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

Jefferson County's floodplain zoning ordinance (Ch. 6, Art. III, Sec. 6-181, adopted by Ord. No. 2025-07 on July 14, 2025) defines "flood protection elevation" as the regional flood elevation plus two feet of freeboard, and defines "freeboard" as the safety margin that compensates for factors that push flood heights above a calculated level, including ice jams, debris accumulation, wave action, bridge and culvert obstruction, watershed urbanization, and loss of flood storage capacity. That two-foot freeboard standard drives the construction rules in every floodplain district. Under Sec.

6-247(1)a, new construction and substantial improvement of residential structures in the floodfringe district, including manufactured homes, must have the lowest floor elevated to or above the flood protection elevation on fill, with the fill extending at least one foot above the regional flood elevation for a minimum of 15 feet beyond the structure's limits. A basement or crawlspace floor may instead sit at the regional flood elevation only if it is engineered watertight to resist hydrostatic and hydrodynamic loads, but no floor of any kind may go below the regional flood elevation (Sec.

6-247(1)b). In the floodway district, structures permitted at all must have the lowest floor at or above the flood protection elevation or meet dry-floodproofing standards to that same elevation, and mechanical and utility equipment must likewise sit at or above the flood protection elevation (Sec. 6-217(b)). Manufacturing and industrial structures in the floodfringe carry the identical flood protection elevation floor unless floodproofed under Sec. 6-308 (Sec. 6-247(4)). Compliance is confirmed at occupancy: Sec. 6-304(c) requires a registered engineer, architect, or land surveyor to certify the as-built fill and lowest floor elevations before the zoning administrator issues a certificate of compliance.