National City, CA Environmental Rules: Flood Elevation Requirements (2026)

The flood rules sit in § 18.29.070 of the National City Land Use Code (Title 18), the overlay chapter that creates the Floodway (FW) and Floodway Fringe (FF-1 through FF-4) zones. The chapter adopts by reference the Federal Emergency Management Agency flood insurance study for National City dated August 4, 1988, with its flood insurance rate maps, floodway maps and all later amendments. Those documents are kept at the floodplain administrator's office at 1243 National City Boulevard, and the city engineer holds the floodplain administrator job.

The elevation rule applies to new construction and substantial improvement. A substantial improvement is work whose cost equals or exceeds fifty percent of the structure's market value before the work starts, and substantial damage is measured the same way. Once the structure is finished, a registered professional civil engineer or surveyor certifies the lowest-floor elevation and the certification goes to the floodplain administrator.

Nonresidential buildings have a second route. They can meet the same elevation rule, or be completely flood-proofed so the walls are watertight and substantially impermeable, with structural components that resist hydrostatic and hydrodynamic loads and a civil engineer's certification. Fully enclosed areas below the lowest floor that serve only parking, building access or storage must either carry an engineer's certification or have at least two openings totaling not less than one square inch for every square foot of enclosed area, with the bottom of every opening no higher than one foot above adjacent natural grade.

In coastal high hazard zones (V, V1-30 and VE) the bottom of the lowest horizontal structural member must sit at or above the base flood level, on anchored pilings or columns. A development permit from the floodplain administrator is required before any building, grading or conditional use permit issues in a mapped area. Variances go to the planning commission, and anyone granted a variance to build below the base flood level receives written notice that flood insurance premium rates will rise. That notice is recorded with the San Diego County Recorder.