What is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit located on the same lot as a primary residence. ADUs can be attached (like a basement or garage apartment) or detached (like a backyard cottage). They typically have their own entrance, kitchen, bathroom, and living space, and are often used for rental income, multigenerational housing, or guest accommodations.

How big can I build my ADU?

Municipalities must allow construction of ADU’s up to a minimum of 900 sq feet but may allow larger.

Can an ADU be rented out?

Yes an ADU can be rented to anyone, it is not required to be owner occupied or occupied by family but that is an option. A town may however, restrict short term rentals (Airbnb etc.).

What was the big change in Massachusetts law regarding ADU’s?

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.

Does the recent law change impact my town?

All towns and cities in Massachusetts besides Boston are now subject to the new rules and regulations governing ADU’s.

What does this mean?

There are now much fewer restrictions preventing the construction of ADU’s. This will help increase the speed of the approval process during the application process and review of building/site plans for ADU’s.

Can a municipality block construction of an ADU on a lot with a multifamily building on it?

No, a municipality cannot limit Protected Use ADUs to lots with only single-family homes on them. See the decision East Bridgewater Accessory Dwelling Unit AGO Decision - April 14, 2025.

Do I need to provide additional parking for an ADU?

If the ADU is located within half a mile of a train station or bus stop parking is not required. If it is further than half a mile a municipality may require up to 1 parking spot.