Does Contra Costa County, CA have its own adu rules ordinance?

No. Contra Costa County, CA does not appear to have a local adu rules ordinance, California state law applies instead. The rules summarized on this page come from CA Gov Code 65852.2.

Key Facts Ordinance Text Full Breakdown Violations FAQ Sources More in Contra Costa County

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

Light Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified June 2026

ADU rules in Contra Costa County, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Code Section: Chapter 82-24
Min Lot Size: 6,000 sq ft (10,000 in Kensington)
Max Detached Size: 1,000-1,200 sq ft
Max Height: 35 ft (14 ft in Kensington)
Short-Term Rental: Prohibited

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in California under recent ADU streamlining laws. The Contra Costa County, CA rules below cover local size, height, and setback requirements.

Summary

Unincorporated Contra Costa County allows one accessory dwelling unit (ADU) on lots of at least 6,000 sq ft in single-family, multi-family, P-1, and agricultural districts under Chapter 82-24 of the County Ordinance Code.

City-specific rules exist: Antioch, Brentwood, Richmond, and San Ramon have their own adu rules rules that differ from Contra Costa County's county-level regulations. If you live in one of those cities, check the city-specific page instead.

One accessory dwelling unit may be located on any lot in a single-family residential district (R-6, R-7, R-10, R-12, R-15, R-20, R-40, R-65, and R-100), planned unit district (P-1) for residential uses, or a multiple-family residential district (M-6, M-9, M-12, M-17, and M-29).

Source: CA Gov Code 65852.2View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Ordinance Code: Supplement 103).

Full Breakdown

Per Contra Costa County Ordinance Code Chapter 82-24 (Accessory Dwelling Units), one ADU may be located on any lot in the R-6, R-7, R-10, R-12, R-15, R-20, R-40, R-65, or R-100 single-family residential districts, the P-1 planned unit district for residential uses, the M-6, M-9, M-12, M-17, or M-29 multi-family residential districts, or the A-2, A-3, A-4, A-20, A-40, or A-80 agricultural districts. The minimum lot size for a property with a primary residence plus an ADU is 6,000 sq ft countywide (10,000 sq ft in the Kensington -K combining district).

Detached ADUs may be up to 1,000 sq ft in R-districts on lots under 12,000 sq ft, or up to 1,200 sq ft in agricultural districts and on R-district lots of 12,000 sq ft or larger. Maximum height is 35 feet countywide (14 feet in Kensington). A permanent foundation is required, and the exterior must be architecturally compatible with the primary dwelling. 008, ADUs are not allowed to be permitted for Short Term Rental Use.

Violations & Fines

Building or occupying an unpermitted ADU is a zoning violation enforced by the Department of Conservation and Development. Code enforcement can issue notices to comply, abatement orders, and administrative fines under Title 1 of the County Ordinance Code, and unpermitted structures may be required to be removed or brought into compliance.

Frequently Asked Questions

Can I rent my ADU on Airbnb in unincorporated Contra Costa County?

No. Per Contra Costa County Ordinance Code § 82-24.008, accessory dwelling units are not allowed to be permitted for Short Term Rental Use. Long-term rentals (typically 30+ days) are permitted.

What is the minimum lot size for an ADU?

Countywide the minimum lot size for a parcel with both a primary residence and an ADU is 6,000 sq ft. In the Kensington (-K) combining district the minimum is 10,000 sq ft, and detached ADUs there are capped at 14 feet in height.

Do I need a separate entrance for the ADU?

Yes. Per § 82-24.012, the ADU must have a separate entrance located on the building side or building rear, or not visible from the street, or otherwise subordinate to the primary residence.

Sources & Official References

Other rules in Contra Costa County

Shed & Carport RulesSome Restrictions ADU Rental RestrictionsSome Restrictions Garage ConversionsSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Parking Rules: EV ChargingSome Restrictions Building Setbacks & Zoning: Lot Coverage LimitsSome Restrictions Short-Term Rentals: Night CapsSome Restrictions Short-Term Rentals: Host Presence RuleSome Restrictions

All Contra Costa County rules

How Contra Costa County compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Contra Costa County to another location·View the California accessory structures overview

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ADU Rules in Cities Across Contra Costa County

Concord, CA Richmond, CA Antioch, CA San Ramon, CA Pittsburg, CA Walnut Creek, CA Brentwood, CA Oakley, CA Martinez, CA