Grant County, WI Building Setbacks & Zoning: Lot Coverage Limits (2026)

Article IX of the Shoreland Protection Ordinance sets impervious surface standards. Section 316-35 says they apply to the construction, reconstruction, expansion, replacement or relocation of any impervious surface on a riparian lot or parcel and on any nonriparian lot or parcel located entirely within 300 feet of the ordinary high-water mark of any navigable waterway. Section 316-36 prints the formula: the surface area of existing and proposed impervious surfaces on the portion of the lot within 300 feet of the ordinary high-water mark, divided by the total surface area of that lot or parcel, multiplied by 100.

An outlot between the water and the developable lot counts with that lot when both are in common ownership. Section 316-37 is the general standard of up to 15%. Section 316-38A allows more than 15% but not more than 30%, and § 316-38B allows a permit with a mitigation plan meeting Article XIV for properties that exceed the standard but not the maximum in § 316-39A. Treated surfaces drop out of the calculation under § 316-39: surfaces treated by stormwater ponds, constructed wetlands, infiltration basins, rain gardens, bioswales or other engineered systems, or whose runoff discharges to an internally drained pervious area.

The application needs runoff calculations, documentation of the treatment, and an implementation schedule and enforceable obligation recorded with the Register of Deeds before the permit is issued. Lawful existing surfaces over the limit can be maintained and repaired, replaced with similar surfaces within the existing building envelope, or relocated or modified without increasing the percentage that existed on the effective date of the County shoreland ordinance (§ 316-40). Mitigation under § 316-50C requires at least five points, and reducing impervious surface to less than 15% on the lot earns 5.0 points.