Can I build an ADU in my backyard?

In most cases, yes. Effective January 1, 2020, the governor of CA signed into law a new framework addressing the ongoing housing crisis in the state. The new law seeks to clarify and improve various existing provisions in order to promote the development of ADUs. These include allowing ADUs to be built concurrently with a single-family dwelling, opening areas where ADUs can be created to include all zoning districts that allow single-family and multifamily uses, modifying fees from utilities such as special districts and water corporations, limited exemptions or reductions in impact fees, and reduced parking requirements. Please see the Accessory Dwelling Unit Technical Assistance memo (PDF) for more information.