Do Deck Supports Shift with Ground Frost

Do Deck Supports Shift with Ground Frost

You are getting ready to build your new deck, regardless if it’s wood, composite or a stone deck, creating a solid base is key! For those of us who live in Canada, winter and ground frost is a real concern. So, do deck supports shift with ground frost? The bottom line is if you choose the appropriate deck support for your job and you install them correctly, you will not have any issues.

Let’s quickly look at what ground frost is and do deck supports shift with ground frost. Without getting too much into the science behind ground frost, moisture is absorbed and held within the ground materials and as this moisture freezes it expands. When this material expands, it is displaced and can displace objects within, around or on its surface.

To determine what deck supports are right for your job, here are some main points to consider; what do local building codes require, if anything? What is the size and weight of your deck, as well as the elevation of it? What are the soil conditions that the deck is being built on? Besides the building code aspects, all these other factors mentioned will determine whether your deck supports shift with ground frost.

Please keep in mind these points are for purposes of discussion and any actual building plans should be validated by a qualified source.

When it comes to soil conditions, if you are dealing with a sandy soil you will already have an advantage. Sandy soil will hold less moisture and will be less affected by any freeze-thaw cycles. Sand compacts well, with little to no settling over time, if compacted properly. With this situation, it is possible to create floating deck footings. These are appropriately sized concrete blocks or pads, placed as frequently and where they are required, as per the design of the deck.

On the other end of the soil spectrum is clay soil. This is the most problematic soil and will cause deck supports to shift with ground frost when using floating footings. Clay will hold a lot of moisture and as a result of freeze-thaw cycles, will cause it to move and shift.

In-ground footings are by far the best and most reliable way to prevent your deck supports shifting with ground frost. These are either concrete footings or mechanical screw piles, both of which are installed below the frost line. The depth of the frost line will be determined by the area of your location, the average cold temperatures and how long they last.

When installing concrete footings, you need to determine the diameter of the footing required, and it is important to bell the bottom. The idea of this is to create a base that will act as an attached base pad, that is wider than the footing itself. This accomplishes two things: provides more support to the bottom of the concrete footing and, more importantly, prevents the deck supports from shifting with ground frost. Have you ever seen a fence installed and after one winter all the posts are pushed up and sideways? This is caused by the installer digging holes straight down and pouring cylindrical footings that are easily pushed up by ground frost. In some regions of Canada, you will find ground frost over 36” deep. When designing your concrete footings, it is important to determine the load requirements for each to ensure they are constructed appropriately.

This is why mechanical screw piles are the best choice to prevent deck supports shifting with ground frost. With mechanical screw piles, there is no guess work in ensuring you have the correct footings for your deck. Most reputable screw pile companies are able to recommend the appropriate size of pile, depth and torque it should be driven to, based on the size and weight of the deck and snow loads where it is being installed. Plus, the design and nature of a screw pile prevents it from being pushed up.

As you can see there are several choices when it comes to choosing the supports for you deck. If you select the appropriate one for your job, you will have no issues with your deck supports shifting due to ground frost.