Wisconsin Roof Snow Load: Set by Zone Map, Not Ground Load

This is a distinction that trips up anyone bringing habits from another state. Wisconsin's Uniform Dwelling Code requires that roofs be designed and constructed to support the minimum snow loads listed on the zone map, with the loads assumed to act vertically over the roof area projected upon a horizontal plane. The value being assigned is therefore a roof load, not a ground snow load. Most states publish a ground snow load and leave designers to derive the roof value from it using exposure, thermal and slope factors; Wisconsin publishes the roof figure directly from its zone map and states no ground snow load in this chapter at all. Sloped roofs are then adjusted from the mapped value by multiplying by the slope factor. If you need a ground snow load for Wisconsin, for a structural calculation that takes one as its input, the dwelling code will not give you one.

Enforced at plan review rather than as a citable offence. The failure mode specific to Wisconsin is substituting a ground snow load figure taken from a national source where the code calls for the mapped roof load, or vice versa. Because the two quantities differ, a design built on the wrong one is using a number the code never assigned to that site.