Trinity County

Trinity County Department of Planning issues ADU permits for the entire county (since there are no incorporated cities) including Weaverville, Hayfork, Lewiston, Junction City, Hyampom, Burnt Ranch, Mad River / Ruth Lake, Trinity Center, Coffee Creek, Salyer, Big Bar, and Helena. Practical permitting frictions: extensive CAL FIRE State Responsibility Area covering essentially the entire county; significant Very High FHSZ across the bulk of the county; the county has been heavily affected by recent megafires (2017 Helena Fire, 2018 Carr Fire ~230,000 acres in Shasta / Trinity, 2020 August Complex ~1,032,000 acres including substantial southern Trinity); the Shasta-Trinity National Forest and Six Rivers National Forest covering ~75-78% of the county area; the Trinity Alps Wilderness Area in the northeastern county (~525,000 acres); the Trinity River Wild and Scenic River corridor; the Trinity River Restoration Program governance affecting parcels downstream of Lewiston Dam; FEMA SFHA along the Trinity River, Hayfork Creek, Coffee Creek, Mad River, and the New River; the Hoopa Valley Tribe (a federally-recognized tribe whose reservation sits on the Trinity / Humboldt County line and whose ancestral territory includes western Trinity); the Yurok Tribe ancestral territory in the western county; the Wintu / Wintun ancestral territory in the eastern county; high-elevation snow-load and freeze-depth structural design (Trinity Alps elevations exceed 9,000 ft; the Weaverville basin sits at ~2,000 ft but the surrounding ridgelines reach 5,000-7,000 ft); rural well-water / septic on essentially all parcels; severe single-egress evacuation constraints in the Trinity River canyon corridor (Hwy 299) and the Hayfork-Forest Glen corridor (Hwy 36); and post-fire insurance market dislocation that has materially affected lender willingness to finance new ADU construction.

Process overview: Standard ministerial 60-day review per Sec. 65852.2(b) for compliant ADU applications. The very small staff means appointment scheduling is required and the practical timeline is often longer than the 60-day statutory floor though state-law deemed-approval provisions apply. Within Very High FHSZ (essentially the entire county), Chapter 7A ignition-resistant construction, PRC 4291 defensible space, and CAL FIRE driveway/turnaround review apply. AB 38 home-hardening provisions apply to post-fire rebuilds (declared disaster areas DR-4382 Carr, DR-4569 August Complex, DR-4308 Helena, plus several earlier declarations). Wildfire evacuation-route adequacy is acute in the Trinity River canyon corridor and the Hayfork-Forest Glen corridor; CAL FIRE driveway requirements are rigorously enforced. High-elevation snow-load and freeze-depth structural design is a baseline requirement on parcels above ~3,500 ft elevation. Septic-suitability evaluation by Trinity County Environmental Health is required on essentially all parcels. Federal land (Shasta-Trinity NF, Six Rivers NF, Trinity Alps Wilderness) is exempt from county zoning; private inholdings carry severe access, fire-protection burden, and seasonal road closure constraints. Trinity River Wild and Scenic corridor parcels carry NPS / USFS scenic and riparian review. Tribal-consultation requirements (Hoopa Valley, Yurok, Wintu, Tsnungwe, Nor Rel Muk Wintu) apply to CEQA-triggered projects.

Impact fees: SB 13 fee waivers apply to ADUs under 750 sqft (no impact fees). For ADUs 750+ sqft, county impact fees are calculated proportionally. CAL FIRE driveway/defensible-space inspection fees apply on essentially all parcels. Septic permits required (typically $1,500-$5,000 depending on system type and remoteness; some parcels require engineered systems). School-district fees per Education Code Sec. 17620 on ADUs over 500 sqft (Trinity Center ESD, Lewiston ESD, Weaverville ESD, Burnt Ranch ESD, Junction City ESD, Hayfork USD, Mountain Valley USD, Trinity Alps USD, Cox Bar ESD, Big Bar ESD by sub-area; Trinity is one of the most fragmented small-school-district counties in California). Post-fire reconstruction permits in declared disaster areas may receive expedited processing.

The Trinity County Assessor / Recorder maintains parcel-level assessment records for the entire county. ADU additions are captured as improvements via shared permit data with Planning. California Proposition 13 caps base-year valuation increases at 2 percent per year on the existing structure; new improvement value (the ADU) is added as a separate line item assessed at fair market value at completion. The bulk of the county is federal land (Shasta-Trinity NF, Six Rivers NF, Trinity Alps Wilderness, BLM) which is exempt; private parcels constitute roughly 22-25% of county area but a smaller fraction of total county assessed valuation. Williamson Act parcels exist in the limited agricultural valleys (Hayfork Valley, Hyampom Valley, Trinity River bottomland) carrying agricultural use-value assessment. Post-disaster Prop 50 / Prop 19 base-year-value transfer is available to property owners with structures destroyed in declared disasters; this applies broadly across the county post-Carr / August Complex / Helena fires.

Assessment policy: ADU improvement value is added on the next regular revaluation cycle following completion. Per Prop 13, the ADU's value is taxed at 1 percent of fair market value at completion (plus voter-approved local rates). Conversion ADUs (within existing structure) typically generate smaller incremental assessments than detached new construction. Williamson Act parcels: ADU addition compatible with continuing agricultural use does not trigger non-renewal; non-compatible additions trigger 9-year non-renewal phase-out. Post-disaster Prop 50 / Prop 19 base-year-value transfer is available; this is materially relevant given Trinity's recent fire history.

Trinity County overlays of consequence: (1) Shasta-Trinity National Forest, Six Rivers National Forest, Trinity Alps Wilderness, and BLM federal land covering ~75-78% of the county; (2) the Trinity River federally-designated Wild and Scenic River corridor; (3) CAL FIRE SRA Very High FHSZ across essentially the entire county; (4) the post-2017 Helena / 2018 Carr / 2020 August Complex burn scar covering substantial portions of the county; (5) the Trinity River Restoration Program governance downstream of Lewiston Dam; (6) FEMA SFHA along the Trinity River and tributaries; (7) tribal-consultation overlays for Hoopa Valley Tribe, Yurok Tribe, Wintu, Tsnungwe, Nor Rel Muk Wintu, and other ancestral peoples; (8) high-elevation snow-load and freeze-depth structural overlays; and (9) the Trinity Lake / Lewiston Lake recreation-resource overlay administered by the USBR / USFS.

• Shasta-Trinity National Forest / Six Rivers National Forest / Trinity Alps Wilderness / BLM
• Trinity River federally-designated Wild and Scenic River corridor
• CAL FIRE State Responsibility Area / Trinity Very High FHSZ - Carr / August Complex / Helena burn scar
• Post-2017 Helena / 2018 Carr / 2020 August Complex / 2022 McKinney recovery zone
• FEMA SFHA - Trinity River, Hayfork Creek, Coffee Creek, Mad River, New River
• Trinity River Restoration Program (TRRP) governance
• Hoopa Valley Tribe / Yurok Tribe / Wintu / Tsnungwe / Nor Rel Muk Wintu ancestral-territory consultation
• High-elevation snow-load / freeze-depth structural overlay
• Trinity Lake / Lewiston Lake recreation-resource overlay (USBR / Central Valley Project)