02/26/2026
Massachusetts ADU Law – What Changed (2025)
Under the Affordable Homes Act signed by Maura Healey and the Healey-Driscoll Administration, Accessory Dwelling Units (ADUs) are now allowed by-right statewide.
This means cities and towns cannot require a special permit or variance for an ADU in a single-family zoning district.
The law took effect February 2, 2025.
What is now allowed
An ADU is a small, independent housing unit located on the same lot as a single-family home.
It may be:
• Inside the home (basement, attic, or interior conversion)
• Attached to the house (addition)
• A detached structure (backyard cottage / small outbuilding)
• A converted garage
All of the above are allowed by right.
Size limit
An ADU must be:
• No larger than 900 square feet
(Your text confirms: “ADUs less than 900 square feet can be built by-right statewide.”)
Zoning approval is no longer required
Towns and cities:
• ❌ Cannot deny an ADU through zoning
• ❌ Cannot require a special permit
• ❌ Cannot require a variance
Only normal permitting still applies (building permit, septic/Title 5, etc.).
What still applies (important for your projects)
Even though zoning approval is eliminated, the project still must comply with:
• Building Code
• Fire / eLife safety
• Health and septic (Title 5)
• Local dimensional rules that are not more restrictive than the primary dwelling
• Any applicable conservation / environmental regulations
Why the state passed this law
According to the Administration, the goal is to:
• create housing for seniors,
• allow independent living for adults with disabilities,
• create smaller and more affordable housing options,
• allow homeowners to generate rental income.
The law was promoted by:
• Kim Driscoll
• Ed Augustus
• and implemented through the
Executive Office of Housing and Livable Communities
How many ADUs the state expects
The state estimates 8,000 to 10,000 new ADUs over the next five years statewide.
Very important clarification for our clients
Even though ADUs are now legal by-right:
This does not eliminate:
• conservation review,
• wetlands / buffer zone review,
• septic upgrades,
• or other environmental permitting.
For you as a contractor (especially since you do a lot of ADU and addition work):
If the lot is near wetlands or buffer zones, conservation approval can still be required.
Bottom line for your ADU projects
As of February 2, 2025 in Massachusetts:
✔ One ADU per single-family lot
✔ Maximum size: 900 SF
✔ Interior, attached, or detached ADUs allowed
✔ No special permit or zoning hearing required
✔ Standard building and environmental permits still required