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

Section 425.160, Specific Standards, adopted by Ordinance No. 1468 on January 21, 2010, applies once base flood elevation data exists for a numbered or unnumbered A Zone or AE Zone under Section 425.150(B). For residential construction, including manufactured homes, the lowest floor, including any basement, must be elevated to one foot above the base flood elevation, a freeboard margin above the minimum FEMA requires. Non-residential structures, including commercial and industrial buildings, face the same one-foot elevation standard, or may instead be floodproofed so the structure below that elevation is watertight, with walls substantially impermeable to water and components able to resist hydrostatic and hydrodynamic loads; a registered professional engineer or architect must certify that floodproofing meets the standard, and that certification goes to the Floodplain Administrator under Section 425.130(9).

For any new construction with fully enclosed areas below the lowest floor used for parking, building access or storage, Section 425.160 requires automatic flood-vent openings unless an engineer certifies an alternative design: a minimum of two openings with at least one square inch of net area for every square foot of enclosed area subject to flooding, with the bottom of each opening no higher than one foot above grade. Section 425.170 applies a parallel one-foot elevation standard to manufactured homes placed in these zones, requiring anchoring to resist flotation, collapse or lateral movement.

The Building Inspector, as Floodplain Administrator, verifies and records the actual elevation of the lowest floor of every new or substantially improved structure under Section 425.130.