Core TradesQuestion 160 of 700
A wall uses R-15 cavity batt insulation plus R-6 continuous exterior rigid insulation. Ignoring framing and air films, what is the combined nominal thermal resistance of these two insulation layers?
a.R-21
b.R-9
c.R-15
d.R-90
Explanation
Thermal resistances of layers in series add together, so R-15 + R-6 = R-21. R-9 subtracts the values, R-15 ignores the continuous insulation, and R-90 incorrectly multiplies them. Series R-values are always summed.
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