Brentwood, CA Accessory Structures: Garage Conversions (2026)

Residential garages in Brentwood are governed by the California Residential Code Chapter 3. The garage-to-residence wall and any supporting walls must have not less than 1/2-inch gypsum board, and where the garage is beneath habitable space, 5/8-inch Type X gypsum must protect both walls and ceiling. The door between garage and residence must be a minimum 1 3/8-inch solid wood, solid or honeycomb core steel, or 20-minute fire-rated unit with self-closing and self-latching hardware. Garage floors must slope toward the door or a floor drain, and garage access openings must be at least 3 feet wide for a standard door or typically 16 feet wide for a two-car opening. Conversion of an attached or detached garage into an ADU or JADU is permitted ministerially under Government Code Section 65852.2, and the city cannot require replacement parking if the parcel is within 1/2 mile of a major transit stop or car-share vehicle. Non-conforming garage conversions that occurred without permits must be either permitted retroactively (with inspection and potential corrections) or reverted. Using a garage as a primary sleeping room without converting per code is a health and safety violation and creates insurance risk.