The diagram below shows the dividing line. The Minnesota State Building Code requires footings to be a minimum of 42” deep in the southern part of the state, and a minimum of 60” deep in the northern part of the state. Decks constructed near wetlands will have an increased potential for frost heave. Outdoor temperatures obviously make a difference, and so does proximity to water. When it’s a winter with very little snow, like the type Minnesota experienced in 2011-2012, the frost depth will be much deeper than usual. When there is a lot of snow on the ground, the snow acts like a layer of insulation and reduces the frost depth. How deep do footings need to be to prevent frost heave? There’s no magic number. This is why it’s so important for deck footings to extend down below the frost line. Sandy, well drained soils aren’t particular susceptible to frost heave, while soils with higher clay content are prone to frost heave. When deck footings aren’t poured deep enough, decks can heave. The goal is to have this chunk of concrete go deep enough in to the ground so that the bottom rests on soils that never freeze, which should prevent the soils from pushing the footing up. The most common deck footing is basically a big chunk of concrete poured in to a hole in the earth. When a deck is attached to a building, the part of the deck that gets supported by the earth needs to have proper frost footings. Here’s one more photo showing major frost heave at a deck. The deck shown below had severe frost heave in the middle and against the house, and had to be completely torn down and rebuilt because the deck was so severely heaved in the middle. The right side had obviously heaved several inches. The photo below shows a Maple Grove deck that we recently inspected in the middle of an April snow storm. Without a doubt, some of the worst frost heave I’ve come across has been here in Maple Grove. I once lived in a townhouse in Saint Louis Park with a patio that would heave about 4” during the winter it got so bad that I could barely open my storm door during the winter. Wikipedia has a nice illustration of how this works, shown below. When expansive soils freeze and expand, the earth rises. Today I’ll explain how this works, why it matters, and what steps can be taken to help prevent damage from frost heave when building a deck. As the popularity of these increase they are likely to be more common place.One of the most common problems with decks in Minnesota is frost heave. Some of the local building supply companies are also starting to carry them. We purchase them from a local precast concrete supplier that makes septic tanks, manhole structures and misc concrete products. Since writing this article quite a few people have inquired about where to buy precast concrete piers. Be sure to come back and continue to follow this series as we build this new home. The piers are 54″ tall so you can have the base at 48″ (depth of frost protection here in NH) and still have 6″ above finished grade. Now the flip side of this is these are really only good when you have an excavator to dig a large hole and something to pick them up with. And the best part is you don’t have to worry about the weather. ![]() The piers have a threaded insert cast into the top so you can connect your porch or deck posts to them. They have a very large base for increased bearing capacity. Precast concrete piers offer several benefits compared to sonotubes. Then you also face the issue of whether or not you have sufficient bearing capacity. If the weather goes bad, which it does around here all the time, then the sonotubes can get wet and collapse before you get the concrete in them. In theory that works pretty well but my experience over the years has been nothing short of frustrating when it comes to building piers with sonotubes. Traditionally you would dig a hole in the ground, install a sonotube and then pour concrete into the hole. The new house has a front porch and rear deck for a hot tub so we installed the precast concrete piers to support the structural framing. On a recent project, Total House Construction Series – Foundation to Finish, I wanted to point out how we used precast concrete piers. Precast concrete piers are really great and we use them exclusively for porches and decks when we build new homes. ![]() In a previous posts I wrote about Porch and Deck Pier Footings and I highlighted a really great construction product, the precast concrete pier.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |