Massachusetts Accessory Dwelling Unit (ADU) Lawyer

Massachusetts homeowners can now add an accessory dwelling unit, often called an ADU, in-law apartment or backyard cottage, without a special permit in most of the Commonwealth. The Affordable Homes Act changed the Zoning Act, and since February 2, 2025 cities and towns must allow one “protected-use” ADU per lot as of right wherever single-family homes are allowed. Muggeo & Associates helps homeowners in Salem and across the North Shore plan ADUs, get through local permitting, challenge local rules that conflict with state law, and rent their units with confidence.

Massachusetts ADU Law at a Glance

The state ADU law is in G.L. c. 40A, § 3 (with the definition in § 1A), added by St. 2024, c. 150, § 8, and the Executive Office of Housing and Livable Communities regulations at 760 CMR 71.00. For a protected-use ADU:

As of right: One ADU per lot is allowed without a special permit, variance or other discretionary zoning approval in any district that allows single-family homes. This applies whether the principal dwelling is a single-family, two-family or multi-family home.
Size: The ADU may be up to one-half of the principal dwelling’s gross floor area or 900 square feet, whichever is smaller. Basements that meet building-code ceiling heights count toward gross floor area.
Attached or detached: The unit can be inside the house, attached to it, or in a separate building such as a converted garage or new cottage. A town cannot require one form over the other.
No owner-occupancy requirement: A city or town cannot require that the owner live in either the ADU or the main house.
Parking: A town cannot require more than one additional parking space, and cannot require any additional space if any part of the lot is within one-half mile of a subway, commuter rail, ferry or bus station.
No occupancy restrictions: A town cannot limit who lives in the ADU based on income, age or family relationship.
No minimum lot size or density limits: Protected-use ADUs cannot be subject to a minimum lot size and are not counted in density calculations.
Boston: The City of Boston is not covered by these Zoning Act provisions and has its own zoning code.

What Your City or Town Can Still Regulate

The law does not eliminate local review. A city or town may apply reasonable rules, as long as they do not make ADUs unreasonably costly or infeasible. Local rules that apply include:

A building permit and compliance with the State Building Code, Fire Code and health codes.
Setbacks, height, lot coverage and similar dimensional limits, but no stricter than the most permissive standard that applies to the principal dwelling, a single-family home or an accessory structure in that district.
Site plan review, if it uses clear and objective standards.
Title 5 septic requirements, including upgrades where the existing system lacks capacity.
Short-term rental restrictions or bans for rentals of 31 days or less.
Reasonable design standards in historic districts and certain floodplain or aquifer overlay districts.
A special permit for a second or additional ADU on the same lot.

When Local Rules Conflict With State Law

Under the state law, local zoning provisions that conflict with it have been unenforceable since February 2, 2025, even if the local bylaw or ordinance has not been updated. Many towns have rewritten their ADU rules, and not every new rule complies.

For example, in an October 24, 2025 decision on Nahant’s ADU bylaw, the Attorney General’s Office struck provisions that limited ADUs to single-family lots, excluded basements from the floor-area calculation, imposed stricter setbacks and a lower height cap than allowed for single-family homes, restricted long-term rentals, and required a parking space even near a bus stop served by regional transit. The Attorney General reviews town bylaws, but not city ordinances, so city residents may need to raise conflicts directly in the permitting process or on appeal.

Some older local ordinances also contain ADU rules adopted before 2025. Salem’s ADU web page, for instance, still describes a rent limit tied to federal fair market rent. Whether a pre-2025 local requirement can be applied to a protected-use ADU is a question to resolve before you design and build.

How We Help Homeowners

Feasibility and zoning review of your lot, the principal dwelling and your local bylaw or ordinance before you invest in plans.
Permit applications and communications with building commissioners, planning boards and zoning officials.
Appeals of permit denials, conditions or enforcement orders to the zoning board of appeals and the courts, including the Land Court and Superior Court.
Title, deed restriction, HOA and condominium review, since the state ADU law does not override private restrictions or condominium documents.
Contractor agreements, including review under the Massachusetts Home Improvement Contractor law, and disputes over defective or unfinished work.
Family arrangements for in-law units, including agreements among family members who contribute to construction costs.
Leases and landlord compliance if you will rent the ADU.
Neighbor disputes and challenges to an issued permit.

Renting Out Your ADU

An ADU rented to a tenant is a residential rental, and Massachusetts landlord-tenant law applies in full. Owners should understand the Massachusetts security deposit law, the state lead paint law for homes built before 1978, the State Sanitary Code, and local short-term rental rules. A clear written lease and proper move-in paperwork prevent most disputes.

ADU Resources

Massachusetts ADU FAQ for Homeowners
Building an ADU in Massachusetts: Homeowner Checklist
The Commonwealth’s state ADU FAQ and ADU information page

Serving Salem and the North Shore

We help homeowners with ADU questions in Salem, Peabody, Beverly, Marblehead, Swampscott, Danvers, Lynn and communities throughout Essex County and Massachusetts. See all areas we serve and our real estate and landlord-tenant practice.

Frequently Asked Questions

Do I need a special permit to build an ADU in Massachusetts?

Generally no. Since February 2, 2025, one protected-use ADU per lot is allowed as of right in any zoning district that allows single-family homes. Cities and towns can require a building permit and reasonable, clear and objective site plan review, but cannot require a special permit or variance for a qualifying protected-use ADU. A special permit can be required for a second or additional ADU on the same lot.

How large can a protected-use ADU be?

Up to one-half of the gross floor area of the principal dwelling or 900 square feet, whichever is smaller. A city or town may allow larger units but cannot set the limit below 900 square feet.

Do I have to live on the property?

No. State regulations prohibit cities and towns from requiring that either the ADU or the principal dwelling be owner-occupied for a protected-use ADU.

Can my town ban short-term rentals of an ADU?

Yes. A city or town may restrict or prohibit short-term rentals of an ADU, meaning rentals of 31 consecutive days or less under G.L. c. 64G. It cannot unreasonably restrict long-term rentals.

What if my building permit or zoning approval for an ADU is denied?

Local zoning rules that conflict with the state ADU law are unenforceable. A denial can generally be appealed locally to the zoning board of appeals and then to court, and the deadlines are short. Speak with an attorney promptly after any denial.

Planning an ADU or facing a permit problem? Contact Muggeo & Associates or call (978) 741-1177. Our Salem office serves homeowners across the North Shore and Massachusetts.

This page is general information, not legal advice. ADU rules depend on your city or town, your lot, and the structure involved, and local bylaws and state guidance continue to change. Contacting the firm does not create an attorney-client relationship. Prior results do not guarantee future outcomes. Last reviewed November 2026.