WHEN GOV. MAURA Healey rolled out her housing bond bill in 2024, she and housing advocates touted one policy change as low-hanging fruit: legalizing accessory dwelling units – sometimes known as in-law units or “granny flats.” The governor said the move could spur 8,000 to 10,000 new units across the state in five years.
One year after the final law passed, permitting is falling short. Massachusetts municipalities received more than 1,600 applications for accessory dwelling unit permits and issued more than 1,200 in the past year. That is a sizable increase from the few hundred ADUs constructed over the past decades through local policies, but falls short of what advocates say is needed, and short of the Healey administration’s own target of 1,600 to 2,000 units per year.
The barrier to a Massachusetts ADU boom is a combination of complex permitting processes, local wetlands and sewer regulations, and some municipal sour grapes, according to a new report from Boston Indicators and the advocacy group Abundant Housing Massachusetts.
“Legalization works, but don’t get too excited,” said housing researcher Amy Dain, the report’s author, at a virtual event on Wednesday. “I know I’m very enthusiastic about zoning reform, but this legalization was only a first step.” The leap in permits is encouraging, she said, but “there’s more work to be done.”
The report argues the permitting gap doesn’t reflect a lack of homeowner interest, but rather a regulatory system that was never designed to handle an influx of development of the small housing units across 351 cities and towns with their own set of permitting rules.
The lesson, the report says, is that the state should consolidate even more control — over zoning, building codes, fire codes, septic rules, wetlands standards, and stormwater requirements.
“Just passing strong state zoning reform to allow ADUs by right is not enough,” said Jesse Kanson-Benanav, executive director of Abundant Housing Massachusetts, which advocates for changes to make it easier to build more housing. “Even if, on paper, our law is stronger than some other states, the unique aspects of local control and fragmented permitting and regulatory oversight of new housing development in Massachusetts remains a barrier to achieving the full impact of the state ADU law that many of us in the housing advocacy community seek.”
Unlike the firestorm-inducing MBTA Communities housing law, which requires cities and towns near public transit to zone a multifamily housing district, the new ADU rules took effect statewide with passage of the law.
There was some grumbling about a one-size-fits-all approach, but about a third of municipalities amended their local zoning within the year to either go beyond the text of the new law or to make sure that the local law accurately reflected the new statewide policy.
The upside, according to researchers, is a clear effort to make the ADU process easier to navigate for homeowners. The downside, based on a review from the attorney general’s office, is a lot of inconsistency between municipal ADU ordinances. The attorney general’s office had to strike language in bylaws that tried to impose conflicting parking requirements or dimension standards, require special permits, or limit ADUs to lots containing single-family homes — they are legal in any district that allows single-family homes.
“I felt like that just further emphasized how confusing the whole system of local regulation is,” Dain said.
Boston, which is carved out of both the MBTA Communities law and the ADU law, has permitted more small units in the past year – 44 – than any other single municipality through its own limited ADU program. But as a proportion of existing homes, the report finds, “Boston looks less successful permitting ADUs than many other communities.”
The new law legalizes ADUs – small residential units with no more than 900 square feet of floor area, or half the floor area of the principal dwelling, whichever is smaller – on lots in “single-family residential districts.”
Under the statewide law, municipalities can still impose dimensional requirements on ADUs, including setbacks, the amount of area on a lot that a building can cover, requirements for leaving open space on a lot, building bulk and height, and number of stories.
As a baseline, municipalities are able to require that ADUs be built with the same distance from the property line as other accessory structures like garages. But if those standards make it impossible to build ADUs, Dain noted, the setback rule can be waived as “unreasonable.”
This creates a befuddling patchwork. The setback standards exist in local regulations but they are not written with the smaller detached residential structures in mind.
“To the property owner, that is a pathway to get a permit for a project, but it’s an uncertain pathway, and risk is not the friend of development,” Dain said. “It would be far better for the state to define dimensional standards for ADUs everywhere, standardize this for ADUs, and standardize setback requirements.”
The same philosophy should apply to septic systems and fire codes, speakers at the event said. Well over 100 cities and towns have specific local septic system regulations that can differ from state regulations on things like depth to groundwater, the required design flow for septic systems, how to count bedrooms for calculating flow-per-bedroom rules, and more.
Protecting wetlands is essential, Dain said, but she said another barrier to ADU development is the fact at least 130 municipalities across the state have local wetlands rules that exceed the protections of the state Wetlands Protection Act.
“Massachusetts has layered countless rules around zoning, wetlands, stormwater, fire safety, energy codes, and local approvals into a system that is extraordinarily difficult for even experienced developers to navigate, let alone ordinary homeowners,” said Luc Schuster, executive director of Boston Indicators. “If we’re serious about building new housing, we need to simplify this regulatory maze at both the state and local level.”
The high cost of construction is largely out of the hands of state lawmakers, Dain said, but code regulation isn’t. The researchers want to see consistent and improved regulatory standards, regionalized enforcement of codes, and increased cross-departmental coordination on the local and state scale.
Some webinar attendees expressed concern about the idea of changing statewide standards in a timely fashion and in a way that would provide adequate wetlands protection.
State wetlands regulations “are decades out of date in terms of the calculations used for designing stormwater systems,” said Heidi Ricci, director of policy and advocacy at Mass Audubon. Consistent state standards requiring significant technical analysis “sound good,” she said, “but is it feasible?”
A new report released by the Greater Boston Chamber of Commerce on Wednesday on boosting housing supply identifies ADUs as a potential opportunity being explored in Massachusetts and other states.
Neighboring New Hampshire, it notes, passed a policy in 2016 allowing homeowners to build one ADU by right or with a “minor permit.” New York City, as part of a broader housing reform package adopted in late 2024, created “a pathway to legalize previously unauthorized basement, garage and other ADU rental units.” California’s changes, the report states, “limits local governments’ power to impose standards on ADU construction.”
According to the Boston Indicators report, California went from roughly 1,300 ADU permits in 2015 to more than 30,000 in 2024, after waves of successive state reforms rather than a single legislative act.
Massachusetts has more than 3 million dwelling units, Dain said, so even 1,200 ADUs in a year is only “hundredths of a single percent of that, she said. “With further reform, we could gain tens of thousands of ADUs in a decade. That starts to make a big difference in meeting our statewide need for hundreds of thousands of homes.”
Healey has set a goal of 222,000 new housing units needed by 2035 to meet demand.
The report found 217 municipalities issued at least one ADU permit in 2025, but the majority are in the eastern part of the state. Parts of Western Massachusetts are an ADU dead zone, with many communities reporting no permitted ADUs, or not reporting back at all.
Chris Lee, CEO of Backyard ADUs, a company that specializes in modular construction, described the regulatory system from a builder’s perspective as deeply “fragmented.” He said it’s in large part because of the New England “home rule” tradition that means an array of different permitting processes across municipalities.
Unexpected septic system or wetlands rules, for instance, can introduce significant project costs, he said. Building an ADU one town over can suddenly mean a $100,000 higher price tag.
ADU builders in California, Seattle, and Texas “get to deal with a single group, with a single permitting and inspection culture for millions of people,” Lee said. In Massachusetts, “what it means for us on the ground is we’ve had to fight tooth and nail to build a design-build company that can service the entire state. And it just barely works, to be clear.”
