Contra Costa County · ADU permit data · Updated 2026-10-20
6.2months median, application to building permit, 2023–2025
That is about the same as the Bay Area median of 6.0 months. One in four applicants waited more than 9.6 months.
ADUs permitted in 2023–2025, 215 matched on parcel number. Includes time owners spent revising plans.
Source: California HCD Annual Progress Reports, filed by Contra Costa County
Fast quarter, median and slow quarter, in months
Unincorporated Contra Costa County 4.1–9.6 mo
Contra Costa County
Bay Area 3.8–10.5 mo
Median Fast quarter to slow quarter
Median wait
Where Uninc. Contra Costa Co. sits among 52 ranked cities
Uninc. Contra Costa Co. Other ranked cities Bay Area 6.0
Unincorporated Contra Costa County
6.2months
median wait, 2023–2025
State law gives the city 60 days to act once an application is complete. Counted from first submission, this share of ADUs took longer. Ask for the completeness letter, which is due within 15 business days, and keep its date.
Source: HCD Annual Progress Reports, 2023–2025; Gov. Code 66317
Unincorporated Contra Costa County
97%
of matched ADUs
One applicant in four took longer than this. Plan on it if the city sends your plans back for another round of corrections.
Source: HCD Annual Progress Reports, 2023–2025, 75th percentile
Unincorporated Contra Costa County
9.6months
One applicant in four had a building permit within this time from first submission.
Source: HCD Annual Progress Reports, 2023–2025, 25th percentile
Unincorporated Contra Costa County
4.1months
Source: units by calendar year, as reported by Contra Costa County to California HCD
Unincorporated Contra Costa County, units per year
ADU permits a year, 2023–2025 average
ADU permits a year per 1,000 houses, 109 places
Uninc. Contra Costa Co. Other Bay Area places
Unincorporated Contra Costa County
116a year
ADU permits, 2023–2025 average
Of every home Unincorporated Contra Costa County permitted in 2023–2025, this share was an ADU.
Source: HCD Annual Progress Reports, 2023–2025
Unincorporated Contra Costa County
34%
Permits a year for every 1,000 detached houses, so small and large cities can be compared.
Source: HCD Annual Progress Reports; DOF housing estimates
Unincorporated Contra Costa County
2.3
rank 56 of 92
Yearly ADU permits in 2023–2025, up 62% from 2019–2021.
Source: HCD Annual Progress Reports
Unincorporated Contra Costa County
+62%
Median time from building permit to certificate of occupancy for ADUs finished in 2023–2025. Add it to the permit wait for a full timeline.
Source: HCD Annual Progress Reports, 2023–2025
Unincorporated Contra Costa County
13.3months
median of 238
One ADU in four took longer than this to reach a certificate of occupancy after the permit.
Source: HCD Annual Progress Reports, 2023–2025, 75th percentile
Unincorporated Contra Costa County
18.0months
Median Fast quarter to slow quarter Bay Area median, 6.0 months Number is the rank out of 52 cities
Every page in Contra Costa County: median wait where we can measure it, otherwise ADU permits a year
Timeline tool
Pick a start date and see the fast, likely and slow dates for Unincorporated Contra Costa County, from the numbers on this page.
Estimate my permit datesNext step
Answer a few questions about your lot and your plans. We point you to the right kind of help for an ADU in Unincorporated Contra Costa County: an architect, a permit-drawing team, or a design-build firm. About two minutes, no call list.
Find the right first callStart with the city's own rules: ADU rules and process.
Source: Bay Area ADU Permit Clock 2026, our analysis of the California HCD Housing Element Annual Progress Reports (data.ca.gov) filed by Contra Costa County, and DOF housing estimates. Wait times are matched on parcel number and include applicant revision time. The 60-day rule is in Government Code section 66317. How we measured it · See all 109 jurisdictions
For ADUs permitted in 2023–2025, the median time from application to building permit in unincorporated Contra Costa County was 6.2 months (190 days), based on 215 permits we could match. A quarter took longer than 9.6 months.
Unincorporated Contra Costa County issued 347 ADU building permits in 2023–2025, about 116 a year. ADUs were 34% of all new homes permitted there.
The median time from building permit to certificate of occupancy was 13.3 months for ADUs completed in 2023–2025.