Contra Costa County, CA Accessory Structures: Garage Conversions (2026)

Per Contra Costa County Ordinance Code Chapter 82-24, an ADU attached to a primary residence may be created as an internal conversion of a garage or other area within the existing primary residence, or as an addition to the existing primary residence. The County (consistent with California Government Code § 65852.2) does not require a setback for an existing garage that is converted to an ADU. A lot containing an ADU must provide one additional off-street parking space to serve the ADU, except where parking is exempt under state law (e.g., within one-half mile of public transit). When a garage, carport, or covered parking structure is demolished or converted in conjunction with construction of an ADU, the displaced parking space must be replaced only if necessary to comply with the off-street parking requirements applicable to the primary dwelling unit. All converted garages must still meet building code requirements for habitability (ventilation, egress, fire separation, foundation) under the California Residential Code as adopted by the County.