The frost depth depends on the climatic conditions of an area, the heat transfer properties of the soil and adjacent materials, and on nearby heat sources.
The maximum frost depth observed in the contiguous United States ranges from 0 to 8 feet (2.4 m).
For this reason, foundations are generally built below the frost depth.
Water and sewage pipes are typically buried below the frost line to prevent them from freezing.
Due to additional cost, this method is typically only used where deeper trenching is not an option due to utility conflicts, shallow bedrock, or other conditions that make deeper excavation infeasible.