Overview of Multifamily ADUs
ADUs unlock housing affordability in high-demand markets.
Accessory dwelling units (ADUs)
Accessory dwelling units (ADUs) are housing units built on residential properties. They are an accessory to a primary residence that have complete independent living facilities for one or more persons (including permanent provisions for living, sleeping, eating, cooking, and sanitation). They're also colloquially known as backyard homes, second dwelling units, guest houses, casitas, backyard cottages, mother-in-law units, and granny flats. There are many different types of ADUs, including detached structures located in a back or side yard, attached additions to a primary residence and conversion of existing structures (e.g. basements, parking garages, storage facilities). They range in size and configuration, spanning smaller studio units up to units with multiple bedrooms and bathrooms. California also allows for "junior" ADUs (JADUs), which are units that are under 500 SF that may include separate sanitation facilities or share sanitation facilities with the existing structure.
Evolution of ADU law in California
Evolution of ADU law in California - ADUs are not a "new" thing. In fact, California first passed SB 1160 in 1982 which encouraged local jurisdictions to legalize ADUs on single-family properties. In 2002, AB 1866 made efforts to further streamline the ADU process, but the regulatory framework continued to allow local jurisdictions to set their own standards for ADUs. This all changed massively in 2016 when California adopted SB 1069 and AB 2299 which streamlined the permitting process and set clear, reasonable statewide standards for ADUs which were implemented in 2017. Since then, several other laws have been passed to further close loopholes and enable a clear, unified statewide framework for ADUs. Notably, these include: SB 229 and AB 494 in 2017 (which clarified certain aspects of the law and gave California Department of Housing and Community Development ("HCD") oversight authority over how local jurisdictions permit ADUs; AB 670 in 2019 (which exempted ADUs/JADUs from restrictions in HOAs/CC&Rs), AB 3182 in 2021 (which further improved the permitting process standards), AB 2221 in 2022 (which closed a few more loopholes), and AB 976 in 2023 (which permanently exempted ADUs from owner-occupancy mandates).
As a result of all this policy, California (which is the nation's largest housing market) has led the way in recent years for ADUs by implementing a unified stateway ADU regulatory framework that provides clear guidelines for property owners to build ADUs throughout the state. The results speak for themselves:
- Between 2016 to 2023, the number of ADUs permitted in California has grown by 20x from 1,336 in 2016 (before the laws changed) with 26,924 ADUs permitted in 2023 (per HCD data).¹
- Over 1 in 5 homes permitted in California (21%) in 2023 was an ADU(per HCD data).²