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

190 sets the specific elevation standards that apply once base flood elevation (BFE) data exists for a site. Residential structures in AE, A1-30, or other A zones must have the finished floor of the lowest level, including any basement, elevated two feet or more above the BFE, with mechanical and utility equipment waterproofed or raised at least one foot above the BFE. Where no BFE data can be reasonably obtained, the lowest floor must still sit at least two feet above the highest adjacent grade.

Nonresidential buildings must meet the same two-foot elevation, or the ASCE 24 standard if it is higher, or be dry floodproofed to two feet above the base flood level with certification from a licensed engineer or architect. Enclosed areas below the lowest floor need flood vents sized at one square inch of net opening per square foot of enclosed area, with openings no higher than one foot above grade, or an engineer-certified equivalent design. Manufactured homes must sit on permanent foundations with the lowest floor two feet or more above the BFE, footings at least twelve inches below the pre-development grade, and be securely anchored against flotation and lateral movement. Shallow-flooding AO zones use the FIRM's depth number plus two feet instead of a fixed BFE.