Accessory Dwelling Unit (ADU) Rules in Massachusetts
A secondary living unit on the same lot as a primary home, such as a garage conversion, basement apartment or detached backyard cottage.
What the state law requires
Accessory dwelling units up to 900 square feet are allowed by right in single-family zoning districts in every municipality. Special permits, variances and discretionary hearings are prohibited for qualifying units.
Citation: Mass. Affordable Homes Act § 8 (Ch. 150, Acts of 2024) · https://malegislature.gov/ · Retrieved 2026-08-29
State law usually sets the floor for what local governments must allow. Your city or county can still apply objective standards, so confirm the local rules as well.
Get a checklist for your address
Questions to ask your local department
- Ask the local planning or building department whether a state ADU statute applies to your parcel and whether the city has a conforming local ordinance.
- Request the objective standards used for ministerial review: size cap, height, setbacks and lot coverage.
- Confirm utility connection requirements and any separate metering rules.
- Ask whether owner occupancy, short-term rental use, or parking is regulated for your unit type.
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Accessory Dwelling Unit (ADU) in Massachusetts: common questions
Does Massachusetts have a statewide accessory dwelling unit (adu) law?
Accessory dwelling units up to 900 square feet are allowed by right in single-family zoning districts in every municipality. Special permits, variances and discretionary hearings are prohibited for qualifying units.
Does the state law replace my city or county rules?
Usually it sets a floor, not a ceiling. A statewide statute typically tells local governments what they must allow, while your city or county can still apply objective standards such as setbacks, height and utility connections. Local rules cannot usually contradict the state mandate, but they can add reasonable requirements.
What should I confirm locally before I start?
Ask the local planning or building department whether a state ADU statute applies to your parcel and whether the city has a conforming local ordinance. Request the objective standards used for ministerial review: size cap, height, setbacks and lot coverage. Confirm utility connection requirements and any separate metering rules. Ask whether owner occupancy, short-term rental use, or parking is regulated for your unit type.
ZoneFig provides general reference information, not legal advice. Yard and zoning rules are adopted locally, so the only binding answer for your address comes from your city, town or county planning and building department. Typical thresholds shown here describe patterns across many jurisdictions and are not the rule at any specific property.