Accessory Dwelling Units (ADUs)

"Granny Houses"

An accessory dwelling unit (ADU) is a smaller, independent residential dwelling unit located on the same lot as a stand-alone (i.e., detached) single-family home. ADUs go by many different names throughout the U.S., including accessory apartments, secondary suites, and granny flats.


Technical Information

In 2017, Governor Jerry Brown signed two bills to promote the development of ADUs in California, which became effective January 1, 2018. This allowed ADUs to be built concurrently with the primary single-family residence along with easing parking restrictions and fees from utilities.

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.

 

The total area of floorspace of an attached accessory dwelling unit shall not exceed 50 percent of
the proposed or existing primary dwelling living area or 1,200 square feet.

  • 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.

 

The shortage of housing in some areas has put pressure on municipalities to allow ADUs. But these come with many restrictions depending on the area.

Where these units are permitted, there can be a variety of restrictions. Some areas only allow family members to live in the unit and in others, the primary homeowner must live in one of the two houses. There are restrictions on the minimum and maximum size of units, how many units are allowed on the property, how big the lot size must be and so on, depending on the municipality. Unlike tiny houses, they must meet the same regulations and codes as the primary residence. (Tiny houses are mobile and do not meet state and city codes.) In many cases the ADU must be sold with the original house.

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