Municipal zoning, permitting practices stall production

Even after statewide legalization in 2024, production of accessory dwelling units (ADUs) in Massachusetts remains far from that of other states due to local zoning and permitting practices that continue to discourage development, according to a new Pioneer Institute study.

“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,” said Andrew Mikula, author of “Beyond Legalization: How Regulatory Reform, Standardized Appraisals, and Public Engagement Can Multiply the Impact of Accessory Dwelling Units in Massachusetts.” “The state needs to keep iterating on its recent reforms to expand opportunities for homeowners to build ADUs.”

ADUs are small homes located on the same lots as larger “primary” dwellings. They are often backyard cottages, converted garages, or attic or basement apartments.

The West Coast has seen an explosion in the number of ADUs. In California, the number being permitted rose from 800 in 2014 to more than 30,000 in 2024. Today, a quarter of the new homes permitted there are ADUs.

Despite statewide legalization, Massachusetts, which estimates that it needs 222,000 new housing units over the next decade, saw only 550 ADUs permitted in the first half of this year. On a per capita basis, that’s less than half the number permitted in California.

"The new state ADU regulations are a massive step forward for homeowners who want to keep their extended families close by," said Buz Artiano, owner of BuildX, a custom ADU builder based in Carver. "But setbacks and septic rules kill a lot of potential projects, and permits are hard-won in some communities. Lawmakers could be doing a lot more to improve predictability and lower costs for my clients."

California achieved higher production rates thanks to a suite of zoning reforms enacted since 2016. Some of the reforms allowed the conversion of existing structures to ADUs by right, allowed ADUs in new construction, allowed multiple ADUs per property, and required municipal agencies to review permit applications within a set timeline.

Prominent housing advocates consider three attributes – by-right permitting, minimizing off-street parking requirements, and allowing non-owner-occupied arrangements – to be keys to unlocking ADU production.

Massachusetts currently prohibits “unreasonable requirements” for ADU development. Rather than trying to determine whether individual municipal provisions are unreasonable, Mikula recommends statewide standards for policies like setback regulations or the percentage of a lot that can be built upon.

The study also recommends that:

• Municipalities should eliminate parking requirements for ADUs and make site plan review criteria as clear and objective as possible.
• The Commonwealth should allow ADUs to be sold separately from the principal dwelling and remove the special permit requirement for having multiple ADUs on a lot.
• Lenders should require ADU training for appraisers and others to catalog and value ADUs in a systematic and data-driven way.

Finally, Boston must quicken its pace of ADU development for Massachusetts to meet its housing goals. On the West Coast, ADU development is concentrated in cities. Seattle has 9.6 percent of Washington’s population but accounted for at least 40 percent of the permits issued for ADUs between 2011 and 2023. Between 2016 and 2022, Los Angeles permitted 22 times more ADUs on a per capita basis than Boston has in the last six years.

Boston is exempt from the Commonwealth’s Zoning Act, which was amended in 2024 to allow ADUs more broadly. The city’s reform attempts are taking longer and don’t necessarily align with the rest of the state.

Andrew Mikula is a Senior Fellow in Housing at Pioneer Institute. Beyond housing, Andrew’s research areas of interest include urban planning, economic development, and regulatory reform. He holds a Master’s Degree in Urban Planning from the Harvard Graduate School of Design.

About Pioneer Institute: Pioneer empowers Americans with choices and opportunities to live freely and thrive. Working with state policymakers, we use expert research, educational initiatives, legal action and coalition-building to advance human potential in four critical areas: K-12 Education, Health, Economic Opportunity, and American Civic Values.

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