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

Section 15.50.150(C) requires new or substantially improved residential construction to have its lowest floor, including basement, elevated to or above the base flood elevation in an A zone or any other zone, or in an AO zone elevated above the highest adjacent grade to the FIRM's depth number or at least two feet if no depth number is specified. Once built, a registered professional engineer or surveyor must certify the lowest-floor elevation, and the community building inspector must verify it, with both submitted to the floodplain administrator (§ 15.50.150C1).

Nonresidential construction may floodproof instead of elevate, provided the structure is watertight below the required elevation with walls substantially impermeable to water, has components able to resist hydrostatic and hydrodynamic loads, and is certified by a registered engineer or architect (§ 15.50.150C2). Any fully enclosed area below the lowest floor used only for parking, access, or storage must equalize hydrostatic forces, either through engineer/architect certification or a minimum of two openings totaling at least one square inch of net area per square foot of enclosed area, with opening bottoms no higher than one foot above grade (§ 15.50.150C3).

Manufactured homes are additionally bound by § 15.50.190. When base flood elevation data has not been set for a site under § 15.50.060, the floodplain administrator must obtain, review, and use the best available federal, state, or other data, and submit it to the city council for adoption (§ 15.50.130B).