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How Much Insulation You Will Need-Part 3

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On a new home, find out what the recommended R-value is for the type of heat you are planning to use for the location of your new home. Again, local electric and gas companies can provide this information to you or you can contact the Department of Energy.

On an existing home it is a little more complicated, but not hard. First, you need to identify what type of insulation is currently in your home. It may differ by the various locations in your home. In your attic for example, you may find batt or blanket fiber glass over the top of loose-fill cellulose. You may also find multiple layers of batt or blanket insulation. Next, you need to measure the thickness of each of these different types of insulation at the different locations. To help you with this process, take a regular sheet of notebook paper and make four columns. Label the first column ‘Location,’ the second column ‘Type Of Insulation,’ the third column ‘Inches Thick’ and the fourth column ‘R-value per Inch.’

The table below shows you the approximate R-value each inch of the various types of insulating materials provides. Use this chart to fill in the last column of your worksheet. One inch of fiber glass batts or blankets, for example, provides an approximate R-value of 3.2. To find the R-value of 4′ of fiberglass, multiply 4 x 3.2 to get an R-value of 12.8. Repeat this process of multiplying the number of inches thick and the R-value per inch of insulation for each area in your home. If you have two different types of insulation together, like our earlier example, find the R-value for each and then add them together.

 
R-VALUE
Insulation TypeR-Value per inch thickness
Fiberglass blanket or batt3.2
High-performance fiber glass blanket or batt 3.8
Loose-fill fiber glass 2.5
Loose-fill rock wool2.8
Loose-fill cellulose 3.5
Perlite or vermilculite 2.7
Expanded polystyrene board3.8
Extruded polystyrene board 4.8
Polyisocyanurate board, unfaced 5.8
Polyisocyanurate board, foil-faced 7.0
Spray polyurethane foam 5.9