Waukesha County, WI Environmental Rules: Flood Elevation Requirements (2026)
Key Facts
- Freeboard
- 2 feet above regional flood elevation
- Fill extent
- At least 15 feet beyond structure
- Fill height
- 1 foot above regional flood elevation
- Accessory structures
- Lowest floor 1 foot above flood elevation
- Permit required
- Floodplain Development Permit, Sec. 7.1
Summary
In unincorporated Waukesha County's floodfringe areas, new and substantially improved residential structures must have the lowest floor built two feet above the regional flood elevation on fill, not just at flood level. That two-foot cushion is the county's freeboard requirement, defined in the Floodplain Zoning Ordinance.
All new construction, including placement of manufactured homes, and substantial improvement of residential structures, shall have the lowest floor elevated to or above the flood protection elevation on fill. The fill around the structure shall be one foot or more above the regional flood elevation extending at least 15 feet beyond the limits of the structure.
Full Breakdown
3(1)(a) makes that the build-to line for the floodfringe. Any new construction, including placement of manufactured homes, and any substantial improvement of a residential structure in the floodfringe must have its 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 running at least 15 feet beyond the structure's limits. A narrow exception exists for a basement or crawlspace five feet or less in height that is not usable as living area: it may sit at the regional flood elevation itself if it is designed watertight, with walls substantially impermeable to water and structural components able to resist hydrostatic and hydrodynamic loads, but no floor of any kind may go below the regional flood elevation.
3(2) requires their lowest floor on fill at least one foot above the regional flood elevation rather than the full two-foot freeboard. 5. 3(7) and (8), consistent with Wis. Admin. Code SPS 383 and NR 811/812. 1 before any of this construction, filling, or grading begins.
Violations & Fines
Building below the required flood protection elevation without a floodplain development permit is a zoning violation enforced by the county zoning administrator, who can require elevation certificates from a registered professional engineer, architect, or land surveyor documenting the lowest floor and fill elevations actually achieved. Noncompliant structures also risk losing eligibility for National Flood Insurance Program coverage, since FEMA maps and flood insurance rates are tied to compliance with the adopted freeboard standard.
Frequently Asked Questions
How high above flood level must I build in the floodfringe?
Can I put a basement below the flood protection elevation?
Do accessory buildings need the full 2-foot freeboard?
Sources & Official References
Other rules in Waukesha County
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