-family building. Only one protected-use ADU is allowed per lot.
How is the 900-square-foot limit calculated?
The ADU may not exceed one-half of the gross floor area of the principal dwelling or 900 square feet, whichever is smaller. A 1,400-square-foot house can support a 700-square-foot ADU. Under state guidance, basements that meet building-code ceiling heights count toward gross floor area, while crawl spaces, garages, attics and enclosed porches generally do not. If a lot has more than one principal dwelling, the largest one is used.
Can my town require me to live on the property?
No. A city or town cannot require that either the ADU or the principal dwelling be owner-occupied for a protected-use ADU.
How much parking can my town require?
No more than one additional space. If any part of the lot is within one-half mile of a subway station, commuter rail station, ferry terminal or bus station, no additional space can be required. In its 2025 review of one town’s bylaw, the Attorney General’s Office treated a regular regional bus stop as a bus station for this purpose.
Can I rent the ADU to anyone?
Generally yes, for long-term rentals. A city or town cannot limit occupants by income, age or family relationship, and cannot unreasonably restrict long-term rentals. It may restrict or ban short-term rentals of 31 consecutive days or less.
What can my town still require?
A building permit, building and fire code compliance, Title 5 septic compliance, reasonable dimensional limits no stricter than those for the principal dwelling, single-family homes or accessory structures, clear and objective site plan review, reasonable fees, and reasonable rules in historic districts and certain overlay districts.
My HOA or condominium documents prohibit ADUs. Does the state law override them?
No. State guidance says the ADU law does not address homeowners’ associations, and it does not amend the condominium statute, G.L. c. 183A. Private restrictions in deeds, covenants, HOA rules or condominium documents should be reviewed before you plan an ADU.
Can I sell the ADU separately from the main house?
Not as a matter of zoning. Selling an ADU separately would generally require converting the property to a condominium under G.L. c. 183A and meeting all related requirements. Talk to counsel before taking any steps toward a separate sale.
My local bylaw still has old ADU rules. Which rules apply?
Local zoning provisions inconsistent with the state ADU law have been unenforceable since February 2, 2025, whether or not the bylaw has been amended. If a local official applies a conflicting rule, the decision can generally be appealed.
How do I appeal an ADU permit denial?
Appeal paths depend on who made the decision. A decision by a building commissioner can generally be appealed to the zoning board of appeals, and the board’s decision can then be appealed to the Land Court or Superior Court. The filing deadlines are short, often 20 or 30 days. Contact an attorney as soon as you receive a denial.
Do I need a lawyer to build an ADU?
Not always. Many projects move through permitting without a lawyer. Legal help is most useful when your lot or house is nonconforming, when a private restriction or HOA is involved, when a permit is denied or conditioned, when family members are sharing costs, or when you plan to rent the unit.
Official Sources
- G.L. c. 40A, § 3 and § 1A (definition of accessory dwelling unit)
- 760 CMR 71.00, Protected Use Accessory Dwelling Units
- The Commonwealth’s state ADU FAQ
- Your city or town zoning bylaw or ordinance and building department
Planning an ADU or facing a permit problem? Contact Muggeo & Associates or call (978) 741-1177. Our Salem office serves homeowners across the North Shore and Massachusetts.
This page is general information, not legal advice. ADU rules depend on your city or town, your lot, and the structure involved, and local bylaws and state guidance continue to change. Contacting the firm does not create an attorney-client relationship. Prior results do not guarantee future outcomes. Last reviewed November 2026.