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

60 of the Orange Municipal Code, adopted under the authority of Government Code Sections 65302, 65561 and 65800, governs construction within the city's mapped flood hazard areas. 160(C) sets the core elevation standard: all new construction, substantial improvements and substantially damaged structures, including manufactured homes, must be elevated at minimum to the base flood elevation shown on the effective Flood Insurance Rate Map, plus one foot of freeboard. For residential construction specifically, the lowest floor including any basement must clear the highest adjacent grade by more than the depth number printed on the FIRM, plus at least one foot, or by at least three feet if no depth number is shown, when the parcel sits in an AO Zone; in an A Zone the lowest floor must clear the base flood elevation by at least one foot as determined by the City; and in every other zone the same one-foot-above-base-flood-elevation floor applies.

A registered professional engineer or surveyor must certify the finished elevation, or the City's building inspector must verify it, with that certification filed with the Floodplain Administrator. Nonresidential buildings may instead be floodproofed watertight below that same elevation, with structural components engineered to resist hydrostatic and hydrodynamic loads, again certified by a registered engineer or architect. Enclosed areas below the lowest floor used only for parking, building access or storage must include flood vents: at least two openings on different walls providing not less than one square inch of net area per square foot of enclosed area, with openings no higher than one foot above grade. 230, generally limited to lots of a half-acre or less.