CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A hip roof has a flat plan (footprint) area of 2,400 square feet and a slope of 8:12. Using a standard roof area factor table, the area factor for an 8:12 hip roof is 1.20. What is the actual roof surface area, expressed in roofing squares?
- A26.4 squares
- B28.8 squares
- C24 squares
- D31.2 squares
Show answer & explanationAnswer & explanation
Correct answer: B. 28.8 squares
Multiply the flat plan area by the area factor: 2,400 × 1.20 = 2,880 square feet. Convert to squares: 2,880 ÷ 100 = 28.8 squares.
Why the other options are wrong
- A. Uses an incorrect factor below 1.20.
- C. This is the flat plan area converted directly to squares without the slope factor.
- D. Uses a factor higher than the correct 1.20 value.
Hip Roof Area Factor
A multiplier from a standard roof area factor table converts a flat plan (footprint) area into actual sloped roof surface area for a given slope and roof type.
- Multiply footprint area by the slope's area factor.
- Factors are typically found in rafter/area tables by slope ratio.
- Convert final square footage to roofing squares by dividing by 100.
Memory trick: Flat footprint times the factor equals true roof area.