The frost line depth for most of Michigan is 42 inches. This is the depth at which groundwater present in the soil freezes. Though this is the standard depth, other factors play a part in determining the frost depth for a particular area.
Areas with nearby heat sources or asphalt generally remain warmer and do not freeze as deeply. Frost depth is taken into account when building, as footings and foundations are often required by law to be buried at a minimum depth to prevent damage. Pipes and water lines should also be buried below this line to prevent freezing.