What is a frost line depth chart?

A frost line depth chart is a map or graphical representation that indicates the depth at which water in the ground freezes, or the depth to which ice or frost penetrates the soil in a location. Governments and engineers use these charts in the construction of buildings, bridges and roads.

Factors that determine the frost line for an area include the area’s climate and average temperatures, the amount of moisture in the ground and the length of time the air temperature stays below freezing. This information is important because water expands when it freezes and can cause pipes to burst or structures to collapse unless they are set below the frost line.