An example of Backyard ADUs’ accessory dwelling unit, installed at a property in Concord. While the company has a standard catalogue of designs, buyers can customize them. Photo courtesy of Backyard ADUs

While recent legislation has sought to increase accessory dwelling unit construction in Massachusetts, a new study from the Pioneer Institute shows that it has yet to occur.

In California, the poster child for using accessory dwelling units to rapidly grow the housing stock, permits for new ADUs hit 30,000 in 2024. A quarter of the new homes permitted in the state are ADUs, according to the study.

But Massachusetts saw only 550 ADUs permitted in the first half of this year, less than a quarter of the number OK’d in California on a per capita basis.

“Without actionable policy changes, young people will continue to leave Massachusetts in droves and many older adults will be trapped in large homes that no longer suit their needs,” Andrew Mikula, a senior fellow on housing at Pioneer Institute, said in a statement. “The state needs to keep iterating on its recent reforms to expand opportunities for homeowners to build ADUs.”

Massachusetts now allows ADUs by right and prohibits “unreasonable requirements” when looking to construct an ADU. Still, the study argues, more statewide policies governing setbacks and other rules would help increase the number of ADUs being built. The study also called for the elimination of parking requirements.

Additionally, Boston is currently exempt from the state’s new ADU law, as it’s governed by a different part of state zoning law, limiting ADU construction in the state’s biggest city.

The study calls on Boston to speed up its pace of ADU development to match cities such as Seattle and Los Angeles. These cities have seen an ADU development boom: Between 2016 and 2022, Los Angeles permitted 22 times more ADUs on a per capita basis than Boston has in the last six years, according to the study.