Contra Costa County, CA Accessory Structures: Shed Rules (2026)

California Building Code Section 105.2 (adopted by Contra Costa County) exempts one-story detached accessory structures used as tool and storage sheds, playhouses, and similar uses from a building permit if the floor area does not exceed 120 sq ft and the structure is less than 12 feet in height. Although permit-exempt, the shed must still comply with Title 8 (Zoning) of the Contra Costa County Ordinance Code. In typical single-family residential zones (R-6, R-10, R-15, R-20, R-40), accessory structures must meet minimum side and rear setbacks (generally 3 feet for sheds in residential zones, but greater in the larger lot zones), and the front-yard setback matches the main dwelling. Maximum lot coverage (35–40% in most residential zones) includes accessory structures. If the shed exceeds 120 sq ft, or has electrical service, plumbing, or mechanical equipment, a building permit is required regardless of size. In a Very High Fire Hazard Severity Zone, sheds within defensible space zones must be constructed of ignition-resistant materials or be located outside Zone 0 and 1. Prefabricated sheds sold at home-improvement stores typically comply with 120 sq ft thresholds but customers should confirm footprint and height.