One page of orientation before anything else: what an ADU is, how the rules work, and the order to do things in.
An Accessory Dwelling Unit is a smaller independent dwelling located on the same lot as a principal residence. Under Massachusetts law, it is a self-contained unit with its own sleeping, cooking, and sanitary facilities and a separate entrance, no larger than half the gross floor area of the principal dwelling or 900 square feet, whichever is smaller. Source: Chapter 150 of the Acts of 2024, Sections 7 and 8, via mass.gov.
Massachusetts allows one qualifying ADU by right in single-family zoning districts statewide, effective February 2, 2025, implemented through 760 CMR 71.00. By right does not mean no permits: building codes, dimensional rules, septic and utility capacity, wetlands, flood zones, historic districts, and private restrictions all still shape what a specific lot can support.
Educational information only. This resource provides general education and is not legal, tax, appraisal, engineering, lending, zoning, or construction advice. Verify all requirements with the applicable municipality and qualified professionals.