Fond du Lac County, WI Environmental Rules: Flood Elevation Requirements (2026)

Fond du Lac County Code § 28-58(1)(a) sets the elevation standard for residential development in the floodfringe district: new construction, placement of manufactured homes and substantial improvement of residential structures 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 and at least 15 feet beyond the limits of the structure. The code's Article X definitions section pins down what "flood protection elevation" means: an elevation of two feet of freeboard above the regional flood elevation, so a structure's lowest floor sits two feet higher than the base flood mark the county's flood insurance rate maps show for that reach.

A basement or crawlspace floor may instead be set at the regional flood elevation only if it is designed watertight to the flood protection elevation, per § 28-58(1)(b). Accessory structures must also be built on fill with the lowest floor at or above the regional flood elevation under § 28-58(2). Nonresidential and manufacturing structures may floodproof to the same elevation instead of filling, under the certified floodproofing standards in § 28-105. Development in the floodway itself faces a stricter bar under § 28-43: an encroachment is prohibited unless an analysis by a Wisconsin-registered engineer shows no increase in flood elevation.

All of this applies only within the floodway, floodfringe and general floodplain districts mapped on the county's FEMA flood insurance rate maps for unincorporated Fond du Lac County; a land use permit from the zoning administrator (§ 28-101) is required before any fill, construction or substantial improvement, and a certificate of compliance, backed by a registered engineer's or architect's elevation certification, is required before occupancy.