Walla Walla County, WA Environmental Rules: Flood Elevation Requirements (2026)

Walla Walla County adopted its flood damage prevention chapter, WWCC Chapter 18.12, to keep the county eligible for the National Flood Insurance Program in mapped special flood hazard areas along the Walla Walla and Touchet Rivers, Mill Creek, and the Snake and Columbia River shoreline near Burbank. WWCC 18.12.250(A) sets the core freeboard standard for houses: new construction and substantial improvement of any residential structure must have the lowest floor, including a basement, elevated to or above one foot above the base flood elevation shown on the community's Flood Insurance Rate Map.

Any fully enclosed area below that lowest floor that could flood is either prohibited or must be built to automatically equalize hydrostatic pressure, meeting minimum flood-vent criteria of at least two openings totaling one square inch of net free area per square foot of enclosed area, with the bottom of each opening no higher than one foot above grade, under WWCC 18.12.250(B). Nonresidential buildings get the same one-foot freeboard target under WWCC 18.12.260, but as an alternative can be floodproofed instead of elevated: the structure below that level must be watertight, with walls substantially impermeable to water and components able to resist hydrostatic and hydrodynamic loads, and a registered professional engineer or architect must certify that the standard is met.

Manufactured homes face their own one-foot freeboard and anchoring rules under WWCC 18.12.280 and 18.12.190. Where elevation data has not been generated, WWCC 18.12.230 still requires the permit reviewer to find construction reasonably safe from flooding, and warns that failing to elevate at least two feet above grade can raise flood insurance rates. A variance from the one-foot standard goes to the county hearing examiner under WWCC 18.12.150 through .170.