AUD article from http://www.hcd.ca.gov/policy-research/AccessoryDwellingUnits.shtml
What are ADUs?
Accessory Dwelling Units (ADUs) are known by many names: granny flats, in-law units, backyard cottages, secondary units and more. No matter what you call them, ADUs are an innovative, affordable, effective option for adding much-needed housing in California.
What are the benefits of ADUs?
ADUs are an affordable type of home to construct in California because they do not require paying for land, major new infrastructure, structured parking, or elevators.
ADUs can provide a source of income for homeowners.
ADUs are built with cost-effective wood frame construction, which is significantly less costly than homes in new multifamily infill buildings.
ADUs allow extended families to be near one another while maintaining privacy.
ADUs can provide as much living space as many newly-built apartments and condominiums, and they’re suited well for couples, small families, friends, young people, and seniors.
ADUs give homeowners the flexibility to share independent living areas with family members and others, allowing seniors to age in place as they require more care.
New laws effective January 1, 2018
Recent state legislation provides clarification and fee assistance for the creation of ADUs. Governor Brown signed two separate bills on October 8, 2017: SB 229 (Wieckowski) and AB 494 (Bloom).
These bills, effective January 1, 2018, clarify and improve various provisions of the law to promote the development of ADUs, including allowing ADUs to be built concurrently with a single-family home, opening areas where ADUs can be built to include all zoning districts that allow single-family uses, modifying fees from utilities, such as special districts and water corporations, and reducing parking requirements. Please see the HCD Technical Assistance Memorandum: Accessory Dwelling Unit Legislation (SB 229 & AB 494) (PDF), dated May 29, 2018, for further information.
Recent updates to state laws for ADUs
State legislation that took effect January 1, 2017 gave California cities more flexibility and latitude for allowing homeowners to build ADUs. Three separate bills were introduced and signed by Governor Brown; SB 1069 (Wieckowski), AB 2299 (Bloom), and AB 2406 (Thurmond). Each of these land use bills make it easier than ever for homeowners to take advantage of this attractive opportunity.