A gable roof covers a 60 ft by 40 ft rectangular plan. The slope factor for the 6:12 roof is 1.118. Before waste, how many roofing squares are needed?
Correct Answer
B) 26.8 squares
Plan area is 60 x 40 = 2,400 sf. Sloped roof area is 2,400 x 1.118 = 2,683 sf. Roofing squares are 2,683/100 = 26.8 squares. Other choices use plan area only, add waste not requested, or round to an unsupported value.
Why This Is the Correct Answer
Plan area is 60 x 40 = 2,400 sf. Sloped roof area is 2,400 x 1.118 = 2,683 sf. Roofing squares are 2,683/100 = 26.8 squares. Other choices use plan area only, add waste not requested, or round to an unsupported value.
Why the Other Options Are Wrong
Option A: 24.0 squares
sloped roof area, choice a: 24.0 squares backs into 0.89 when divided by 2683/100; the accepted setup gives 1 on that same base.
Option C: 29.5 squares
sloped roof area, choice c: 29.5 squares backs into 1.1 when divided by 2683/100; the accepted setup gives 1 on that same base.
Option D: 30.0 squares
sloped roof area, choice d: 60 x 6 / 12 gives 30.0 squares. That calculation follows multiplies two values and divides by the third.
Memory Technique
Keep a tag beside sloped roof area: if one number is skipped, the option drifts away from 26.8 squares.
Reference Hint
Open Roofing Construction and Estimating, Atcheson, 1995/2022 reprint; use the index entry or section for "Roof area and roofing square calculation" to confirm that Plan area is 60 x 40 = 2,400 sf.
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