California ADU is a project by UC Berkeley’s Center for Community Innovation. The project was first established in 2019 to research ADU ordinances across the state to identify best practices for facilitating the uptake of California’s ADU enabling legislation. The first phase of this work was conducted from 2019-2021 and the second phase, with similar goals, but different methodology began in 2023.

This website features list of best practices, a list of the project’s ADU publications, and an interactive map-based visualization for exploring ADU permitting and production across the California. It also shares the findings of the first phase of the project in the previous research section.

Best practices from jurisdictions across the state including financing, pre-approved units, public information, and policies

Interactive map-based visualization of California ADU permitting and production from 2018-2022

Select publications from the Center for Community Innovation’s ADU research

Findings and jurisdiction grades from the 2019-2021 ADU research project

About Accessory Dwelling Units

Across the United States, but especially in California, communities are experiencing challenges in housing affordability. One potential solution is increasing the production of Accessory Dwelling Units (ADUs), also known as secondary units, granny flats, and in-law units, which are separate small dwellings embedded within residential properties. They can be created by taking space from an existing building, adding to an existing structure, or constructing standalone detached buildings. ADUs are a low-cost and readily implementable approach to infill development, particularly in high-cost cities characterized by little to no vacant land and an abundance of low-density development.
However, an assortment of barriers including a lack of ADU financing products, land use and zoning regulations, permitting bureaucracy, and overall high construction costs restrict the widespread development of ADUs in the state. Since 2016, the California State Legislature has passed a suite of new legislation aimed at facilitating the construction of ADUs in the state by easing certain restrictive zoning and land use regulations.

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