Preventing Deck and Patio Pilings from Frost Heaves

Introduction:

The novice DIY homeowner who plans on building a deck or patio in areas where there is deep freezing during the winter should be aware that these support posts will heave up out of the ground when the ground freezes. When the pilings heave it raises the whole structure and more often than not you wind up with an out of level and very twisted structure. This happens more often than you might think and the problem can easily be avoided.

You can avoid these frost heaves by taking a few precautions. First, the pilings must be deep enough in the ground so the frost does not affect them. Depending upon the serenity of the winter weather where you live depends how deep they should be in the ground. A good rule of thumb is that the bottom of the pilings should be at a minimum of 42 inches below the grade of the surface in areas where the frost deeply penetrates the ground. In addition, the bottom of the piling or support column should have approximately six inches of crushed stone for water drainage. This will allow any water to drain off and eliminate freezing. If water freezes at the bottom of the piling the piling will rise up as the frozen water expands.

A few years ago I helped a neighbor install an extensive second story deck that included a set of stairs. We had the pilling at least 42 inches in the ground but the earth has solid clay. Clay does not observe water. The water pooled at the bottom of the pilings and the whole deck rose approximately six inches. In the spring we supported the deck and dug out the pilings. After placing a generous amount of crushed stone at the base of the pilings we leveled the deck and stairs. After many severe winters the deck never heaved up again.

Preventing deck and patio pilings from frost heaves

·       Dig the hole at least 42 inches below the surface grade. If you live in an area where winters are less severe 24 to 36 inches may be adequate. A good quality posthole digger can do the job.

·       Dump in six inches of ¼ to ½ inch of stone for drainage.

·       Insert a six or eight inch sonotube and trim the top to the desired level. Use a level to ensure that it is standing straight in the hole.

·       Fill the sides of the hole with earth to support the sonotube.

·       Fill the sonotube with concrete all the way to the top.

·       Place a post support bracket in the wet concrete.

·       Let the concrete harden overnight.

In place of sonotube pilings you can use precast tapered columns. They do a great job but you will need heavy lifting equipment to handle them as they weigh several hundred pounds. 

That’s all there is to it.

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