Florissant, MO Environmental Rules: Flood Elevation Requirements (2026)

040(B) sets Florissant's specific flood-hazard-reduction standards for the numbered and unnumbered A Zones and AE Zones where FEMA has published base flood elevation data. New construction or substantial improvement of any residential structure, including a manufactured home, must have its lowest floor, including any basement, elevated to one foot above the base flood elevation, the one-foot cushion commonly called freeboard. Commercial, industrial and other non-residential structures must meet the same one-foot freeboard, or, as an alternative, be floodproofed below that elevation so the structure is watertight, with walls substantially impermeable to water and structural components able to resist hydrostatic and hydrodynamic loads and buoyancy; a registered professional engineer or architect must certify that floodproofing meets the standard, and the certification goes to the City Engineer as floodplain administrator.

Enclosed areas below the lowest floor used only for parking, building access or storage must have flood openings, at least two openings with a net area of one square inch per square foot of enclosed area, with the bottom of each opening no more than one foot above grade, so floodwater can enter and exit automatically. Manufactured homes get the same one-foot freeboard above base flood elevation and must be secured to a permanent, anchored foundation system resistant to flotation, collapse and lateral movement. Critical facilities such as police and fire stations, hospitals and water and sewer plants are held to a stricter standard: they must be elevated above the five-hundred-year flood level or floodproofed to that higher elevation, with a professional engineer's certification.