Spray & Attic Insulation
Forming a true thermal seal, spray foam insulation has the ability to reduce utility bills over standard construction techniques. That means your potential savings can be huge. Still, some people may be tempted to use a less expensive, but largely inferior, conventional insulation when building their home. This is a big mistake. Why? Because building with spray foam Insulation only affects your mortgage payments marginally, perhaps by a few dollars, but your monthly utility bill could drop by a hundred dollars or more. With spray foam Insulation you start saving right away, and continue to do so for the entire life of your home.
Installed insulation R-value: The installed insulation R-value depends somewhat on the system manufacturer but generally speaking, high density foam (2.0 pcf) ranges between R-5.5 and R-6.5 per inch for the aged R-value, and low density foam (0.5pcf) has an R-value of approximately R-3.6/inch. Since high density foam is generally installed short of the cavity to avoid trimming, the installed insulation R-value is approximately R-30 (using R-6/inch). Low density is generally installed deliberately overflowing the cavity and trimmed off resulting in an R-value of approximately R-21.
Whole-wall R-value: Using two dimensional heat flow analysis with thermal bridging effects and average framing factors, it is clear that the thermal bridging through the framing, bottom plate, and top plate reduces the effectiveness of the spray foam insulation. The R-value of the high density spray foam wall decreases from an installed R-value of R-30 to approximately R-20, a decrease of R-10 because of thermal bridging. The low density spray foam wall decreases from an installed insulation R-value of 21 to a whole wall R-value of approximately R-16.
Air Leakage Control: Both low density and high density foam form an air barrier decreasing thermal losses through air leakage. Air leakage is still common under the bottom plate and at the rim joist if these areas are not detailed correctly.1
Typical Insulation: Low density 0.5 pcf foam, or high density 2.0 pcf foam.