ADU types explained

What California law means by an ADU

State law defines an ADU as an attached or detached residential unit with complete independent living facilities for one or more people, on a lot with a proposed or existing primary residence. It includes permanent provisions for living, sleeping, eating, cooking and sanitation. (Gov. Code §66313)

Garage or existing-space conversion

An existing garage or other structure becomes living space. Because the structure is already there, the question is its condition: the slab, walls, roof, insulation and how plumbing can reach it.

State law says no setback may be required for an existing structure converted to an ADU, or one rebuilt in the same location and to the same dimensions (Gov. Code §66314(d)(7)). It also says that when a garage is converted to an ADU, the city may not require the lost off-street parking spaces to be replaced (Gov. Code §66314(d)(11)).

Attached ADU

A new unit built against the house, with its own entrance, kitchen and bathroom. It suits lots where the yard is limited but there is room beside or behind the house. It is not the same as a home addition: an addition makes your home bigger, while an attached ADU is a separate dwelling reviewed under ADU rules. Separation from the main house, entrances and utilities need early attention.

Detached ADU

A standalone small home in the yard. It gives the most privacy between households and needs the most yard space, clear access for construction and a route for utilities from the street or the main house. For a new ADU that is not a conversion, state law limits required side and rear setbacks to no more than four feet (Gov. Code §66314(d)(7)).

Junior ADU (inside the house)

A junior ADU is no larger than 500 square feet of interior living space and is contained entirely within a single-family home. It may have its own bathroom or share one with the house (Gov. Code §66313).