Mendocino County

Mendocino County Planning and Building Services issues ADU permits for unincorporated parcels (the bulk of the county outside the four incorporated cities). The unincorporated coast (Westport, Albion, Little River, Mendocino village CDP, Elk, Manchester, Anchor Bay, Gualala) sits inside the certified Local Coastal Program zone and requires a Coastal Development Permit (CDP) on top of the standard ADU permit unless the project qualifies under a categorical exclusion. Inland unincorporated areas (Redwood Valley, Calpella, Talmage, Hopland, Boonville, Philo, Yorkville, Laytonville, Covelo, Leggett) follow the standard state-preempted 60-day ministerial path. Practical permitting frictions: very high fire severity zones across most interior ridge country, septic/well dependence outside the small Russian River Valley sewer service areas, steep-slope grading review on coastal terrace bluffs and inland mountains, redwood / oak woodland habitat considerations, sensitive habitat overlays in coastal LCP review, and commercial cannabis ordinance interactions on cultivation-licensed parcels.

Process overview: Inland unincorporated parcels: standard ministerial 60-day review per Sec. 65852.2(b) for compliant ADU applications. Coastal zone unincorporated parcels: state ministerial 60-day review applies AND a Coastal Development Permit must be issued either under a categorical exclusion in the certified LCP or by the county acting as the LCP authority (with possible Coastal Commission appeal). Coastal CDP review can extend total timelines to 90-180 days for non-categorically-excluded projects. Parcels in very high fire severity zones require Chapter 7A ignition-resistant construction. Septic/well parcels require Environmental Health review (well permit, percolation test, septic system design). Cannabis-licensed parcels require coordination with the Cannabis Program to confirm ADU siting does not conflict with cultivation setbacks or licensed canopy area.

Impact fees: SB 13 fee waivers apply to ADUs under 750 sqft (no impact fees). Larger ADUs are charged proportionally to the primary dwelling. School district fees apply to ADUs over 500 sqft per Education Code Sec. 17620.

The Mendocino County Assessor's Office maintains parcel-level assessment records for the entire county. ADU additions on unincorporated parcels are captured as improvements via shared permit data with Planning and Building Services. 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 assessor's parcel-lookup portal (Megabyte / Parcel Quest) is publicly accessible. Williamson Act parcels (agricultural preserve contracts under Cal. Gov't Code Sec. 51200 et seq.) cover much of Anderson Valley and Redwood Valley wine-grape and ranching parcels.

Assessment policy: ADU improvement value is added on the next regular revaluation cycle following completion, not at permit issuance. Per Prop 13, the ADU's value is taxed at 1 percent of fair market value at completion (plus voter-approved local rates), while the existing structure remains at its base-year value plus 2 percent annual cap. Williamson Act parcels in Anderson Valley (wine-grape AVA) and Redwood Valley benefit from agricultural use-value assessment; ADUs on Williamson Act parcels are permitted but the parcel's overall use must remain consistent with the agricultural preserve contract.

Mendocino County overlays of consequence: California Coastal Zone (LCP-certified) covers the entire coastal strip from the Sonoma County line north to Humboldt County line; CAL FIRE Very High Fire Hazard Severity Zone (FHSZ) covers most of the interior ridge country; California WUI Chapter 7A applies in the FHSZ; FEMA SFHA along the Russian River, Eel River, Big River, and Navarro River drainages; commercial cannabis cultivation overlay (Mendocino County Code Title 10A.17) on licensed parcels; Anderson Valley AVA (American Viticultural Area) and Mendocino AVA wine-grape parcels with significant Williamson Act coverage; multiple federal Wild and Scenic River segments (Eel River and tributaries); coastal redwood and old-growth habitat overlays; and TPZ (Timber Production Zone) parcels under Cal. Gov't Code Sec. 51100 et seq. covering large industrial timberland inholdings.

• California Coastal Zone - Mendocino County certified Local Coastal Program
• CAL FIRE State Responsibility Area / Very High FHSZ
• FEMA SFHA - Russian, Eel, Navarro, Big River drainages
• Mendocino County Commercial Cannabis Cultivation Ordinance
• Williamson Act / TPZ - Anderson Valley AVA and Mendocino AVA wine-grape and timber parcels
• California Scenic Highway System - Highway 1 (Pacific Coast Highway) and Highway 128