Massachusetts homeowners can now add a second home to their property — by right. As of February 2, 2025, a sweeping state housing law makes accessory dwelling units (ADUs) legal in every community that allows single-family homes, without the special permits and discretionary approvals that blocked most projects for decades.
What changed
The reform comes from the Affordable Homes Act (Chapter 150 of the Acts of 2024), signed by Governor Maura Healey in August 2024. Under the new statewide standard, a homeowner can build one ADU of up to 900 square feet (or half the home’s gross floor area, whichever is smaller) in any single-family zoning district — with no special permit, no owner-occupancy requirement, and no neighborhood veto. Local bylaws that conflict with the law are unenforceable.
ADUs can be detached “backyard cottages,” garage or basement conversions, or attached additions. Towns may still apply reasonable rules — setbacks, building code, septic — and can restrict short-term (Airbnb-style) rentals.
Why the state did it
Massachusetts needs at least 222,000 new housing units by 2035, according to the state’s housing plan, and the median single-family home now sells for $638,000 statewide — and $799,000 across Greater Boston. ADUs are the state’s bet on “gentle density”: more homes inside existing neighborhoods. The Executive Office of Housing and Livable Communities projects 8,000–10,000 ADUs over five years.
New financing
In March 2026, MassHousing opened a dedicated ADU loan — up to $250,000 for a detached unit and $150,000 for an attached one, for homeowners earning up to 135% of area median income.
Early uptake
One year in, Massachusetts cities and towns had approved 1,224 ADUs across 217 communities — a modest but growing start that mirrors the early years of California’s ADU boom, where annual permits climbed from about 800 in 2014 to more than 30,000 a decade later.
What it means for you
For homeowners, an ADU can mean rental income that offsets a mortgage, a place for an aging parent or an adult child, or added long-term flexibility. The economics and the rules vary by town and by project type.
Read our complete, fact-checked breakdown: Building an ADU in Massachusetts — costs, financing, rules & ROI. Wondering whether your property is a candidate? Contact Steven Novak at the Brody Murphy Novak Team — steve@bmnboston.com or 617-955-2224.