How well insulation works is expressed by its R-value, which measures resistance to the flow of heat. The higher the R-value, the better it insulates per inch of thickness.
How Much Is Enough?
The amount of insulation recommended for your home is dependent on where you live, but here are some general guidelines:
- Attic Insulation: Houses in a cold climate should have a minimum of R-49 in the attic, which is equivalent to approximately 16″ of fiberglass insulation. Warmer climates only require an R-38 or higher, or about 12″ or more.
- Wall Insulation: While wall insulation is limited by the width of the studs, different materials provide higher or lower R-values. Fiberglass batts for standard 2×4 walls are now available in low, medium, and high density products that range from R-11 to R-15. Sprayed foam insulation in the same wall cavity can range from an R-14 to an R-28 depending on the product that is used.
- Floor Insulation: While there are additional considerations—such as venting and moisture problems—to take into account when you insulate under floors, the United States Department of Energy recommends an R-25 rating in cold climates and an R-11 in warmer parts of the country.
Comparative Insulation R-Values
The R-value per inch for different types of insulation varies depending on the brand and how it was installed, but here are some general comparisons from the Department of Energy:
|Insulation Type:||R-Value per Inch:|
|Fiberglass (loose)||2.2 – 2.9|
|Fiberglass (batts)||2.9 – 3.8|
|Cellulose (loose)||3.1 – 3.8|
|Stone Wool (loose)||2.2 – 3.3|
|Stone Wool (batts)||3.3 – 4.2|
|Cotton (batts)||3.0 – 3.7|
|Cementitious (foam)||2.0 – 3.9|
|Polyicynene (foam)||3.6 – 4.3|
|Phenolic (foam)||4.4 – 8.2|
|Polyisocyanurate (foam)||5.6 – 8.0|
|Polyurethane (foam)||5.6 – 8.0|