How to Measure the Heat Resistance in Thermal Insulation for the Attic

Determine the ideal R-value for your attic insulation. Thermal resistance of insulation is measured in R-values, and the US Department of Energy recommends insulating your attic to a value of R-38. But note that this recommendation depends somewhat on the unique climate in your area; exceptionally cold climates may require more insulation and very warm climates with mild winters may require slightly less.

Choose an insulation material that can deliver that R-value when installed. For most insulation materials, insulating to R-38 will require 10 to 14 inches of insulation, so if you cannot afford that much insulation, or if there is not enough room in your attic to install 10 to 14 inches worth, look for an insulation material with a higher R-value so that you can install less to the same degree of thermal resistance.

Determine where to install the insulation. R-values are mostly a function of the type of insulation and the amount and thickness of the insulation when installed; but R-values also depend somewhat on where the insulation is installed. For attics, there should be insulation along all the floor joists and sometimes right up to the eaves (though installation along the eaves requires installation of rafter vents as well). Install enough insulation so that you can see the insulation coming up above the floor joists but the joists are not completely covered with insulation. Adding insulation to the eaves along with the floor joists should deliver a R-value at or near the ideal degree of thermal resistance.