
 Mass Construction Show
 Mass Construction Show Can You Build Your ADU?
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 Oct 7, 2025  Ashley Duval, a planner and law student specializing in land use, dives into Massachusetts' ADU legislation. She explains what Accessory Dwelling Units (ADUs) are and the legal framework guiding their construction. The discussion touches on the Affordable Homes Act, the chaotic rush of towns to draft bylaws, and the Attorney General's review of municipal regulations. They clarify that owner-occupancy isn’t required and outline challenges homeowners face in permit processes, revealing that while the interest in ADUs is growing, hurdles remain. 
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ADU Definition And Size Cap
- Massachusetts defines ADU as a self-contained unit with sleeping, cooking, and sanitary facilities and a separate entrance.
- Size is capped at 900 sq ft or half the principal dwelling, whichever is smaller.
ADUs Placed Under 40A Section 3
- The law placed protected ADUs into MGL 40A Section 3, making them an as-of-right use like schools or churches.
- That protection restricts towns from outright prohibiting ADUs and limits discretionary denial.
AG Reviews Found Wide Rejection
- Ashley reviewed about 40 Attorney General decisions and found only one town fully approved its bylaw.
- Many towns copied state regs and most AG reviews partially denied or struck sections as conflicting.
