Coming to a Backyard Near You: What’s New with ADUs in 2020

For the last few years, the state has explored ways to encourage cities and counties to allow property owners to build more Accessory Dwelling Units (ADUs). State legislators view ADUs as low cost and low controversy—unlike other housing legislation, changes to state ADU laws have sailed through with relatively little opposition. However, as cities and counties move to implement the 2019 legislation, local communities are beginning to realize the magnitude of the potential impacts wrought by the latest changes. Initial observations suggest that the Legislature has unlocked the potential of adding a significant number of new units, but perhaps not without local impacts and community frustration.

As of the new year, local jurisdictions are now strictly limited in the conditions they can impose on ADUs. For certain categories of “streamlined” ADUs—a term not used in state law but helpful for discussion purposes—cities and counties must approve units that meet state-established specifications. For all other ADUs, local jurisdictions retain some discretion, though the Legislature has used a heavy hand in regulating local control for these as well. As state law also voided the vast majority of local ADU ordinances on January 1, 2020, jurisdictions are strongly encouraged to review and consider updating their municipal codes if they want to set standards in areas that have not been preempted by the State.

Rules for Streamlined ADUs Associated with Single-Family Dwellings

Under the new streamlined regulations, most ADUs proposed to be located “wholly within” existing single-family houses must be approved by local jurisdictions. As the name implies, these units must be located completely within an existing home or accessory structure, such as a garage. Such units must meet other limited requirements, such as having direct exterior access and side and rear yard setbacks sufficient for fire safety. Alternately, property owners may elect to build a 500 square foot or smaller junior accessory dwelling unit (“JADU”) pursuant to Government Code 65852.22, though it is unclear how many property owners will elect to proceed under these more stringent requirements.

More surprisingly, the new state law also allows property owners to build “new detached” ADUs on the lot of an existing or proposed single-family residence. Again, if the ADU meets relatively minimal standards—including being new construction, detached from the main house, less than 16 feet high, smaller than 800 square feet, and outside of four-foot side and rear yard setbacks—a local jurisdiction must approve it. Cities and counties should note that even single-family homes with existing JADUs may add an ADU that complies with these guidelines. Anecdotal reports indicate that numerous businesses are already targeting property owners with standard plans or prefabricated dwelling units that automatically meet these requirements.

Rules for Streamlined ADUs Associated with Multi-Family Dwellings

The 2019 legislation also provides streamlined ADU options for owners of multi-family dwellings. First, property owners can convert non-livable space—such as storage rooms, garages, and attics—to new dwelling units. Property owners are entitled to at least one “non-livable space conversion” ADU or up to 25 percent of the number of existing units, whichever is greater.  For example, a duplex could convert an on-site garage to an additional unit. Similarly, a multi-family property with eight apartments could convert both a garage and an attic to ADUs, for a total of two.

Multi-family property owners are also eligible for “new detached” ADUs. Just like the new detached ADUs for single-family dwellings, these ADUs must involve new construction, be detached from the main dwelling, and be located outside of four-foot side and rear yard setbacks. Surprisingly, the legislature did not impose a size limitation on such structures for multi-family properties; jurisdictions might consider imposing a definitional limitation on the square footage of such structures.  

Rules for Other ADUs: Some Discretion Remains

Despite the sweeping changes, cities and counties maintain some discretion for attached ADUs, larger ADUs, and ADUs that do not otherwise meet the streamlined standards. For example, local jurisdictions may continue to set some limits on the maximum size of ADUs that don’t meet the new guidelines for whatever reason; as a general rule, one bedroom/studio ADUs may be limited to 850 sq. ft. while multi-bedroom units may be limited in size to 1,000 sq. ft. Cities also have the option to require a maximum of one parking space per ADU under certain conditions, but this option will not apply, for example, if transit options are available in close proximity or if the unit will be built at the same time as the main dwelling.

To continue to apply jurisdiction-specific development standards to such ADUs, however, local jurisdictions must adopt a “compliant ordinance.” At a minimum, the ordinance must regulate non-streamlined ADUs in a manner compliant with state law. However, given the confusing and somewhat contradictory state legislation, cities and counties may also want to outline the standards and processes for streamlined ADUs to assist the public as well as planning staff and decisionmakers. ADU ordinances must be submitted to the Department of Housing and Community Development within 60 days of adoption. 


Under the new legislation, cities and counties are no longer allowed to charge impact fees for ADUs that are less than 750 sq. ft. in size but may impose fees on larger units in proportion to the primary dwelling on a square footage basis. While the intent of this requirement is clear—to reduce fees for ADUs based on their smaller size—strict compliance with the proportion requirement may lead to local jurisdictions charging different impact fees for identical ADUs, because the size of the primary dwelling is different.

ADUs Count Toward RHNA

For jurisdictions that lament these new restrictions, it’s worth noting that all ADUs may be counted toward a jurisdiction’s regional housing needs assessment (RHNA) targets, which may make it easier for municipalities to comply with state housing law. However, whether increased development of these units actually leads to increased supply and decreased housing costs—and not just expansion of pool houses, playrooms, and au pair units—remains anyone’s guess.

For more information, contact SMW attorney Sara A. Clark

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