Impact of Accessory Dwelling Units Legislation - HUD User (.gov)

The federal Department of Housing and Urban Development is funding two major research studies to evaluate the effectiveness of California's recent accessory dwelling unit legislation, with results expected by spring 2026.

The University of California, Los Angeles and University of California, Irvine will conduct separate two-year studies examining how the state's ADU reforms have impacted housing production and affordability since implementation.

California's Housing Opportunity and More Efficiency Act, which took effect January 1, 2022, significantly reduced barriers to ADU construction by eliminating owner-occupancy requirements, streamlining municipal approval processes, and mandating that cities offer preapproved ADU plans.

These small, independent living units with full kitchens and bathrooms can be built as attachments to existing homes or as standalone structures on the same property.

The UCLA study will specifically analyze how ADU development has affected housing affordability by examining parcel-level data on single-family homes alongside neighborhood rental prices and land values, using ADU permitting data from the California Department of Housing and Community Development.

For California property owners and developers, these federally-funded studies represent a critical assessment of whether recent legislative changes are delivering on promises to increase housing supply.

The research findings could influence future housing policy decisions and provide data-driven insights into ADUs' potential as a solution to the state's ongoing housing shortage.