Your Home Foundation: Frost Protection

Blankets Protecting Footer From Cold Temperatures

The recent photo above shows a newly excavated hole for a new home foundation being built in a cold weather climate. The vinyl materials on the ground are insulating blankets used for frost protection when building in freezing temperatures.  These blankets are placed in the spread footing locations immediately after digging the hole to help trap the heat in the ground.  Temperatures in the ground stay at a relatively constant temperature at a given depth below the frost line for a given geographic location. So, at the time you dig the hole for the home foundation, the soil may be a balmy 50 degrees Farenhiet in December. So as long as we get the frost protection in place right away, the ground will stay warm until we get the footings installed…even if the outside air temperatures are below freezing.

An alternative material for protecting a home foundation during construction in cold weather is straw.  Straw is a cheap material and is easy to install.  However, the straw will blow around in windy conditions and is more difficult to clean up.  Make sure the straw is removed from the perimeter of your home foundation before backfill as the material will break down causing settlement and odor issues (from decomposition).

If the ground is allowed to freeze prior to placing the footings for the home foundation, you run the risk of heaving/cracking.  Heaving occurs as the ground freezes and expands.  The expansion can be excessive where the soil is extremely wet. A footing that is allowed to heave should be removed prior to placing the foundation walls on top.  A heaved footing will have cracks weakening the material and has a higher potential for settlement in the future.  Settlement of a home foundation on a fully completed project can cost tens of thousands of dollars to repair.  You should never pour any type of concrete over frozen ground due to the potential for frost heave.

Footing with Insulating Blankets

In the photo above, the garage footings for a new home foundation have been poured and the blankets have been put back to keep the concrete and adjacent soil warm until the concrete sets up. The chemical process associated with the setting concrete is called hydration.  Placing the blankets on top of the curing concrete allows the heat from the hydration process to be maintained and allows the material to strengthen more quickly.  So, the blankets are placed after digging the hole to keep the heat in prior to footing placement, and then removed to form and pour the footings for the home foundation. Once the concrete sets up, the blankets are placed back over top to retain the heat from hydration of the concrete.

Owner-builders need to consider cold weather conditions when planning a new building project.  Be sure to get a price from your home foundation contractor to work in freezing temperatures (if you build in cold weather).  You will want to put language in your contracts that require your trades to protect their own work from cold temperatures and weather changes.  This would include admixtures for concrete as well as the installation and removal of insulation materials.  Make sure you include these extra costs in your budget as they can run as high as five percent of the total cost to build.  You don’t want to have cost over runs, and more importantly, you don’t want to build a home foundation that is anything but the highest of quality.

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