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

080 sets the county's freeboard standard for the unincorporated area: in any zone where FEMA has provided base flood elevation data, new construction and substantial improvements to residential structures must have the lowest floor, including any basement, elevated to one foot or more above base flood elevation. 080(c) requires at least two openings totaling one square inch of net area per square foot of enclosed space, with the lowest opening no higher than one foot above grade. 080(b): elevate the lowest floor one foot above base flood elevation like a residence, or floodproof the structure watertight to that same one-foot mark, with a registered professional engineer certifying the design and utility systems built to resist hydrostatic and hydrodynamic loads.

Floodproofed nonresidential buildings are warned their flood insurance will still be rated one foot below the floodproofed level. 080(e). 070(f) falls back to a two-foot standard: in unnumbered A zones construction is deemed reasonably safe from flooding only if the lowest floor sits at least two feet above the highest adjacent grade, and the county warns that falling short of that two-foot mark can trigger higher federal flood insurance premiums. 030(f) before work begins.