What the Massachusetts AG ADU Decisions Mean for Builders and Homeowners
- 3 days ago
- 4 min read
A conversation with Avi and Alex from FutureLot's policy and legal team
If you're a builder or homeowner in Massachusetts trying to figure out what is possible on a specific lot, reading your town's ADU bylaw is no longer enough. The Massachusetts Attorney General has reviewed local ADU bylaws across the state and struck down a significant number of provisions that towns assumed were valid. The results are surprising, and in many cases, they work in homeowners' and builders' favor.
FutureLot's Avi sat down with Alex from the company's policy and legal team to break down five of the most important findings from those AG decisions. Here's what you need to know.
The Number of Struck Provisions Was Shocking
The first thing Alex made clear is just how widespread the problem was. Across towns throughout Massachusetts, the Attorney General found provision after provision that appeared completely valid on its face but was unenforceable under state law. Floor area ratio requirements for ADUs. Restrictions on which dwelling types could include ADUs. Provisions that towns had written into their bylaws in good faith and enforced without question.
The core lesson is one that FutureLot was built around: truly understanding what you can build on a lot in Massachusetts is not as simple as reading the local bylaw. State law layers on top of local regulations, and in many cases it overrides them entirely. A builder or homeowner who stops at the town bylaw may be leaving significant building rights on the table.
Towns Cannot Limit the Number of Bedrooms in an ADU
One of the clearest examples of overreach came from Auburn, where the town's bylaw capped ADUs at a maximum of one bedroom. On its face, this might seem like a reasonable local planning decision. The Attorney General disagreed.
The reasoning follows a principle already established for single-family homes: a town cannot regulate the interior of a residence. Just as a town cannot tell a homeowner how many bedrooms their house can have, it cannot tell them how many bedrooms their ADU can have. The AG struck down Auburn's bedroom cap on exactly these grounds.
For builders, this has a practical implication. If a client's town is enforcing a one-bedroom cap on ADUs, that restriction may not be valid. It is worth checking against current state law before accepting it as a constraint on a project.
ADUs Are Not Limited to Single-Family Homes
Another widely held assumption that the AG decisions disrupted: the idea that ADUs can only be added to single-family homes.
Windsor had written this restriction directly into its bylaw, limiting ADUs to single-family residences only. The Attorney General struck it down. Similar provisions in Stockbridge and Mount Washington were also struck.
The current rule in Massachusetts is broader than most people realize. If a property is located in a zone that allows single-family uses, the owner is permitted by right to add an ADU, regardless of whether the existing building is a single-family home, a two-family, or a three-family. The building type does not disqualify you.
For builders, this opens up a meaningfully larger pool of eligible projects than a strict reading of local bylaws might suggest.
Condo Owners May Be Eligible Too
This is the question Avi describes as the "gotcha question" that turns out to be genuinely important, especially in the greater Boston area where a large number of multi-family properties have been converted to condos.
The question: if you own a condo in a residential zone that allows single-family homes, can you build an ADU?
The Attorney General addressed this directly through a case in Bellingham, where the town's bylaw prohibited ADUs in condominiums. The AG struck it down. The reasoning points to a foundational principle of zoning law: you can regulate the type of building, but you cannot regulate the legal ownership structure of that building. State law allows ADUs on any principal dwelling. A condo is a principal dwelling. Ownership form doesn't change that entitlement.
For the many condo owners in Massachusetts who assumed they were categorically excluded from ADU eligibility, this decision is significant.
Basement Calculations: Finished or Not, They Count
The fifth area where towns got it wrong is one of the most technically nuanced but practically important: how gross floor area is calculated when determining ADU size limits.
Massachusetts ADU law generally allows an ADU up to 50 percent of the gross floor area of the primary dwelling. How that floor area is calculated matters enormously to whether a project is compliant. The state's definition includes basements, whether they are finished or unfinished.
Towns that tried to work around this found themselves overruled. Windsor attempted to exclude basements from the gross floor area calculation entirely. The AG struck it down. Athol tried a more targeted approach, counting only legally finished basements and excluding unfinished ones. The AG struck that down as well.
The practical implication for builders is significant. A project that appears to exceed size limits under a town's calculation method may be fully compliant under the state's definition. If a town is excluding basement square footage from gross floor area, that exclusion may not be valid, and the effective size limit for an ADU on that lot may be larger than the town is representing.
What This Means for Builders and Homeowners
Taken together, these five findings point to the same conclusion: in Massachusetts right now, the gap between what towns say you can build and what state law actually allows you to build is real, significant, and frequently in the homeowner's favor.
That gap is also exactly why tools like FutureLot exist. Reading a local bylaw and stopping there is no longer sufficient. Understanding what's enforceable requires knowing how the AG has interpreted state law and how those interpretations apply to a specific lot in a specific town.
FutureLot tracks all of it. For Massachusetts builders and homeowners ready to understand what they can actually build on their property, the starting point is futurelot.com.
