What is the most important factor when deciding the depth of a footing?

The most important factor when deciding the depth of a footing is the depth of the frost line. This refers to the maximum depth at which soil is expected to freeze during winter months. Ensuring that footings are placed below this frost line is vital for maintaining stability and preventing potential shifting or damage caused by soil expansion and contraction that can occur with freeze-thaw cycles. If footings are set shallower than the frost line, there is a greater risk that they will be subjected to freezing temperatures, which can lead to structural issues as the ground moves.

While factors like soil type, building height, and local building codes also play important roles in the design and safety of a foundation, the depth of the frost line is often the determining factor in preventing frost heave, making it crucial for ensuring the long-term integrity of the structure. Soil type influences how load is distributed, building height requires appropriate load considerations, and local codes provide regulations, but without proper frost depth, footings are at significant risk.