Question

Suppose that the insulating properties of the 100 m2 roof of a house come mainly from an “R-40” layer of insulation. (R-40 means 40 foot2 ·hour· ◦F Btu , which in metric units is 7.0 m2 · ◦C W .) (a) If the inside-outside temperature difference is 25◦C, how much heat per unit time (in watts) is lost through the roof? (b) How thick a layer of fiberglass would achieve this R-value? (c) How thick would a single layer of glass have to be to achieve the same R-value? (d) How thick would a single layer of trapped air (for example, trapped between two thin layers of glass, so that convection is minimized) have to be to achieve the same R-value?

Answer 1