Insulating Exterior Concrete Slabs in Cold Climates

Exterior Concrete Slab Insulation Options

It is good practice to insulate concrete slabs in cold climates to protect the slab from frost penetration.  There are a number of different factors at play but the one thing that we always need to keep in mind is heat flow. Heat flows from hot to cold, and in the wintertime the ground temperature is warmer than the outside temperature the majority of the time. Keeping the heat flow principle in mind is the key to choosing the right approach to insulating the exterior concrete slab. If we know where the heat is, we can harness it and have a better chance of holding back the frost. The concrete slab insulation protects against the frost, but it’s because the rigid insulation is containing the heat the frost doesn’t penetrate.

What about just using concrete slab edge insulation?

This is an option many contractors and professionals have used in buildings for many years with success. It still can be part of an overall exterior slab insulation plan but depending on soil conditions and how cold it gets the slab should be looked at as a whole. The basis of slab edge insulation is to contain the heat at the outside perimeter of the heated or unheated building; this includes outside and inside. Rigid insulation is typically the preferred choice of insulation contractors and building envelope professionals. Rigid insulation is installed on the interior of the vertical foundation wall; this same type of insulation can be positioned vertically around the perimeter wall as well as horizontally, usually 4-10 ft into the building. Best practice is to install a semi-horizontal piece of rigid insulation on an angle around the perimeter of the building below the topsoil. This “wing” helps maintain the heat buildup under the insulation and essentially makes the frost go around the wing, and the foundation wall is that much more protected. This does two things. First, it helps increase the ground temperature, so heat loss is not as great. Second, it raises the ground temperature, decreasing the chance of frost moving in. The perimeter insulation and wing method, although effective on the edge, does not supplement a good overall frost reduction strategy in an outside concrete pad.

Why insulate an outside concrete pad?

  • Reduces or eliminates concrete heaving;
  • Aids in the curing of the concrete as moisture is pulled upwards;
  • Reduces maintenance cost of concrete slab;
  • Reduces concrete cracking;
  • Snow removal equipment does not catch concrete edges;
  • Future considerations: Putting a structure on the concrete pad;
  • Increases usable life span of the concrete slab.

Does rigid insulation contribute to concrete cracking?

No, placing the proper density of rigid insulation under the concrete slab does not contribute to concrete cracking. To ensure you minimize cracking in concrete slabs, do the following:

  • Properly mix the concrete;
  • Don’t add extra water;
  • Include expansion joints;
  • Cut control joints;
  • Use a water-to-cement ratio of less than 0.5;
  • Use fiber and wire mesh;
  • Rebar where required.

Installing a product like INSTA-PANELS® can increase the life expectancy of your concrete pad.  Call or e-mail an Insta representative to learn more about our insulation panel products.