Rising deck every year from frost

by Joe Roch
(Montreal)

I have a deck which was built about 20 years ago. The problem it is rising in the corner every year more and more.

At first I thought it was the cold but when the earth unfreezes the deck stays very high and never goes down. I do have a cedar tree next to the deck but I doubt that the roots are causing the rise.

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Jan 18, 2013
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Very Interesting
by: Editor - Rich Bergman

That is very interesting and may help out. The concept of insulating around a footing like your deck may alleviate the risk of heaving caused when ice grips the sides of the pier because it may not freeze there any more.

However, even if you insulate under the pier footing, the soil still may freeze if the foam is not below the freeze depth of the soil. And so the entire footing could theoretically still be lifted up.

I think the foam is a good idea though and there is a new product that is used for fence posts and the like and is a foam mix - two parts. And it replaces concrete.

Thanks for sharing your experience. This will help out other people on the site.

Jan 17, 2013
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Paralized Footings
by: Anonymous

I tiled under my deck to "de-water" the clay soil. I also buried styrene insulation sheets over the footings to minimize frost depth under footings. I also replaced wood posts with steel jack posts so I can adjust deck height if needed.

I also redid some footings by jack hammering them out and pouring footings with pier tubes and mushrooming the concrete at the bottom. Some one advised using styrofoam peanuts in the back fill to keep the frost from penetrating as deep.

Apr 22, 2012
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Frost Heaving concrete piers and possible solutions
by: Editor - Rich Bergman

What is happening here is typical frost heave and this occurs when the bottom of a post or particularly the underside of a footing is not set below the frost line.

Ice forms in soil that contains water and if the ice under the bottom of the post is significant enough it will expand - as water uniquely does when it freezes and this will push the post upward. If you have a bell shaped footing this tends to resist this upward force. But a footing should always have at least its underside below the frost line to not be at risk.

If you have footings that are cylindrical - say 10" or 12" without any bell shaped footing the ice can push the bottom of the concrete pier upwards, just like the bottom of a fence post because the surface area is actually quite significant.

In the spring when the ice melts the soil liquifies and dribbles and drains back down and fills the void created underneath the footing or post with a slurry of soil an muck. This then solidifies to its natural state when the excessive water dissipates and then prevents the post or footing from descending to its original position.

As this occurs annually in a one way direction, you only see the post or pier rising a bit each year.

So the only solution for you is to unfortunately temporarily support the deck and excacate each footing and dig it deeper and rebuild a new footing lower than the frost level.

If you use deck blocks and enough of them to ensure the weight of the deck does not cause them to sink into the soil that will now make it a floating deck and it will move annually up and down but not remain higher each year.

Also there are other floating deck footing systems that anchor into the soil and provide more ridigity then deck blocks and won't heave either because they do not have large flat surface areas at the bottom where this phenomenon can occur. They are pointed spikes or helical anchors and they won't move out of their relative position in the soil even if it freezes like a flat bottomed post of pier would.

So I hope these tips can help you out.

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