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

In AE and A1-30 zones, or other A-zoned areas where the base flood elevation has been determined, RMC § 22.16.050(B)(1)(a) requires new and substantially improved residential structures to have the lowest floor, including any basement, elevated one foot or more above the BFE, with mechanical equipment and utilities waterproofed or raised the same one foot. Where a residential structure sits in an unnumbered A zone with no BFE available, RMC § 22.16.050(B)(1)(b) instead requires the lowest floor to sit at least two feet above the highest adjacent grade.

Commercial, industrial and other nonresidential buildings face the same one-foot freeboard above the BFE, or the elevation required by ASCE 24 if that is greater, under RMC § 22.16.050(B)(3)(a)(i); nonresidential buildings may flood-proof instead, but only with certification from a registered professional engineer or architect. Enclosed areas below the lowest floor that could flood are barred unless designed with at least two openings, totaling one square inch of net area per square foot of enclosed space, with the bottom of every opening no higher than one foot above grade.

Applicants for a development permit must submit pre- and post-construction elevation surveys tied to NAVD-88 datum under RMC § 22.16.040(A)(2)(a), and the development services director, acting as floodplain administrator, keeps those elevation certificates on file. Building below the required freeboard is a civil violation under RMC § 22.16.030(D), punishable under Chapter 1.30 RMC.