Insulation is rated by its R-value, which measures its thermal resistance or how well it holds back heat. The higher the R-value, the better. Bare concrete walls are about R-1, while attic insulation in newly-built Midwestern homes usually measures about R-44.
R-value is proportional to the insulation's thickness, but it also depends on the type of material and its density. The more air pockets an insulating product has, the higher the R-value. For example, R-38 attic insulation may be 12 inches of fiberglass batts, 10 inches of rock wool loose-fill or seven inches of expanding foam.
Different areas of your home need different levels of insulation. The list and chart below show the recommended R-values and estimated insulation amounts for homes in the upper Midwest:
For recommended levels specific to your home and location, try the U.S. Department of Energy’s ZIP-Code Insulation Calculator.
The best place to start is the attic - you'll get the greatest impact by adding insulation here. If you upgrade your attic insulation from three inches to 12 inches, you could save up to 20 percent on your heating costs - and 10 percent on your air conditioning costs!
If you heat your home with electricity, proper insulation is even more crucial, because electric heat is costlier and less energy-efficient. The U.S. Department of Energy recommends R-49 attic insulation for homes with electric resistance (baseboard) heating.
Improving sidewall insulation in an existing home is more difficult, but it can help lower your energy costs by up to ten percent. For existing homes, loose-fill insulation can be blown into wall cavities through holes cut under exterior siding. Or if you're replacing your siding, your contractor can add sheets of rigid foam insulation on top of the sheathing.
Basement and foundation insulation can also lower heating bills by five to ten percent. If you have a crawlspace, insulating the walls in this area can help you save another five percent.