Accessory Structures in Contra Costa County, CA (2026)

4 county-level rules, plus city-specific rules for 9 cities in Contra Costa County, California.

Verified from official government sources

Note: These county rules apply to unincorporated areas of Contra Costa County. If you live within an incorporated city, that city's own rules apply — see the city list below.

ADU Rules

Contra Costa County allows one ADU and one JADU on any residential lot by ministerial permit, consistent with AB 68/AB 881 and Gov. Code 65852.2. Detached ADUs up to 800 sq ft with 4-foot setbacks are permitted as of right, with 60-day review, no impact fees under 750 sq ft, and no replacement parking required near transit.

Accessory Structures: Adu Permits

Few Restrictions

Full ordinance details →Official source ↗

Shed Rules

In unincorporated Contra Costa, a detached one-story accessory building used as a tool/storage shed of 120 sq ft or less does not require a building permit. Zoning setbacks still apply—typically 3 feet from side/rear property lines in R-zones—and any shed with electrical or plumbing needs a permit.

Accessory Structures: Sheds

Few Restrictions

Full ordinance details →Official source ↗

Garage Conversions

Attached and detached garages in unincorporated Contra Costa must meet zoning setbacks and building code fire separation (1/2-inch gypsum from dwelling). Garages cannot be converted to living space without a permit, though garage-to-ADU conversions are streamlined under state law with no replacement parking near transit.

Accessory Structures: Garage Rules

Some Restrictions

Full ordinance details →Official source ↗

Carport Rules

Carports in unincorporated Contra Costa County are regulated as accessory structures under Title 8 (Zoning) of the County Ordinance Code and as covered structures under the California Building Code as adopted by the county. A carport must satisfy the yard-setback rules of the underlying residential zoning district (e.g., R-6 single-family per Chapter 84-4) and requires a building permit. The county's STR ordinance separately requires off-street parking and may restrict use of carports for STR guest parking.