Based on the roof shown below, estimate the amount of 30-pound underlayment required. Assume single coverage, a crew-error waste of 4 percent, and a slope of 6 in 12.
Note: the factor comes from a table like the one shown below
Actual Roof Area = 2,250 sf x 1.118 = 2,515.50 sf = 25.16 Roofing Squares
Note: 1.50 is the update by which you multiply the run to get the actual area.
22.5’ x 8 (the number of hips and valleys) is 180’
Find a table which gives you the coverage for the different types of underlayment.
From the table, you can see that 1 roll of # 15 underlayment covers 4 squares, so
28.61 squares/2 squares per roll = 14.305 rolls is the answer.