Antioch, CA Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard, Zone AE/AH
- 12 inches above base flood elevation
- Zone AO elevation
- FIRM depth number, or 2 ft minimum
- Nonresidential option
- Floodproofing allowed instead of elevation
- Certification required
- Registered engineer, surveyor, or Building Inspector
- Vent requirement
- 1 sq in per sq ft of enclosed area
- Violation penalty
- Misdemeanor under AMC § 9-4.2004(C)
Summary
New construction and substantial improvements in Antioch's Zone AE and AH flood areas must have the lowest floor, including any basement, built at least 12 inches above the base flood elevation shown on the FIRM. Nonresidential buildings can floodproof instead. A registered engineer, surveyor, or the Building Inspector must certify the elevation to the Floodplain Administrator.
New construction and the substantial improvement of any structure in Zone AE or Zone AH shall have the lowest floor, including the basement, elevated at least 12 inches above the base flood elevation. The depth number specified on the FIRM shall be used to determine the elevation of the base flood. Nonresidential structures may meet the standards set forth in subdivision (c) of this subdivision. Upon the completion of the structure, the elevation of the lowest floor, including the basement, shall be certified by a registered professional engineer or surveyor or verified by the Building Inspector to be properly elevated. Such certification or verification shall be provided to the Floodplain Administrator.
Full Breakdown
Article 20's construction standards set actual freeboard above the federal base flood elevation (BFE), not just compliance with it. 2007(B)(3)(a), new construction and substantial improvements in Zone AE or Zone AH must have the lowest floor, including any basement, elevated at least 12 inches above the BFE. 2007(B)(3)(b) instead requires the lowest floor to sit above the highest adjacent grade by at least the depth number shown on the FIRM, or two feet if none is shown. 2007(B)(3)(c): the building must be watertight below the base flood level, with walls and utilities able to resist hydrostatic and hydrodynamic loads, certified by a registered engineer or architect. 2005(C)(4). 2007(B)(3)(d). 2007(B)(4).
Violations & Fines
Occupying or completing new construction in Zone AE, AH, or AO without the certified 12-inch freeboard, the required AO grade elevation, or approved floodproofing violates Article 20 and is a misdemeanor under § 9-4.2004(C), citable under the general penalty schedule at §§ 1-2.01 et seq. The Floodplain Administrator can withhold final building sign-off until a professional elevation certificate is filed, and the Council retains separate authority to order noncompliant work corrected.
Frequently Asked Questions
How high above the flood elevation must I build in Antioch?
Can I floodproof instead of raising a nonresidential building?
Who certifies the finished elevation?
Sources & Official References
Other rules in Antioch
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Flood Elevation Requirements in Nearby Cities
How other cities in Contra Costa County handle flood elevation requirements.