In the first year after Massachusetts legalized accessory dwelling units statewide, more than 1,600 people applied for permits to build one — at least triple how many might have been built otherwise, according to a new report.
Of those, at least 1,200 received permits and many are already under construction, according to the report by Boston Indicators and Abundant Housing Massachusetts.While that’s a strong step, it still falls short of what will be needed to meet the state’s housing production goals.
“Thousands of people in our communities are solving problems in their lives, building ADUs and moving into new ADUs,” researcher and report author Amy Dain said during a webinar Wednesday morning. “These are homes people need in an urgent housing crisis.”
Before the law went into effect in February 2025, many cities and towns did not allow ADUs or placed a variety of restrictions on them. Some allowed ADUs built within an existing home, but outlawed detached units. Others did not allow ADUs to operate as rental units, only allowing property owners to build them for use by family members or caretakers.
Many towns also regulated the maximum size of an ADU, the minimum property area where one could be built and other dimensional aspects that made it difficult or even impossible to construct one without applying for zoning relief.
Under the new law, towns must allow ADUs of up to 900 square feet or half of the floor area of the primary home on the property, whichever is smaller.
The law allows communities to place “reasonable” restrictions on the design and construction of ADUs, and they can also enact their own ADU zoning that is more permissive than the state law, but they cannot create stricter rules than the statewide ones.
At least 217 communities permitted at least one ADU last year, according to state data, including some that had previously prohibited them. Though there is no data available on how many were permitted in previous years, Dain estimated that only a few hundred were being built statewide each year.
She said much of the success of the new ADU law was due to the fact that the state imposed it everywhere, rather than simply encouraging communities to allow ADUs or mandating that they create their own zoning town by town, as it did with 2021’s MBTA Communities Act.
The state has outlined a goal of building between 1,600 and 2,000 ADUs per year over the next five years. The report outlined a slew of current barriers that could make it difficult to reach that number.
Building codes, fire codes, energy codes, stormwater and wetlands regulations and septic system codes generally are designed to govern larger homes and other construction, not ADUs, according to the report. Because of this, some of the rules that might make sense for a house or apartment building are unnecessary and simply serve to drive up costs.
“The environment is not the developer’s enemy, but risk is. And our local regs right now add a lot of risk to development projects,” Dain said.
The biggest issue, however, is inconsistency from town to town, according to the report. Chris Lee, head of design and development at construction company Backyard ADUs, said he had done projects throughout Massachusetts, and every single community had different rules and a different permitting process.
Because of this, he said, each project has to have a team of experts to navigate the bureaucratic red tape. But when they’re done, they can’t even use what they’ve learned on the next project, because they’ll be dealing with a completely different set of rules.
The process and diverse regulations can add hundreds of thousands of dollars to the construction cost, Lee said.
The report recommended statewide standardization of building and fire codes, wetlands and stormwater regulations and other barriers that make it harder to get new housing built.
“I think we’d be doing twice as many ADUs as we are right now if we weren’t trying to figure out how to service every town of 5,000 people en masse,” Lee said.