Buying a home with an ADU in Massachusetts

Massachusetts state-level rules buyers should know

• • Chapter 358 of the Acts of 2024 (effective Feb 2025) legalized ADUs statewide. Cities cannot ban them outright.
• • ADUs allowed by-right in single-family zones, up to 900 sq ft or 50% of primary residence.
• • No owner-occupancy required statewide — but local short-term-rental rules apply.
• • Cities can still require design review on detached units in historic districts.
• • Pre-2025 'in-law suites' often lack separate ADU permits — verify the legal category before assuming rental rights.

What to check when buying

• ✓ Verify whether the unit is a legal ADU or just an in-law suite under older local zoning — these have different rental rights.
• ✓ Pull the building permit through the local building inspector's office. State permit consolidation is in progress but uneven.
• ✓ For Boston, check the city's accessory-apartment registry.
• ✓ If the unit is in a historic district, confirm Massachusetts Historical Commission has signed off.
• ✓ Verify the egress and ceiling height meet IRC standards — older converted basements often fall short.

Permit info for Massachusetts cities

The strongest signal of a legitimate ADU is a clean permit history at the city. Use these jurisdictional guides to cross-check what the seller's disclosure tells you.

• Permits in Boston

Related

• Full ADU buying guide
• ADU value analysis
• Verified ADU builders in Massachusetts
• Boston permit overview
• ADU cost guide