Accessory Dwelling Units (ADUs) in Massachusetts

The Affordable Homes Act, signed in August 2024, made accessory dwelling units a protected use under Section 3 of the Zoning Act. The change took effect on February 2, 2025, and the state’s Executive Office of Housing and Livable Communities (EOHLC) adopted regulations to implement it.

What’s protected

In general, one ADU per lot is allowed by right in single-family residential zoning districts, without a special permit. A protected ADU:

• is a self-contained unit with its own living, sleeping, cooking, and sanitary facilities;
• can be inside, attached to, or detached from the principal dwelling;
• is limited to 900 square feet or half the gross floor area of the principal dwelling, whichever is smaller.

Communities cannot require that the owner live on the property, and parking requirements are limited. Generally, no parking can be required for an ADU near transit, and no more than one space elsewhere.

What communities can still regulate

Cities and towns can apply reasonable regulations, including site plan review and dimensional rules such as setbacks and height, as long as they aren’t more restrictive than what applies to a single-family home. Communities can also restrict short-term rentals. A second ADU, or an ADU outside these limits, may still be allowed under local rules, often by special permit.

What to check first

• Your local bylaw. Many communities have amended their ADU rules, and some older provisions may no longer be enforceable.
• Site constraints. Septic capacity, wetlands, and setbacks still apply and often decide what fits.
• Building and health codes. ADUs are full dwelling units and are permitted that way.

General information, not legal advice. State regulations and local bylaws continue to evolve.