How many rolls of R-19 insulation are required to insulate the roof of the garage shown in Figures 15.16 and 15.17? The insulation comes in rolls 23 inches wide by 56 feet long. The insulation is installed between the rafters, which are spaced 24 inches on center. From Figure 14.48 in Estimating in Building Construction, the slope length factor is 1.055.

What will be an ideal response?


Run = 24? / 2 = 12?

Length of rafter = 12? × 1.055 = 12.66?

Area of roof = 2 sides × 12.66? × 30? = 760 sf

Effective coverage per roll = 24? × 56? / 12 in per ft = 112 sf

Rolls of insulation = 760 sf of roof / 112 sf of coverage per roll = 6.78 rolls – Use 7 rolls

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