What is the R-Value of my Attic Insulation?
Attic Insulation is crucial for energy conservation. The higher the R-value of your attic insulation, the greater the insulating effectiveness. The R-value is a measure of insulation’s resistance to heat flow.
Determining your attic’s r-value is a matter of determining what type of insulation you have, how thick the insulation is, and how well it was installed. Also, the overall r-value of your attic may not be the same as the insulation in it, because heat flows around the insulation and through studs and joists. An infrared camera illustrates this very well.
Here are some common do-it-yourself materials used for attics and their R-values:
Insulation Type R-Value per inch
Blown Cellulose 3.7
Blown Fiberglass 2.8
Fiberglass batts 3.0*
*The quality of the installation is extremely important with insulation. Fiberglass batts have to be correctly installed for this R-value. If they are compressed, or if there are gaps the r-value drops substantially.
You can measure the depth of the insulation and multiply this by the r-value. The effective r-value takes into consideration how well it was installed. There are formulas to determine the degree to which these values drop, but the message is that installing batts is at least as important as the insulation itself.