Plan the scope
Adding a roof changes the structure; an existing deck should not be assumed capable of carrying it. Snow drift and sliding snow can create concentrated loads. The Wisconsin deck appendix says its standard design is not approved for concentrated loads exceeding 40 psf and requires engineering analysis for those loads. Roof design must be checked separately for the specific site.
- Open pergola or weather-shedding roof
- New post and footing loads
- Snow shedding from the house roof
Sources: Wisconsin Uniform Dwelling Code — SPS 325 Appendix B. Checked November 8, 2026. Confirm current requirements with your building inspector.
Built around Wisconsin conditions
Under Wisconsin’s prescriptive deck appendix, footings must bear on solid ground below frost penetration or at least 48 inches below finished grade, whichever is deeper. This is not a claim that every site has exactly 48 inches of frost. Soil, the house foundation and the proposed loads can require additional design.
Snow drift and sliding snow are explicitly identified as potential concentrated loads. Ask your contractor or designer to check the actual layout rather than treating a basic deck table as approval for a roof, hot tub or heavy planter.
Sources: Wisconsin Uniform Dwelling Code — SPS 325 Appendix B. Checked November 8, 2026. Confirm current requirements with your building inspector.