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Foundation

Basements and crawlspaces
Insulating your basement up to R-10 can help reduce energy costs by up to 12 percent.
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Many Midwestern homes are built with a bare concrete foundation - with an R-value of one, concrete walls provide almost no resistance to the cold.

To achieve the recommended R-10 value, your builder can attach rigid foam board insulation to the basement walls, then cover it with gypsum drywall boards for fire protection. If the basement will be finished, your contractor might construct 2x4 stud walls and install batt or blanket insulation.

FoundationInsulated concrete forms

It may sound a little strange, but Styrofoam blocks can be a great way to increase energy efficiency. The hollow foam blocks, called insulated concrete forms , fit together like Legos and are reinforced with steel rebar.

After concrete is poured into the hollow channels, the blocks become a well-insulated, strong, water- and insect-resistant foundation.

Insulating the foundation exterior

Builders in some areas of the country insulate the exterior of the foundation with rigid foam boards between the concrete block and the siding.

One disadvantage of this method is that moisture, insects or ground movement can damage some exterior insulation. If your builder recommends this method, be sure to verify that the insulation to be used is guaranteed for exterior use.

Don't forget the crawlspace and sill box

Whether you choose to insulate the interior or exterior of your basement - or both - it's important to remember the crawlspace and sill box areas.

A crawlspace should be insulated to keep heat from escaping. If the area is unheated, it should also be ventilated to prevent condensation and moisture damage.

There are two methods for insulating crawlspaces:

  • Drape fiberglass batts along the wall - this is the preferred approach.
  • Install batt insulation on the ceiling of the crawlspace.

The sill box is the area between the foundation and the floor joists. This area should be insulated the same as the wall above.


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If you are vision-impaired or have some other disability under the Americans with Disabilities Act or a similar law, and you wish to discuss potential accommodations related to shopping or ordering on or using the benefits of our website, please contact Alliant Energy at 1-800-ALLIANT (800-255-4268).