El Cerrito, CA Accessory Structures: ADU Rules (2026)

Contra Costa County adopted ADU Ordinance 2020-16 (Chapter 82-44) to conform to state ADU law. Every residential lot with an existing or proposed single-family dwelling may add one accessory dwelling unit plus one junior ADU (JADU up to 500 sq ft within the existing dwelling). Detached ADUs up to 800 sq ft, 16 feet tall, with 4-foot side and rear setbacks must be approved ministerially, regardless of base-zoning standards on lot coverage or FAR. Larger ADUs (up to 1,200 sq ft) are allowed but subject to lot coverage and FAR. Conversion ADUs (within existing garage, basement, or interior) have no size limit other than the existing structure. The county must issue a permit decision within 60 days of a complete application. No impact fees may be charged for ADUs under 750 sq ft. ADUs over 750 sq ft may only be charged fees proportional to the main dwelling size. Owner-occupancy is not required for ADUs permitted between 2020 and 2025, but JADUs require owner-occupancy of either the JADU or the primary unit. No replacement parking is required when a garage is converted to an ADU or when the property is within 0.5 mile of public transit. AB 1033 (2024) allows ADUs to be sold as condominiums if the county opts in (Contra Costa has not yet opted in as of recent updates—verify with DCD). Rentals under 30 days are prohibited (no ADU short-term rentals).