Impervious Surface means an area that releases as runoff all or a majority of the precipitation that falls on it. “Impervious surface” excludes frozen soil but includes rooftops, sidewalks, driveways, parking lots, streets, etc.
WHAT IS AN IMPERVIOUS SURFACE CALCULATION?
Percentage of impervious surface (IS) shall be calculated by dividing the surface area of the existing and proposed impervious surfaces on the portion of a lot or parcel that is within 300 feet of the ordinary high-water mark by the total surface area of that lot or parcel, and multiplied by 100.
(Existing and Proposed IS/Total Surface Area) x 100 = Percent IS
Impervious surfaces described in 11.5 shall be excluded from the calculation of impervious surface on the lot or parcel. If an outlot lies between the ordinary high water mark and the developable lot or parcel and both are in common ownership, the lot or parcel and the outlot shall be considered one lot or parcel for the purposes of calculating the percentage of impervious surface.
HOW MUCH IMPERVIOUS SURFACE CAN I HAVE?
Impervious Surface Standards Summary
Location
Allowed Impervious Surface Area
Permitted Impervious Surface area with Mitigation
General
15%
30%
Highly Developed Shorelands - Residential
30%
40%
Highly Developed Shorelands - Commercial/Business
40%
60%
Table illustrates a summary of section 11.3 and 11.4 in the Shawano County Shoreland Zoning Ordinance.
