Sammamish, WA Environmental Rules: Flood Elevation Requirements (2026)

130(2). For residential construction in an AE or A1-30 zone, or another A-zoned area where the BFE can be reasonably obtained, the lowest floor, including any basement, must sit at least one foot above the base flood elevation, and mechanical equipment and utilities must be waterproofed or elevated to that same one-foot minimum above the BFE. A crawlspace exception is available if the interior grade below the BFE is no more than two feet below the lowest adjacent exterior grade, the crawlspace height does not exceed four feet, and an adequate drainage system removes floodwater from the space.

Fully enclosed areas below the lowest floor are otherwise prohibited unless engineered, or fitted, with a minimum of two openings totaling at least one square inch of net area per square foot of enclosed space, with opening bottoms no higher than one foot above grade, to let floodwater automatically enter and exit. 160(1)(d) instead requires the lowest floor to sit at least two feet above the highest adjacent grade. 160(3).