For a roof slope of 8 in 12, the factor to convert plan area to actual area is

• A. 1.202
• B. 1.414
• C. 1.118
• D. 1.054

Answer: (A)

Converting plan area to the actual roof area uses the secant of the roof angle, since a sloped surface covers more area than its horizontal projection. The rise/run for an 8 in 12 roof is 8/12 = 2/3, so the factor is sqrt(1 + (2/3)^2) = sqrt(1 + 4/9) = sqrt(13/9) ≈ 1.202. Therefore, multiply the plan area by about 1.202 to get the actual roof area.