Wisconsin Footing Depth: 48 Inches or the Frost Line

Wisconsin does not adopt the International Residential Code for one- and two-family dwellings. It writes its own Uniform Dwelling Code, and that code states the footing rule directly: footings and foundations, including those for landings and stoops, shall be placed below the frost penetration level or at least 48 inches below adjacent grade, whichever is deeper. The phrase whichever is deeper is the part that matters. Forty-eight inches is a minimum that applies everywhere in the state, but where actual frost penetration goes deeper than that, the deeper figure governs. The rule explicitly reaches landings and stoops, which are the elements most often built shallow because they read as incidental rather than structural. A companion provision bars placing footings on frozen material at all, which in practice constrains winter construction independently of how deep the excavation goes.

Footing depth and the condition of the bearing surface are both checked at inspection before concrete is placed. A footing at 48 inches in an area where frost penetrates deeper does not comply, because the code takes the greater of the two. Placing a footing on frozen material is a separate violation regardless of depth. Limited exceptions exist under sub. (2) of the same section.