Massachusetts’ ADU law protects a defined “Protected Use ADU” pathway, but it does not erase every local requirement. Under the statutory definition, a Protected Use ADU may be no larger than one-half the gross floor area of the principal dwelling or 900 square feet, whichever is smaller. For example, if the principal dwelling is 1,600 square feet, the half-area limit is 800 square feet. For a Protected Use ADU, the by-right district test is a district where a single-family home may be built by right or by special permit; the principal dwelling on the lot does not itself have to be single-family. The state framework limits the Protected Use to one ADU per lot and retains reasonable local requirements. This is not a blanket right to build any ADU up to 900 square feet on any lot.
Effective February 2, 2025, municipalities cannot require owner occupancy or a family relationship for the ADU or principal dwelling, or require discretionary zoning approval for the use or rental of a Protected Use ADU within the statutory boundary. Check the statute and current state guidance to determine whether a proposed unit fits this protected pathway.
Local requirements still matter. The state identifies reasonable controls such as site-plan review, Title 5, dimensional setbacks, building bulk and height, alongside applicable building, health, and safety requirements. Municipalities may also restrict or prohibit short-term rentals. The current state FAQ ties the short-term-rental boundary to stays subject to the Room Occupancy Excise, which covers stays of not more than 31 consecutive calendar days, and notes statutory exemptions such as seasonal-employee lodging and tenancies at will or month-to-month leases. Do not apply that duration to every rental classification without checking the statute.
Confirm protected-use status and local rules
Identify the municipality, zoning district, project, and intended rental term. Check whether the proposed unit meets the current statutory and regulatory definition of a Protected Use ADU, then confirm local requirements for site review, septic or Title 5, dimensional standards, and short-term rentals. An ordinary rental and a short-term stay are different uses; state protection against certain zoning barriers does not itself provide a short-term-rental license or approve building, fire, sanitary, or occupancy conditions.
The Executive Office of Housing and Livable Communities updated its FAQ on September 17, 2026. Its ADU page also reports proposed revisions to regulation 760 CMR 71.00, with public comments scheduled through October 9, 2026. Those proposals are not yet operative merely because they are published for comment. Recheck the official page, current regulation, municipality’s rules, and any relevant Attorney General decision before relying on a specific result. State guidance cannot decide an individual property’s eligibility.