California ADU Reform: A Retrospective
How YIMBYs Helped Kick Off a California Building Boom
In 2016, California state policymakers established a statewide set of rules for legalizing accessory dwelling units (ADUs). Eight years later, and complemented by additional, follow-on ADU regulations, we can definitively say that this reform program has been an overwhelming success: YIMBY-supported ADU legalization has triggered a building boom, such that ADUs now comprise a large share of new housing produced in most cities.
The success of ADU legalization serves as a ready model, both for future land-use reforms in California and other states seeking to address the housing shortage.
What Has ADU Legalization Accomplished
The permitting data from the past eight years is unambiguous: ADU legalization triggered a building boom. According to permitting data compiled by HCD:
- The number of ADUs permitted each year in California increased by 15, 334% between 2016 and 2022, collectively resulting in 83, 865 ADUs permitted.
- Other than 2020—a year beset by the COVID-19 pandemic—ADU permitting has increased by 42 to 76% every year since 2016. There is little reason to believe that this growth in permitting will slow down any time soon.
- As of 2022, 19% of all housing units produced in California—or nearly one in five homes— is an ADU.
On February 8, 2024 California YIMBY held a webinar on our report, featuring our Research Director Nolan Gray and Ryan O’Connell, founder of How to ADU. You can view the hour-long webinar here!
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