Evaluating the R-value of Insulation in Existing Home

Table 2. Evaluating the R-value of Insulation Previously Installed in Existing Homes

 

(Includes Effects of Aging and Settling).

Insulation type	R-value per inch of thickness
Fiber glass blanket or batt	2.9 to 3.8 (use 3.2)
High performance fiber glass blanket or batt	3.7 to 4.3 (use 3.8)
Loose-fill fiber glass	2.3 to 2.7 (use 2.5)
Loose-fill rock wool	2.7 to 3.0 (use 2.8)
Loose-fill cellulose	3.4 to 3.7 (use 3.5)
Perlite or vermiculite	2.4 to 3.7 (use 2.7)
Expanded polystyrene board	3.6 to 4 (use 3.8)
Extruded polystyrene board	4.5 to 5 (use 4.8)
Polyisocyanurate board, unfaced	5.6 to 6.3 (use 5.8)
Polyisocyanurate board, foil-faced	7
Spray polyurethane foam	5.6 to 6.3 (use 5.9)

Use this formula to determine the R-value of your existing insulation:

	×		=
Thickness (inches)	×	R-value per inch	=	Total R-value

Use this formula to determine how much insulation you need to add :

	-		=
Recommended R-value	-	Existing insulation R-value	=	R-value needed

Do you want to know if you have the space available to add the insulation you need? Then use this formula to determine the approximate thickness you need to add:

	÷		=
R-value needed	÷	R-value per inch	=	Approximate thickness needed

However, remember to use the product information on the insulation packaging to determine the actual thickness for any new insulation.

Courtesy of the DOE