Building permits, zoning and land rules in Contra Costa County, California

Yes. Almost all projects in unincorporated Contra Costa County require building permits, including new structures, additions, remodels, utilities, decks, garages, accessory dwelling units and generators¹. The county lists the California building, residential, electrical, mechanical, plumbing, energy, fire and related codes among its current codes for unincorporated construction³. Limited exemptions include qualifying one-story detached accessory structures no larger than 120 square feet and agricultural or nursery shade-cloth structures without service systems^12,13. Owner-builders can pull permits, but must provide the required declarations and remain legally and financially responsible for the work¹⁴.

The Contra Costa County Department of Conservation and Development handles building permits and planning applications for unincorporated property from its permit center at 30 Muir Road in Martinez¹⁵. Call the Application and Permit Center at 925-655-2700 for building questions or the Planning Division at 925-655-2774 for zoning and land-use questions¹⁵. Applications and plans must be filed digitally through ePermits; paper submittals are no longer accepted⁴. Building permit fees are based on project valuation, while planning applications require a deposit with time-and-materials billing above it; both are listed in the Land Development Fee Schedule¹⁶. Permitted projects are inspected against the approved plans, and the permit and reviewed stamped plans must be onsite for inspection¹⁷. Septic and well matters go to Contra Costa Health's Environmental Health Division at 925-608-5500¹⁸. Richmond issues building permits for ADUs after city Planning approval¹⁹. Walnut Creek and Oakley handle their own building permits^20,21. Septic and well review stays with Contra Costa Health Environmental Health, including city properties⁵.

Contra Costa County zoning applies to unincorporated land; city parcels follow municipal zoning instead². Concord, Antioch, Richmond, Pittsburg, Walnut Creek, Brentwood administer their own zoning^{22,23,24,25,26,27}. Oakley, Town of Danville, Martinez, Pleasant Hill, San Pablo, Hercules also administer their own zoning^{28,29,30,31,32,33}. Richmond adopts zoning and subdivision regulations, while Concord Planning provides parcel zoning, permitted-use and development-standard information^22,24. Septic and well review remains with Contra Costa Health Environmental Health across city boundaries⁵. For an unincorporated parcel, ask county Planning to identify the district and applicable development plan before choosing a home site^2,15.

Contra Costa County agricultural standards distinguish lot dimensions from acreage per residential unit: the agricultural land-use matrix specifies at least 40 acres per unit on non-prime agricultural land and 10 acres per unit on agricultural land³⁴. The same matrix lists minimum lot areas of 40 acres in A-40 and 80 acres in A-80³⁴. The A-2 General Agricultural District separately requires at least 5 acres, 250 feet average width and 200 feet depth, subject to its stated exception; meeting these dimensions alone does not resolve residential density^34,35. Ask county Planning which acreage category and exceptions apply before relying on an agricultural parcel for a home or split; Current Planning reviews unincorporated subdivision applications under local and relevant state regulations and CEQA^2,15. Montalvin Manor P-1 lot area, coverage and height standards vary by table, and Discovery Bay P-1 setbacks are plan-specific^36,37. Qualifying urban housing developments have a separate 4-foot side and rear setback rule³⁸. We could not confirm a general minimum dwelling size; ask the Planning Division for parcel standards¹⁵.

Contra Costa Health Environmental Health reviews septic and well properties throughout the county, including cities⁵. Properties with septic systems and no public sewer need approved plans before building-permit application submittal; additions on septic properties also require prior Environmental Health approval⁵. Contra Costa Health requires a construction permit for new, replacement, altered or abandoned onsite wastewater systems, including conventional and alternative systems, vault privies and sewage holding tanks⁶. Permitted work requires inspections, final approval and written authorization before the system is changed from the approved plans or placed in service⁶. Vault privies and sewage holding tanks are permit categories, not permit-free sanitation options⁶. Only 0.5% of Contra Costa County's mapped soils are rated free of severe limitations for a conventional septic drain field, so evaluate the site and soil before relying on a standard system¹¹. Call Environmental Health at 925-608-5500 about the parcel and application¹⁸.

Sleeping or living in an RV or travel trailer is prohibited in unincorporated Contra Costa County unless a specific code exception applies; residential storage requires screening from public view and does not authorize occupancy⁷. Exceptions include lawful mobile-home or travel-trailer parks and land-use-permitted RV parks or campgrounds in designated districts³⁹. Separate mobile-home provisions allow qualifying hardship family occupancy by land-use permit, approved construction-office or watchman use, and approved interim agricultural use; these are conditional uses, not blanket permission to live onsite while building³⁹. Ask the Planning Division which exception, if any, fits the proposed vehicle and use¹⁵. Contra Costa County treats a tiny home on wheels as an RV, does not recognize tiny homes as a separate planning category, and prohibits permanently using that vehicle as a mobile home⁸. A permanent small-home option is an ADU: county Planning approval precedes the building application, with Environmental Health review on septic properties⁴⁰. A detached ADU up to 800 square feet and 16 feet tall receives streamlined processing without required parking; ADUs may not be permitted for short-term rentals⁴⁰. We could not confirm a complete private-land temporary-camping rule; ask the Planning Division before staying onsite¹⁵.

1. Confirm that the parcel is unincorporated, then ask the Planning Division for its zoning district, allowed residential use, setbacks and any special-plan standards^2,15.
2. Determine water and wastewater service; septic properties without public sewer, including additions on septic properties, need Environmental Health plan approval before the building application⁵.
3. If septic is needed, obtain the onsite-wastewater construction permit and plan for required inspections before putting the system into service⁶.
4. Check flood and drainage constraints; improvements in a FEMA Special Flood Hazard Area require a Public Works floodplain permit⁴¹.
5. Resolve legal road access and ask Public Works whether driveway work needs an encroachment permit⁴². A connection within a state-highway right of way requires a Caltrans encroachment permit⁴³.
6. Submit the application and plans through ePermits; an owner-builder must also submit the required declarations and ownership documentation^4,44.
7. Keep the permit and stamped plans onsite for required inspections, then complete the applicable final-inspection and occupancy process^17,45.

Start with jurisdiction and zoning: county zoning information covers unincorporated areas only, while a city parcel follows that city's rules². Check septic feasibility early because only 0.5% of mapped county soils are rated free of severe limitations for a conventional drain field¹¹. Review slope as well: 48.5% of county land is at a slope of 15% or less, so many parcels may bring grading or access complications¹¹. Confirm whether the building area lies in a FEMA Special Flood Hazard Area, because covered improvements need a floodplain permit and new or substantial improvements require an elevation certificate⁴¹. If rental income matters, unincorporated short-term rentals require a permit and are restricted by zoning, hosting arrangement and operating standards⁴⁶. Ask the water provider whether service is available; if a well is needed, budget for the county permit and inspections¹⁰. Finally, budget for property taxes: the effective rate is about 0.8%, and the median annual bill is about $6,903¹¹.