Evaluating California's Accessory Dwelling Unit Reforms: Preliminary Evidence and Lessons for State Governments

Since 2016, California has adopted several laws to facilitate the development of accessory dwelling units (ADUs), which are secondary units on residential parcels. This paper analyzes ADU permitting in the Bay Area and southern California under the newly liberalized legal regime. It uses statistical models to describe the geography of ADU development and to identify the parcel-, neighborhood-, and jurisdiction-level characteristics that are associated with ADU permitting. These analyses indicate, among other findings, that ADUs represent a substantial share of recent housing permits, that ADUs are typically permitted on parcels with relatively good access to jobs, and that the relationship between a neighborhood’s ethno-racial composition and the prevalence of ADU permitting varies by county. In addition to providing guidance for state and local governments seeking to understand the likely payoff from liberalizing ADU regulation, our analyses and statistical models can help California’s housing department—which is charged with policing cities’ ADU regulations—to set priorities for enforcing the new laws.