ADU Rules in Contra Costa County, California
We track 3 cities in Contra Costa County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, Antioch has the lowest starting permit fees ($7,000 – $13,000).
Cities
3
Max Detached Size
1,000–1,200 sq ft
Build Costs From
$150,000
Pre-approved Plans
3 of 3 cities
Contra Costa County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| Concord | 1,200 sq ft | 16 ft (detached) | $8,000 – $16,000 | $170,000 – $340,000 |
| Antioch | 1,200 sq ft | 16 ft (detached) | $7,000 – $13,000 | $150,000 – $305,000 |
| Richmond | 1,000 sq ft | 16 ft (detached) | $7,000 – $14,000 | $160,000 – $330,000 |
Concord ADU rules
Concord offers six free pre-approved ADU plans, from a 205 sq ft studio to an 847 sq ft two-bedroom, and complete applications using them can be approved in as few as five days. The city also launched a rebate of up to $15,000 for ADU applicants in 2025, first come first served while funds last. Lots near BART or Clayton Road get an 18 ft detached height limit.
Antioch ADU rules
Antioch offers city pre-approved ADU plans: applications that use them are decided within 30 days and pay reduced plan check fees. Standard rules otherwise follow state law, with 16 ft detached and 25 ft attached height limits and 4 ft side and rear setbacks. Larger lots in newer east Antioch subdivisions leave the most room for detached units.
Richmond ADU rules
Richmond limits new detached ADUs to 850 sq ft for a studio or one-bedroom and 1,000 sq ft for two or more bedrooms, and requires 5 ft of separation from the main house. The city offers a preapproved ADU plans program and has permitted more than 370 ADUs since 2019. Lots near BART or ferry service can build to 18 ft.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.