Federal Way, WA Environmental Rules: Flood Elevation Requirements (2026)

140(1)(a) sets the city's freeboard standard: new construction and substantial improvement of any residential structure in zone AE must have the lowest floor, including the basement, elevated one foot or more above the base flood elevation (BFE). Enclosed areas below that elevated floor are banned outright unless used solely for parking, building access, or storage, and even then they must be engineered to automatically equalize hydrostatic pressure. 140(1)(b) requires a minimum of two openings with at least 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, or certification from a registered professional engineer or architect that an equivalent design meets the standard.

The code specifically warns that standard IBC/IRC foundation vents built outside the floodplain do not satisfy this rule and are often permitted in error, and that a partially ventilated crawlspace can trigger a 20 to 25 percent surcharge on the annual flood insurance premium. 140(3), or may instead be floodproofed watertight to that elevation with structural components certified to resist hydrostatic and hydrodynamic loads. 140(5). 040 to include schools, hospitals, and emergency response installations, face a stricter three-foot-above-BFE standard when sited in the special flood hazard area. 080. Upon completion, a registered professional engineer or surveyor must certify to the director that the lowest-floor elevation requirement was actually met.