Sonoma, CA Environmental Rules: Flood Elevation Requirements (2026)

Sonoma Municipal Code Chapter 14.25, the city's floodplain management regulations adopted by Ordinance 11-2022, defines 'base flood elevation' as the elevation of the base flood, including wave height, relative to the datum specified on the Flood Insurance Rate Map (FIRM) (SMC 14.25.480). Not every parcel in the City of Sonoma has a mapped base flood elevation. SMC 14.25.270 governs approximate Zone A areas, where flood hazard areas are delineated on the FIRM but no base flood elevation data have been provided. In that situation, the floodplain administrator may require the applicant to submit base flood elevation data prepared and sealed by a qualified California-licensed civil engineer; may obtain and provide data from a federal or state agency or another source, or require the applicant to do so; or, where no other data are available or the available data are inadequate, either require an engineer's study or specify that the base flood elevation is two feet above the highest adjacent grade at the site, provided there is no evidence that flood depths have been or may be greater than two feet.

Where a subdivision or other proposed development covers more than 50 lots or more than five acres and the FIRM lacks base flood elevation data, SMC 14.25.520 and 14.25.540 require those elevations to be established under SMC 14.25.270(B) before the project can be approved. Once a base flood elevation is established, related provisions in the same chapter tie construction elevation to it: detached garages and accessory storage structures under 600 square feet may sit below the base flood elevation only if their mechanical, plumbing and electrical systems are elevated to or above it (SMC 14.25.500), and manufactured homes outside an existing park or subdivision must have their lowest floor elevated to or above the base flood elevation (SMC 14.25.620).

General buildings and structures within the scope of the building code are instead governed by the California Building Standards Code as locally adopted and amended by the City of Sonoma (SMC 14.25.490), so a freeboard figure for ordinary buildings sits in the adopted building code, not in this chapter's text.