Evaluating the R-value of Insulation Previously Installed in Existing Homes
Calculator for determining the R-value of your existing insulation:
Calculator for determining how much insulation you need to add:
Calculator for determining the approximate thickness you need to add:
Insulation type R-value per inch of thickness are listed below:
Fiberglass batt or blanket (3.2 inches)
High performance fiberglass batt or blanket (3.8 inches)
Loose-fill fiberglass (2.5 inches)
Loose-fill rock wool (2.8 inches)
Loose-fill cellulose (3.5 inches)
Perlite or vermiculite (2.7 inches)
Expanded polystyrene board (3.8 inches)
Extruded polystyrene board (4.8 inches)
Polyisocyanurate board, unfaced (5.8 inches)
Polyisocyanurate board, foil-faced (7 inches)
Spray polyurethane foam (5.9 inches)
Check out the information on the product insulation packaging to find out the actual thickness for any insulation for new buildings.
For new homes check out this calculator:
Insulation calculator for existing houses 
