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Here we have again a wall made up of three different layers.
The first layer is wood siding,
which is outside, obviously.
And its R-value is given as 0.81, whatever the thickness
might be of that wood siding.
And we have a second later of fiberglass.
And this fiberglass thickness is given as 5 inches, and its
R-value is given as 3.7 per inch.
So we are using 5 inches.
5 times 3.7 would be 18.50.
And we have a third layer of drywall, and this drywall has
an R-value of 0.45 half-inch drywall.
When you add all these three layers up, you get a total
R-value of 19.76.
So the answer is 19.76 degrees Fahrenheit foot
square hour over BTU.
This is the composite R-value.