Portage County, WI Environmental Rules: Stormwater Management (2026)

Sec. 7.1.2(1)(b)4.b of the Portage County Zoning ordinance requires that any single accessory building, or cumulative total of accessory buildings, exceeding 2,000 square feet come with a stormwater control plan submitted to the Planning and Zoning Department for review and approval before a Zoning Permit is issued. This threshold sits inside the county's broader accessory-building standard for the R2 Single Family Residence District, which caps total accessory square footage at 2,800 square feet on lots under two acres and 3,200 square feet on larger lots.

Beyond the 2,000-square-foot stormwater trigger, the Planning and Zoning Department may also require increased screening or larger setbacks for individual accessory buildings of that size. In Planned Development Districts, the county applies a more detailed construction-site erosion and stormwater standard: an approved stormwater control plan must be designed to control runoff from a 25-year storm event, capturing all runoff from impervious surfaces, using standards from the Wisconsin Construction Site Best Management Practices handbook and at least six inches of vegetated topsoil. A zoning permit will not issue for a covered project until the Planning and Zoning Department has reviewed and approved the required plan, giving the county a direct check on runoff before large accessory structures or planned developments are built.