Our decks go through a lot over the winter months, and one of the most destructive forces is frost. Although most of us think of it as being icy lacework on windows or white frost on autumn leaves, it goes deeply beneath the surface to cause devastating damage to your deck.
How it Works
This destructive element is called frost heave, and happens when sandy soils freeze. When they freeze, they expand and lift anything on the surface. The Wikipedia image to the right demonstrates this principle beautifully. The lift can get to at least 4”, which is enough to cause serious structural problems.
Preventing Frost Heave
The structural imbalance caused by the lifting ground causes instability in your deck’s supports and floor. When this happens, it must be torn down and replaced. The only way to prevent frost heave is to make sure the concrete footings are anchored in soil that won’t freeze from year to year. According to the Minnesota State Building Code, that means that footings must extend at least 42” down in Southern Minnesota, and at least 60” in the north.
However, even when you plant the footings deep enough, it’s possible that the freezing soil can still lift the footings by gripping the cement. One way of doing this is to either install waxed cardboard tubes, or sonotubes, around the footings before you put them in. This prevents the surrounding soil from grabbing the underground cement. Another way to prevent heaving is to pour the cement into a bell shape at the bottom to hold the structure in place over the winter. Add iron rebar to give the footings enough strength the resist cracking from the force of frost forming around it.
Since Iron River Construction designs and installs decks, we’d be happy to help you if you had frost heave this year, and prevent it from happening in the future. Now is a great time to evaluate what happened last winter, and then take corrective action so it won’t occur again.