CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A rectangular building measures 24 feet by 36 feet. The roof has a 4:12 slope and 12-inch overhangs on all four sides. What is the approximate total roof surface area including overhangs, in squares (rounded to the nearest tenth)?
- A10.4 squares
- B8.6 squares
- C9.9 squares
- D11.2 squares
Show answer & explanationAnswer & explanation
Correct answer: A. 10.4 squares
Adding a 1-foot overhang on all sides increases the footprint to 26 ft × 38 ft = 988 sq ft. The 4:12 slope factor is 1.054, so total area = 988 × 1.054 = 1,041.4 sq ft ≈ 10.4 squares.
Why the other options are wrong
- B. This ignores the overhang addition entirely.
- C. This underestimates by using the raw footprint without the slope factor.
- D. This overstates the area by applying too high a slope factor.
Overhang-Adjusted Footprint Area
Roof area calculations must add eave and rake overhangs to the building footprint before applying the slope factor, since overhangs extend beyond the exterior walls.
- Add overhang distance to both length and width dimensions
- Overhangs typically extend 12-24 inches beyond walls
- Apply slope factor after adjusting footprint dimensions
Memory trick: The roof reaches farther than the walls below.