Building permits, zoning and septic rules in Trinity County, California

Yes: Trinity County requires a building permit for new construction, and work may not start until the Building Division issues the required approval and permit¹. Trinity County has adopted the California Building Code in Title 24, Part 2, and incorporates newer editions and amendments by reference⁷. The current code cycle matters for timing: the 2025 California Building Standards Code applies to permit applications filed on or after January 1, 2026⁸. A narrower path exists for a qualifying agricultural building used for implements, hay, grain, poultry, livestock or horticultural products: submit a letter of intent for Building Division review⁹. That agricultural exemption does not cover human habitation, public use, retail processing, plumbing or electrical work, and the structure must still comply with its zoning and any overlay district⁹.

Trinity County's Building Division sits inside the Community Development Department, and Building and Planning share the phone number 530-623-1351; Planning is extension 2^10,11. The Planning Division is at 530 Main Street, Weaverville, California 96093¹¹. A complete building permit application needs a project description, APN, site and building plans, square footage, setbacks and maximum height; an incomplete application is returned and may produce added resubmittal fees¹². Building, Planning and Environmental Health fees vary with the project, so ask Planning for an estimate of the applicable charges and the county-calculated plan-review and zoning deposit¹³. An owner-builder must personally complete and sign the county acknowledgment before the building permit can issue and remains legally and financially responsible for the work¹. The owner-builder exemption concerns contractor licensing, not required building permits or inspections³.

Yes: Trinity County administers zoning under Title 17, and the parcel's district controls allowed uses, setbacks, height, density, temporary uses and accessory structures². The county publishes a zoning matrix, but it is only an early-planning tool and does not determine compatibility, timing, cost or approval; make a project-specific appointment with Planning¹³. Trinity County does not impose a general minimum dwelling-unit size beyond state health and safety standards, although building-code, sanitation, septic, district and special-use requirements still apply⁷. Lot size is a separate question: in the Unclassified district, the minimum is one recorded parcel of at least 5 acres¹⁴. Creating or adjusting parcels requires the applicable subdivision-map process, with legal-access, drainage, water and sewage-disposal information; proposed parcels using new sewage systems need 2 percolation-test results per parcel². In the Unclassified district, buildings need yards of at least 20 feet in front, 10 feet on each side and 20 feet at the rear, structures may cover no more than 25% of the lot, and building height is capped at 40 feet¹⁴. The county says its zoning code update has been extended into 2027, so confirm the operative rules for the parcel with Planning¹³.

Trinity County Environmental Health processes septic permits, and a permit is required before you build wherever a project needs onsite wastewater disposal². Properties inside the Weaverville and Hayfork sewer districts must connect to district sewer, while rural property outside those districts and Lewiston's private sewer service generally depends on a septic tank and leach lines⁷. Only about 1.1% of Trinity County's mapped soils are free of severe limitations for a conventional septic drain field, making a parcel-specific site evaluation especially important before purchase¹⁵. Environmental Health must verify an installed system at final inspection before issuing a Notice of Final Inspection, and the county recommends pumping a tank every 3 to 5 years¹⁶. The same office handles water-well permits: a well, monitor or soil-boring permit costs $449, remains valid for one year from approval, and must be issued before drilling starts⁶. Reach Environmental Health at 530-623-1459 or environmentalhealth@trinitycounty.org, Monday through Thursday, 8 a.m. to 2 p.m¹⁷..

Trinity County adopted a Movable Tiny Homes ordinance in 2025 that lets a tiny home be permitted in any zoning district that already allows a single-family dwelling by right, including the Unclassified, Agricultural, Agricultural Preserve, Agricultural Forest and Rural Residential districts⁴. That tiny home has to stay one story, except for sleeping lofts, and no larger than 400 square feet, be licensed and registered with the DMV or the state Department of Housing and Community Development, get a zoning clearance, and have water and sewage disposal approved by Environmental Health and connected before final inspection^4,17.

For a standard RV, California's default is that an RV is not meant for permanent dwelling occupancy and generally may only be occupied in a mobilehome park or a special occupancy park unless a local ordinance says otherwise⁵. Trinity County does allow one local exception: temporary occupancy of an RV during construction of a single-family dwelling, regardless of parcel size, with a director's use permit¹⁸. A valid building permit for the house must be in effect, Environmental Health must permit the sewage disposal and the RV must be connected to it, and the use permit lasts 1 year unless renewed¹⁸. Once the house is cleared for occupancy, the RV must be disconnected from all utilities and not lived in¹⁸. A manufactured home is a separate path: it can be occupied inside or outside a mobilehome park if it meets Title 25's minimum 8-foot width and 320-square-foot floor area and goes through Mobilehome Parks Act approval⁵.

1. Call the Community Development Department at 530-623-1351 to confirm the parcel's zoning district and application requirements^2,10.
2. Determine wastewater service early: properties in the Weaverville and Hayfork sewer districts must connect, while most rural sites need Environmental Health septic review^2,7.
3. If you need a well, apply through Environmental Health; a well, monitor or soil-boring permit costs $449, is valid for one year and must precede drilling⁶.
4. For a driveway affecting county right-of-way, obtain the county encroachment permit before work and budget the listed $150 driveway fee; Caltrans handles access from a state highway^19,20.
5. If the site is in an FH or FHO zone, secure a Floodplain Development Permit before construction or any other county entitlement; a new or substantially improved building in the Special Flood Hazard Area also needs an Elevation Certificate^21,22.
6. Submit the project description, APN, site and building plans, setbacks, square footage and maximum height; incomplete applications are returned and can incur added resubmittal fees¹².
7. Complete the required inspections and obtain a certificate of occupancy after the final inspection confirms compliance¹.

Soils: only about 1.1% of Trinity County's mapped soils are free of severe limitations for a conventional septic drain field, so have Environmental Health or a licensed designer assess the parcel before closing^15,17. Terrain: just 8.9% of the county is at 15% slope or less, and roughly 87% is wooded, so usable building ground may demand substantial site work¹⁵. Ownership: about 78% of Trinity County is federal land, so verify private ownership and boundaries carefully¹⁵. Access: a new or replacement driveway affecting county right-of-way needs a county encroachment permit before work, while state-highway access goes through Caltrans^19,20. Flood: construction or development in FH or FHO zones requires a Floodplain Development Permit, and every new or substantially improved building in a Special Flood Hazard Area needs an Elevation Certificate^21,22. Climate and cost: Trinity County averages about 57.1 inches of annual precipitation, with roughly 35% of years in severe drought; typical annual home insurance is near $2,094, and the median property-tax bill is about $1,772 at an effective rate near 0.5%¹⁵.