Sonoma County, CA Environmental Rules: Flood Zones (2026)

Chapter 7B of the Sonoma County Code (Flood Damage Prevention) was adopted when the County voluntarily joined the National Flood Insurance Program (NFIP) and is enforced by Permit Sonoma's Engineering & Construction Division. The zoning code overlays F1 (Floodway) and F2 (Floodplain) match the FEMA Special Flood Hazard Area (SFHA) on the most recent Flood Insurance Rate Maps (FIRM). In the F2 / SFHA zone, the lowest floor of any new residential structure, including basements and enclosed utility areas, must be elevated at least 1 foot above the Base Flood Elevation (BFE) - this 1-foot 'freeboard' exceeds the federal NFIP minimum of 0 feet. Non-residential structures may be either elevated or dry-flood-proofed to the same elevation. In the F1 floodway, no new construction, substantial improvement, or fill that would increase BFE may occur. 'Substantial improvement' is any reconstruction, addition, or repair whose cost equals or exceeds 50% of the structure's market value - triggering full Chapter 7B compliance for the entire structure (Technical Bulletin B-47). Manufactured homes must be on a permanent foundation elevated to or above the BFE plus freeboard, with anchoring against flotation and lateral movement. The FEMA Russian River Watershed FIRMs were finalized July 31, 2024 (effective for permitting and insurance rating in 2025-2026). Sonoma County participates in the NFIP Community Rating System (CRS), giving residents discounts on flood-insurance premiums. Elevation Certificates are required for all new construction in the SFHA.