On January 1, 2017, new California State laws took effect that greatly expanded the opportunities to build new ADUs or legalize existing ADUs. These rules also clarified, and in some cases standardized, important policy and procedure matters statewide to eliminate confusion. Some ADU requirements are set by the State, and others are set by local governments. Local governments may not create requirements for ADU parking, setbacks, and certain other standards that are more restrictive than what the State allows. Where local ordinances do not meet the basic requirements of State law, local governments must use State standards to process ADU applications.
On January 1, 2020, additional California State laws went into effect to further streamline the ADU building process. Collectively, the new laws allow almost every residential property in the state to build three units of housing—including in areas zoned for single family homes. The measures also further streamline permit processes by reducing fees and removing rules that used to inhibit the construction of ADUs, such as requiring homeowners to live on the same property as the ADU they want to build.