Massachusetts Accessory dwellings (2025): what it allows on a lot
Accessory dwellings (2025) is Massachusetts law, and the official source is at mass.gov.
Cities and towns must allow one accessory dwelling up to 900 square feet by right on lots with a single family home. Towns may not require owner occupancy or a special permit for the first accessory dwelling (Chapter 150 of the Acts of 2024, in force February 2, 2025); Boston has its own ordinance.
Whether it applies to one lot turns on where the lot is and what it is zoned; the city, county or state office named in the law decides. Mapped areas are approximate. This is a plain reading of public law with its source, not legal advice.
Free, no account. ParcelSheet shows the lot's mapped size, parcel lines and flood zone, and this law on the lot's Massachusetts sheet.
Other Massachusetts laws on a lot: Title 5 septic inspection.