Jefferson County, MO Environmental Rules: Flood Elevation Requirements (2026)

060(A)(2). 060(B)(1)(a) requires that new construction or substantial improvement of any residential structure, including manufactured homes, have its lowest floor, including any basement, elevated to three feet above base flood elevation, three feet more than the FEMA-mapped base flood elevation itself, a freeboard buffer built into the local ordinance. 050(C)(7). 060(B)(1)(b) allows the same three-foot-above-base-flood-elevation standard, or, as an alternative, dry floodproofing so the structure is watertight below the base flood elevation with walls substantially impermeable to water and structural components able to resist hydrostatic and hydrodynamic loads and buoyancy; a Missouri registered professional engineer or architect must certify that standard is met.

060(B)(1)(c) further requires enclosures below the lowest floor used for parking, building access or storage to have flood openings equalizing hydrostatic pressure, at least two openings totaling one square inch of net area per square foot of enclosed area, with the bottom of each opening no higher than one foot above grade.