Washington County, WI Environmental Rules: Flood Elevation Requirements (2026)

§ 275-2 defines flood protection elevation as an elevation that corresponds to a point 2.0 feet above the regional flood, the county's freeboard standard. § 275-16C(1)(a) applies that definition to new construction in the Floodfringe District: any new residential structure, including a manufactured home, and any substantial improvement of a residential structure, must have its lowest floor elevated to or above the flood protection elevation on fill, with that fill extending at least one foot above the regional flood elevation and reaching at least 15 feet beyond the structure's limits. § 275-16C(1)(b) allows an exception for a basement or crawlspace floor placed at the plain regional flood elevation, without the 2-foot freeboard, but only if the below-grade portion is designed watertight, with walls substantially impermeable to water and structural components able to resist hydrostatic and hydrodynamic loads; no floor of any kind may sit below the regional flood elevation itself.

The same freeboard standard extends to accessory structures, which must have their lowest floor at or above the regional flood elevation under § 275-16C(2), and to manufactured home parks, where new, replacement and substantially improved units must have their lowest floor elevated to the flood protection elevation and be anchored against flotation or lateral movement under § 275-16C(11)(b). Public utilities and mechanical equipment placed in a flood-prone area must likewise be elevated to or above the flood protection elevation under § 275-14D(3)(a).