Building in a flood zone in Costa Mesa: the local rules

Each rule below links to the section of the Costa Mesa Municipal Code it was read from, with the code text one click away (checked October 2026). General information, not legal advice.

What Costa Mesa's code says

Costa Mesa code What Costa Mesa's code adds
Floodplain permit	A permit is required for all proposed development. Applies: Applies in Zone A on the city's flood insurance rate map (FIRM). § 13-82 · code text Require permits for all proposed development within Zone A on the city's FIRM;
Building in a floodway	No permanent buildings except for flood drainage, utilities and roads; no encroachments that raise flood levels or block flood flows. Applies: Applies in floodway areas. § 13-80 · code text Any permanent structures or buildings excepting those necessary for conveyance of flood and drainage waters and for transit of public utilities and roads. Conditional uses may be approved only if they do not reduce carrying capacity or raise flood heights or floodwater speed. Applies: Applies to other uses considered for approval as a conditional use in the floodway. § 13-80 · code text The proposed project, alone or in combination with any existing developments, will not endanger public safety, will not restrict the carrying capacity of the regulatory floodway, will not increase flood heights and will not increase the velocity of floodwaters.
Height of the lowest floor	The lowest floor, including any basement, must be at or above the base flood elevation. Applies: New construction and substantial improvements in areas of special flood hazard. § 13-82 · code text New construction and substantial improvement of any structure shall have the lowest floor, including basement, elevated to or above the base flood elevation. The lowest floor must be at least 2 feet above the highest adjacent grade. Applies: New construction and substantial improvements in Zone AO and Zone AH where the flood map (FIRM) shows no depth number. § 13-82 · code text If there is no depth number on the FIRM, the lowest floor, including basement, shall be elevated at least two feet above the highest adjacent grade.

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Frequently asked questions

What are the rules for building in a Costa Mesa flood zone?

Costa Mesa's code: A permit is required for all proposed development. (Applies in Zone A on the city's flood insurance rate map (FIRM).) (§ 13-82); The lowest floor, including any basement, must be at or above the base flood elevation. (New construction and substantial improvements in areas of special flood hazard.) (§ 13-82).

Building in a flood zone in Costa Mesa

What Costa Mesa's code says

Who this affects

Frequently asked questions

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