Why Kansas Deck Footings Have to Go Below the Frost Line

Water in the soil around a footing expands when it freezes, and eastern Kansas sees that freeze-thaw cycle happen 80 to 110 times over an average winter, more than most homeowners assume. A footing poured above the frost line, roughly 30 to 36 inches deep in the Topeka area, gets pushed and shifted by that expansion year after year, which is why so many of the deck repairs we get called out for in Shawnee County trace back to a shallow footing rather than normal wear on the boards themselves. This is also why a deck built to spec in a warmer state isn't automatically safe to replicate here — frost depth is regional, and Kansas's is deeper than a lot of national deck-building guides assume.