ADUs in Massachusetts
An ADU is a small, self-contained home on the same lot as a main house. Think in-law suite, backyard cottage, or garage apartment, with its own kitchen, bath, and entrance. And here is the big news: since February 2025, Massachusetts law lets you build one by right on almost every single-family lot in the state.
The new state law, in plain English
What the law guarantees
- One ADU per lot, by right, in any single-family residential zoning district
- Up to 900 square feet, or half the size of the main house, whichever is smaller
- Attached, detached, or internal conversions all qualify
- Towns cannot require you to live in either unit, and cannot demand a family relationship
- Towns cannot require more than one extra parking space, and none at all near transit
- ADUs do not count against density limits
What towns can still regulate
- Setbacks, height, and lot coverage rules
- Site plan review (non-discretionary)
- Title V septic requirements
- Short-term rental restrictions, many towns ban Airbnb-style rentals in ADUs
- Special permits for a second ADU or for larger units
Important: Boston is exempt from the state law and runs its own ADU program with different rules.
Official resources
Start with the state's own pages. These are the authoritative sources, and I keep this page synced with them.
- Massachusetts ADU homepage and guide (mass.gov)
- Official ADU FAQs from the Executive Office of Housing and Livable Communities
- ADU Design Challenge Showcase, free downloadable winning home plans
- ADU application tracker, see approvals happening across the state
- MyMassADU.org, the state resource center: enter an address to check feasibility and financing
- MassHousing ADU Loan Program, up to $250,000 for detached ADUs
- MHP ADU Incentive Program, professional feasibility studies capped at $500
- Boston's ADU program (separate rules from the state law)
How it works, step by step
- Confirm your lot qualifies. Check that your property sits in a single-family residential zoning district, then review your town's ADU bylaw for setbacks, height, parking, and rental rules. When in doubt, call the town building department.
- Get a feasibility study. The state's incentive program offers professional feasibility studies for no more than $500, covering site conditions, zoning, utilities, and cost estimates.
- Design the unit. Hire an architect, work with a design-build firm, or start from the state's free Design Challenge plans. Decide: convert existing space, build an addition, or go detached.
- Line up financing. MassHousing's ADU loan goes up to $250,000 for detached units. A HELOC or renovation loan works too. MassHousing requires plans and permits in hand before you apply.
- Pull the building permit. By-right means no zoning hearing. File a building permit with a site plan, floor plans, and elevations. Typical permitting runs 90 to 120 days.
- Build. Construction usually takes 4 to 8 months. Realistic total timeline from first study to move-in: 8 to 14 months.
- Close out. Certificate of occupancy, town registration, updated homeowner's insurance, and if you are renting, comply with the sanitary code and any local rental registration.
What it costs
- Basement, attic, or garage conversion: roughly $150,000 to $275,000
- Attached addition: roughly $200,000 to $350,000
- Detached new build: roughly $275,000 to $450,000 and up
- Rule of thumb around Greater Boston: $250 to $400 per square foot
- Soft costs (design, survey, engineering, permits): $10,000 to $30,000
Town-by-town: where I work
The state law sets the floor everywhere, but each town writes its own details. Here is where things stand across my service areas. Towns marked updated have rewritten their bylaws to match the state law. Where local text is outdated, the state's by-right rule governs regardless.
Cape Ann
- Gloucester: Local text predates the law, state by-right rule applies. Up to 900 sq ft or 50%.
- Rockport: Updated September 2025. By-right, no short-term rentals.
- Essex: Updated December 2025. By-right, no short-term rentals.
- Manchester-by-the-Sea: Updated March 2025. Unique two-tier system, including "Large" ADUs up to 2,000 sq ft.
- Ipswich: Conforming amendment proposed summer 2026, watch for the town vote.
North Shore
- Beverly: Amendments drafted, building inspector applying state language.
- Salem: Updated May 2025. By-right, owner-occupancy removed, no short-term rentals.
- Peabody: Local text outdated, state by-right rule applies.
- Danvers: Local text outdated, building inspector applying state interpretation.
- Lynn: Updated December 2025. By-right, detached allowed.
- Swampscott: Local text predates the law, state by-right rule applies.
- Marblehead: Updated May 2025. By-right, max 2 bedrooms, no short-term rentals.
- Saugus: Local text outdated, building inspector applying state law.
Greater Boston
- Boston: Exempt from the state law. Owner-occupants can build an internal ADU by right; attached or detached units generally need zoning relief. Boston runs its own ADU guidebook, workshops, and loan programs.
- Revere: Updated 2025. By-right, no short-term rentals, flood-zone rules apply.
- Chelsea: Updated April 2026. By-right in single-family districts.
- Everett: State by-right law applies, confirm details with the city.
- Winthrop: Draft ordinance in progress.
- Medford: Update in committee, state by-right rule applies meanwhile.
Merrimack Valley
- Newburyport: By-right via written zoning determination. No short-term rentals once an ADU is established.
- Wakefield: State by-right law applies, confirm details with the town.
Rules change as towns vote. Before you buy or build for an ADU, I verify the current bylaw with the town directly.
Designs and floor plans
You do not have to start from a blank page. Massachusetts now has a deep bench of ADU design resources.
- Free state plans: The ADU Design Challenge Showcase publishes winning designs free, from compact 450 sq ft studios to full 900 sq ft cottages, drawn by Massachusetts architects.
- Address lookup: MyMassADU.org lets you enter a property address to visualize an ADU on the lot and explore financing.
- Boston guidebook: The city's ADU guidebook includes pre-designed schemes for Boston properties.
- Design-build firms: Firms like BuildX (Carver/Hanover, 14 published models with pricing), Backyard ADUs (35+ Massachusetts projects), Any Season Design Build (Salem), Annex North Design (Burlington, custom ADU drafting), and Clarke Building Company (North Shore) specialize in ADUs.
- Feasibility first: The MHP incentive program connects you with professionals who will study your lot for $500 or less.
The opportunity
For homeowners
An ADU can house family, create rental income, or both. Because towns cannot require owner-occupancy, you have flexibility in how you use the property. Many of my clients are looking at ADUs as a way to help adult children or aging parents live close, while adding long-term value to the property.
For buyers and investors
ADU-eligible lots are drawing stronger buyer interest, and a permitted ADU adds real functionality and income potential to a property. Underwrite carefully: most towns restrict short-term rentals in ADUs, so plan on 30-day-plus tenancies. And expect the assessment, and the tax bill, to reflect the improvement. I evaluate ADU plays the way I evaluate any investment: real numbers, honest risks, no hype.
ADU news timeline
- August 2024: Governor Healey signs the Affordable Homes Act, including the ADU provisions.
- January 2025: State ADU regulations (760 CMR 71.00) take effect.
- February 2025: By-right ADU rights take effect statewide.
- Spring 2025: Manchester-by-the-Sea, Marblehead, and Salem update local bylaws; towns across the state follow.
- December 2025: Governor launches ADU acceleration campaign: design challenge, $10M in technical assistance, new financing.
- March 2026: MassHousing ADU Loan Program opens applications.
- May 2026: ADU Design Challenge winners announced, plans made free to the public.
- 2026: Over 2,000 ADUs approved statewide since the law took effect, with 70% of Massachusetts communities approving at least one.
Talk ADUs with Jarvid
Build one, buy for one, or invest in one. Get the town rules verified and the numbers done right.