ADUs in Mass. lag west coast a year after state law meant to spur construction

A new study from the Pioneer Institute reveals that Massachusetts continues to lag significantly behind California in accessory dwelling unit production, despite statewide legalization in 2024.

While California permitted over 30,000 ADUs in 2024 — representing a quarter of all new home permits — Massachusetts managed only 550 ADUs in the first half of this year.

On a per capita basis, Massachusetts permits fewer than a quarter of the ADUs that California approves.

The disparity highlights the effectiveness of California's comprehensive ADU reforms implemented since 2016, which have created one of the nation's most favorable environments for accessory dwelling unit development.

California's success stems from key regulatory changes including by-right permitting that eliminates discretionary review processes, streamlined approval timelines that require municipal agencies to process applications within set deadlines, and allowances for multiple ADUs per property.

The state has also minimized off-street parking requirements and permits non-owner-occupied arrangements, removing common barriers that previously discouraged development.

For California property owners and developers, the comparison underscores the competitive advantages the state has built into its ADU framework.

The dramatic increase from 800 permitted ADUs in 2014 to over 30,000 in 2024 demonstrates how supportive regulatory environments can unlock housing production potential, providing California homeowners with significantly more opportunities to add value to their properties while addressing the state's housing shortage.