Book 24, Question 9
What is the frost line, and why are pipes buried below it?
In cold places, the ground freezes from the top down in winter. The frost line is the deepest point where the ground freezes. In southern Ontario it is about 4 feet down, and in colder parts of Canada it can be much deeper. Water pipes and building foundations are placed below that line, so freezing and expanding ice does not crack them.
More fun facts
- In cold places, the ground can freeze from just a few centimeters deep in mild areas to 2 meters or more in colder regions.
- Air temperature is the biggest thing that decides how deep the ground freezes.
- Snow and fallen leaves act like blankets, so soil in the woods rarely freezes, even in very cold winters.
- When the ground freezes deeply, it can freeze water and sewer lines and even lift buildings.
- Local building rules help make sure water and sewer lines are buried below the depth of frost.
- Garden sprinkler lines sit close to the surface, so people drain them before the soil freezes.
Sources: U.S. Department of Agriculture
Questions kids ask
Does snow keep the ground from freezing?
Snow works like a blanket that holds in the ground's warmth, so soil under snow freezes less deeply.