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

The Shoreland Protection Ordinance's impervious surface standard, Section 3(t), applies to any riparian lot, or non-riparian lot entirely within 300 feet of the ordinary high water mark of a navigable waterway. Coverage is calculated by dividing total existing and proposed impervious area by lot area and multiplying by 100. Roadways and sidewalks as defined in Wis. Stat. 01, plus minor items like utility boxes, mailbox and birdhouse footings, fences, basketball hoop footings, and turf-stone surfaces that are mostly vegetated, are excluded from the math, as are "treated" surfaces under subsection 9 whose first half-inch of runoff is infiltrated or treated to a County or State stormwater standard, verified through a Stormwater Permit from the Land Resources Division.

The baseline cap is 15%. A property can reach 30% if it meets the Section 3(u) mitigation point system, which requires a native vegetative buffer, erosion control and an invasive-species management plan recorded through a deed restriction with the Register of Deeds. Lots designated "highly developed shoreline" under WDNR Chapter NR 115 criteria and mapped on the County GIS layer get higher baselines: 30% residential (40% with mitigation) and 40% commercial/industrial/business (60% with mitigation). Existing nonconforming impervious surface may be maintained, repaired, or replaced within the same footprint, but the percentage in place on October 1, 2016 may not increase. Every regulated surface needs a Zoning Permit from the Zoning Administrator before work begins.