Massachusetts Tiny Home & ADU Zoning Laws
Massachusetts just went through one of the most significant statewide zoning shifts covered in this entire series — but there's a major exception that trips up a lot of people researching this topic.
- The Affordable Homes Act requires every city/town to allow one ADU by-right on single-family lots, effective February 2025.
- Boston is explicitly exempt — it operates under separate zoning authority with its own different ADU program.
- Max ADU size: 900 sq ft or 50% of the primary home's floor area, whichever is smaller.
- Cape Cod (Barnstable County) restricts short-term rentals of ADU-classified units specifically.
- Local bylaws that conflict with the state law are unenforceable, even if not formally repealed yet.
The exception almost everyone misses: the Affordable Homes Act, signed by Governor Maura Healey in August 2024 and fully effective by February 2025, requires every Massachusetts city and town to allow at least one ADU by-right on single-family lots, with no special permit needed if state requirements are met.5,7 Boston is explicitly exempt. Boston operates under its own separate zoning authority and is not subject to M.G.L. c. 40A, the statute the Affordable Homes Act amended — Boston has its own, different ADU program entirely.1 If you're researching Boston specifically, none of the statewide by-right provisions described below apply there.
1. What the Statewide Law Actually Requires
The statewide ADU mandate is codified as 760 CMR 71.00, adopted under the authority of M.G.L. c. 40A, § 3 (the "Dover Amendment") as amended by St. 2024, c. 150, § 8, and took effect February 2, 2025.6,9
| Requirement | Detail |
|---|---|
| Maximum size | 900 sq ft or 50% of the primary dwelling's gross floor area, whichever is smaller1,6 |
| Units per lot | One ADU by right per single-family lot1 |
| Permitting | No special permit or zoning board approval required if state criteria are met — still need a building permit, septic/sewer compliance, and Certificate of Occupancy6 |
| Construction standard | Full residential building code compliance: permanent foundation, code-compliant plumbing, electrical, HVAC, insulation, and egress1 |
If a town's existing bylaws conflict with these provisions, those bylaws are unenforceable under current law, whether or not the town has formally repealed them.1 Many municipalities were still updating their local bylaws and permitting procedures as of 2026.3
2. A Notable Short-Term Rental Restriction: Cape Cod
Barnstable County, covering Cape Cod, treats tiny homes supportively as ADUs, but with a specific condition worth knowing if short-term rental income is part of your plan: ADU rules there require owner-occupancy of the primary home or the ADU for more than six months annually, and explicitly restrict platforms like Airbnb.4 This tracks the state regulation itself, which specifically permits municipalities to restrict short-term rentals of protected ADUs under M.G.L. c. 64G, separate from the owner-occupancy protections that apply to the ADU generally.9 Long-term leasing remains a viable option, but this specifically closes off the short-term rental route for ADU-classified units in this area. See our STR feasibility guide for other zoning traps like this one.
3. County and Town Examples
| County / Town | Notable Detail |
|---|---|
| Berkshire County | Follows Appendix Q; tiny homes up to 400 sq ft, 6 ft 8 in minimum ceiling height2 |
| Middlesex County | ADUs allowed, but the primary home must be owner-occupied and both units must belong to the same person3 |
| Greenfield | Tiny houses approved under a specific City Council ordinance; must be owner-occupied, not rented to a tenant3 |
| Cheshire | Permanent mobile home living allowed in some districts, but full-time RV living is not approved in R-1 districts specifically3 |
Research record: The Boston exemption is a claim easy to get wrong or leave vague, so we verified it directly against the state's own implementing regulation, 760 CMR 71.00 (published January 31, 2025, effective February 2, 2025), and a Massachusetts real estate licensee continuing-education course document from the Executive Office of Housing and Livable Communities, rather than relying on secondary summaries alone. We also confirmed the Cape Cod short-term rental restriction traces to a specific provision within that same regulation (permitting municipal STR restrictions under M.G.L. c. 64G) rather than being a purely local Barnstable County policy invented independently of state law. Information last checked August 2026.
How to Verify Your Specific Situation
- Confirm immediately whether your target property is inside or outside Boston city limits, since the entire statewide framework doesn't apply within the city.
- If planning short-term rental income specifically, check whether your target town restricts Airbnb-style use on ADUs the way Barnstable County does.
- Confirm your specific municipality has updated its local bylaws to comply with the Affordable Homes Act, since implementation was still rolling out as of 2026.
- Confirm septic or sewer compliance requirements, since these remain required even under the by-right permitting framework.
Considering the ADU route? See how it compares nationally.
Read the National ADU Placement GuideSources
- Autonomous, "ADU Massachusetts Guide: 2026 Laws, Costs & How to Build."
- Zook Cabins, "Tiny Home Regulations In Massachusetts (2026 Guide)."
- TinyHouse.com, "Massachusetts Tiny Home Rules and Regulations."
- Great Lakes Tiny Home, "What Counties in Massachusetts Allow Tiny Houses."
- Percy Law Group, "Accessory Dwelling Units in Massachusetts: The Essential 2026 Legal Guide."
- BuildX, "Do Massachusetts Homeowners Have The Right By Law To Build An ADU in 2026?"
- Massachusetts Executive Office of Housing and Livable Communities, press release, February 3, 2025.
- Mass.gov, "760 CMR 71.00: Protected Use Accessory Dwelling Units" official implementing regulation.
- Mass.gov, 760 CMR 71.00 regulatory authority citation (M.G.L. c. 40A, § 3; St. 2024, c. 150, § 8) and short-term rental provision (M.G.L. c. 64G).
