An R-value indicates insulation’s resistance to heat flow. The R-value depends on the type of insulation and includes its material, thickness, and density. When calculating the R-value of a multilayered installation, add the R-values of the individual layers. Installing more insulation in your home increases the R-value and the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness.
The effectiveness of insulation’s resistance to heat flow also depends on how and where the insulation is installed. For example, insulation that is compressed will not provide its full rated R-value. The overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. Therefore, it’s important to properly install your insulation to achieve the maximum R-value.
The amount of insulation or R-value you’ll need depends on your climate, type of heating and cooling system, and the section of the house you plan to insulate.
Different insulation types, materials, and thicknesses have different R-Values. For instance, to get R-30 insulation, you need a layer of vermiculite more than a foot thick, while you need only a few inches of cellulose or foam.
This means that when you compare insulation, never compare thicknesses; only compare R-values!
TYPICAL R-VALUES FOR SOME COMMON INSULATION MATERIALS
TYPICAL R-VALUES PER INCH
2.13 - 2.4
Rock Wood, loose-fill
3.0 - 3.3
Rock Wool, batts
3 - 3.85
2.2 - 2.7
Fiberglass, rigid panel
2.8 - 3.8
High-density fiberglass, batts
3.7 - 4.3
3.2 - 3.8
3.2 - 3.8
Cotton, batts (Blue Jean Insulation)
Icynene, loose-fill (Pour Fill)
Molded Expanded Polystyrene (EPS)
3.8 - 4.4
Extruded Expanded Polystyrene (XPS)
3.8 - 4.4
Polyurethane Spray Foam, open-cell
3.6 - 3.7
Polyurethane Spray Foam, closed-cell
7.0 - 8.0
Polyurethane Foam, board
5.6 - 8.0
2008 U.S. Department of Energy (DOE) R-Value Recommendations for New and Existing Homes
The following 2008 Department of Energy zone recommendations are based on comparing estimated future energy savings to the current cost of installing insulation. The DOE gives a range for many locations for the following reasons:
Energy costs vary greatly over each zone
Installed insulation costs vary greatly over each zone
Heating and cooling equipment efficiency varies from house to house
Best estimate of future energy costs may not be exact.1