Fountain Valley, CA Environmental Rules: Flood Elevation Requirements (2026)

Section 21.14.040(p)(3)(A) sets the one-foot freeboard: new construction and substantial improvement of a residential structure needs its lowest floor, including basement, one foot above the base flood elevation, or elevated in accordance with the current California Building Code. The base flood is the flood with a one percent chance of being equaled or exceeded in any year. After completion, a registered civil engineer or surveyor certifies the lowest floor elevation and gives it to the floodplain administrator. The code's 'lowest floor' definition excludes an unfinished or flood-resistant enclosure used solely for parking, building access or storage, unless it is a basement.

In zone AO the lowest floor must be at least as high as the FIRM depth number in feet above the highest adjacent grade, plus a foot (the code prints 'plus on foot'), or three feet if no depth number is specified. A registered civil engineer certifies that elevation.

Nonresidential buildings can meet the elevation rules or be flood proofed below the base flood level so the walls are watertight, with a licensed civil engineer or surveyor certifying it under § 21.14.040(p)(3)(C). Fully enclosed areas below the lowest floor need flood openings totaling at least one square inch per square foot, with the bottom of each opening no higher than one foot above grade.

Manufactured homes in parks sit on pads or pilings so the lowest floor is one foot above base flood level or per the California Building Code, whichever is higher (§ 21.14.040(s)(2)(B)). Subdivision plans must identify the base flood elevation, and pad elevations for filled sites are certified. Where the FIRM lacks base flood elevation data, the administrator uses other federal, state or other data. A variance for a lowest floor below the base flood elevation comes with written notice that flood insurance will cost more.