On August 6, 2024, Governor Maura Healey signed the Affordable Homes Act into law — described by the Healey-Driscoll Administration as "the most ambitious housing legislation in the state's history." The ADU-specific provisions took full effect on February 2, 2025. As of that date, every Massachusetts homeowner with a single-family property has the right to build one ADU by right — no special permit, no owner-occupancy requirement, no local prohibition. In the law's first year, cities and towns permitted or approved 1,224 ADUs across 217 communities, per the state's February 2026 one-year update. Here's what the law actually says and what it means for you.
Under the Affordable Homes Act (Section 1A of Chapter 40A, General Laws), every municipality in Massachusetts must allow one ADU by right on any single-family residential lot. "By right" means no discretionary review, no special permit, no variance, no appeal process — just a building permit based on objective criteria like setbacks and size.
The law sets a maximum ADU size of 900 square feet OR 50% of the gross floor area of the primary dwelling, whichever is less. So on a 1,400 sqft home, the ADU maximum is 700 sqft. On a 2,000 sqft home, the maximum is 900 sqft (50% = 1,000 sqft but the law caps at 900).
The Affordable Homes Act explicitly prohibits municipalities from imposing owner-occupancy requirements. You do not need to live on the property to build or rent out an ADU anywhere in Massachusetts. Any local bylaw or ordinance requiring owner-occupancy became unenforceable as of February 2, 2025.
Municipalities may not require additional parking for an ADU located within half a mile of a transit stop. Outside that zone, limited parking requirements may still apply, but cities cannot use parking requirements as a de facto prohibition on ADU development.
The most comprehensive housing legislation in Massachusetts history. ADU provisions in Sections 7 and 8 amend the Zoning Act (G.L. c. 40A).
The Executive Office of Housing and Livable Communities releases draft regulations for public comment, providing guidance on implementation.
EOHLC's final ADU regulations published in the Massachusetts Register. Municipalities have a clear framework for implementation.
All single-family homeowners in Massachusetts now have the right to build one ADU by right. Any local prohibition becomes unenforceable.
Governor Healey announces survey data showing 844 ADU applications in 170 communities, with 550+ approvals as of July 2025.
The state's one-year update reports cities and towns have permitted or approved 1,224 ADUs across 217 communities since the law took effect — figures the state describes as an initial snapshot expected to grow as municipal reporting continues.
Massachusetts has some of the strongest ADU rental markets in the country. Boston metro average rent for a 1BR ADU runs $2,800–$3,500/month. Even suburban communities like Worcester, Springfield, and Lowell command $1,800–$2,400/month for well-designed ADUs. At current Massachusetts construction costs — roughly $180,000–$320,000, spanning garage conversions on the low end to new detached construction on the high end — the ROI math is compelling, particularly with no owner-occupancy requirement.
Massachusetts's aging population and high cost of assisted living ($8,000–$12,000/month in many facilities) makes the ADU-as-family-housing case particularly strong. An ADU built for $250,000 that keeps an aging parent close while maintaining privacy is often more economical than facility alternatives within 3–4 years.
While state law now floors what every municipality must allow, cities and towns can still regulate design compatibility, setbacks (within state minimums), and size (up to but not exceeding the state maximum). Check with your local planning department for current local standards — which should be updated to align with state law, though many are still in progress.
Get a free 2026 cost estimate for any ADU type in Massachusetts — detached, garage conversion, basement, and more.
Massachusetts ADU Cost Guide →