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Statewide zoning could boost accessory dwelling unit construction

Healey’s proposal is expected to add 8,000 ADU units.

An accessory dwelling unit that Carol Brenner built for her sister in her Falmouth backyard.Carol Brenner

When Carol Brenner and her husband moved to Falmouth three years ago from Virginia seeking a more liberal political climate, they reached out to town officials to see if they could get permission to build another small unit behind their single-family Cape-style home about 10 minutes from the beach. They wanted to build a one-bedroom unit — about 750 square feet with a den and an open concept kitchen/living room — for Brenner’s sister, 74, who was living in Oregon and wanted to be near family as she aged.

Such small, add-on living spaces — known in real estate jargon as accessory dwelling units — have caught on as a potentially easy way to add more desperately needed homes in housing-starved places like Massachusetts. Encouraging more of them is a major feature of Governor Maura Healey’s new housing plan, which she unveiled Wednesday and which would override local zoning by requiring all municipalities in the state to allow homeowners to add such apartments.


Brenner’s experience is both a testament to why add-on units are so appealing to state officials — she eventually succeeded, and her sister just recently moved into a small standalone structure — and a warning of the pitfalls if the rules are not well crafted. As the Legislature considers Healey’s proposal, it needs to make sure that towns not only allow accessory dwelling units but aren’t able to impose so much red tape that few are actually built.

In Brenner’s case, town officials reassured her that accessory dwelling units were allowed in Falmouth. She just needed to get a special permit. But, Brenner said, the approval process for that permit still took nearly a year and required her to make her case at multiple public meetings. There was no opposition to the building among neighbors or town officials, and neighbors came to meetings to support her. But there were issues related to whether another septic system was needed, questions about a mobile coffee shop Brenner considered opening, and concerns about whether sheds could remain on the property.


“Everyone in the town of Falmouth was super helpful, but it’s such a red tape bureaucratic way of doing things,” Brenner said.

In towns across Massachusetts, a similar story emerges: Even in places where accessory dwelling units are legal on paper, they’re scarce on the ground because of the torturous approval process that few are willing to brave. In Greater Boston, where the state’s housing shortage is most acute, the promise of add-on units has been hampered by excessively complex rules.

Take Concord. The town has allowed accessory dwelling units since 1974. But for years, approval required a special permit. There were restrictions on lot and unit size, and the permit expired when the property was sold. In 46 years, just 52 permits were issued in a town of almost 20,000 people.

In 2020, seeking more development, Concord changed its zoning rules to allow accessory dwelling units of up to 750 square feet without the bureaucratic special permit process, as long as they met certain criteria. The town also made some rules about ADUs less restrictive. Since 2020, there have been 13 units permitted.

Concord Town Planner Elizabeth Hughes said the new bylaws allow a reasonable number of additional units to be built more easily. “There was definitely a fear that there was going to be this huge influx of additional dwelling units, but that really hasn’t been the case,” she said.


Healey’s proposal would authorize accessory dwelling units everywhere in the state and specify that they must be allowed by right — meaning, without the kind of approval process Brenner endured in Falmouth — if they measure less than 900 square feet. Healey administration officials estimate 8,000 new units could be created in five years. If her proposal becomes law, some of the most onerous types of local regulations would also be prohibited. Parking could not be required for a unit within half a mile of public transit and communities could not restrict occupancy to a homeowner’s relative.

But in Healey’s proposal, municipalities could still impose some regulations related to setbacks, height, parking, or short-term rentals — meaning, communities could ban rentals of ADUs through services like Airbnb.

The Legislature should carefully scrutinize the proposal, and the details will matter. Letting municipalities retain too much latitude would allow them to continue imposing requirements that are nearly impossible to meet. Lawmakers should ensure the state sets sufficient minimum requirements on what must be allowed “by right,” while leaving only limited discretion to municipalities.

In doing so, they can look to California as a national model: The state tried to legalize ADUs with a light touch but soon had to change course. In 2016, California passed a law requiring municipalities to allow accessory dwelling units. But many municipalities put strict restrictions on ADUs, like requiring occupants to be related to the homeowner or requiring multiple off-street parking spaces. Between 2019 and 2022, California passed additional laws stopping municipalities from imposing the most restrictive requirements. Before statewide legislation passed, California was issuing around 1,200 ADU permits annually. In 2019, there were around 12,000 ADUs permitted, and in 2022, there were over 24,000 permits approved, according to California’s Department of Housing and Community Development.


Oregon, Vermont, and Washington state all passed laws in the past few years making it easier to build ADUs. (Cities that have relaxed zoning regulations on their own volition and used ADUs to substantially increase their housing stock include Portland, Ore.; Seattle; and Vancouver, British Columbia.)

In Massachusetts, the Legislature should seek to pass legislation strong enough to end what is now a patchwork of local rules. A 2018 report by researcher Amy Dain, published by the Pioneer Institute, found that of 100 municipalities in Greater Boston, 37 allowed ADUs that could be rented and another 31 allowed ADUs only for relatives of the homeowner. (The rest had no ADU zoning at all.)

Communities have devised many tricks to make ADUs nearly impossible to build. In Burlington, according to Dain’s report, ADUs are allowed in houses that had at least 1,800 square feet of floor area in 1989. But few houses in the town were built that big before the 1990s. Belmont only allows ADUs in detached historic structures like antique carriage houses, which few homes have. Several communities, including Burlington, require two off-street parking spaces per ADU. The report found that, on average, only 2.5 ADUs are built each year in the municipalities where they are nominally allowed.


Restrictions that typically create the most barriers for new ADU housing are those that require a special permit, require parking, or require the owner to live in the primary house. Other common restrictions relate to minimum lot size, maximum unit size, architectural design, and restricting inhabitants to a homeowner’s relatives.

Changing just some of these restrictions can have a big impact. In Newton, for example, from 2008 to 2017, ADUs were allowed only by special permit with significant restrictions, and only 25 were permitted. In 2017, the city began allowing internal ADUs by right, eliminated a parking requirement, and eased rules regarding lot size. Over the next five years, 72 units were permitted.

The way that Newton and Concord relaxed their rules shows that some localities are genuinely trying to make ADUs work. Boston experimented with two small pilot programs, working with homeowners to understand the barriers to building ADUs. On Wednesday, Boston Mayor Michelle Wu proposed allowing internal ADUs — those inside an existing home — by right citywide and said the city is exploring a similar shift for detached units.

But there’s no substitute for a strong statewide policy. Rules for ADUs that are generally the same everywhere in Massachusetts should also attract more builders and lenders to create what is now still largely a bespoke product.

Today, traditional funding mechanisms are often not designed for smaller, less expensive accessory units. Units generally have to be custom designed.

If statewide standards increase the market for ADUs, that would also make it easier for banks to offer standardized products for financing small homes and for building companies to design standard, prefab small homes.

Chris Lee’s Brunswick, Maine-based construction company Backyard ADUs builds one-bedroom units of around 550 square feet costing about $200,000. Lee, who operates throughout Massachusetts, said his company has more demand than it can fulfill, but building is challenging because local planning boards “tend to create long arduous processes in order to get things approved.” Different municipal rules require builders to be familiar with each town’s process. “Knowing how to do it in Concord doesn’t help you do it in Newton,” Lee said. A statewide policy would be an important step toward changing that.

The bill’s passage is far from certain. Healey’s proposal is only the beginning of the legislative process, and municipalities tend to strongly resist curbs on local control of zoning laws. But municipalities have had nearly a century to show they can use their zoning powers for the common good. Healey, like her predecessor, has clearly come to the conclusion that it’s time to try something different.

Correction: An earlier version of this editorial misstated the number of parking spaces required for accessory dwelling units in Bedford.

Editorials represent the views of the Boston Globe Editorial Board. Follow us @GlobeOpinion.