CSLB C-39 Roofing ContractorEstimating and PlanningEasy
A roof rises 6 inches over a horizontal run of 24 inches. Expressed as a standard roof pitch (rise per 12 inches of run), what is the slope?
- A4:12
- B2:12
- C6:12
- D3:12
Show answer & explanationAnswer & explanation
Correct answer: D. 3:12
Rise per 12 inches of run = (6 in ÷ 24 in) × 12 in = 3 in. Therefore the pitch is 3:12, a common low-slope roof pitch.
Why the other options are wrong
- A. This overstates the pitch beyond the calculated 3:12 ratio.
- B. This undervalues the rise-to-run ratio given.
- C. This would require a 12-inch rise over a 24-inch run, double the actual rise.
Converting Rise/Run to Standard Pitch
Any rise-over-run measurement can be converted to the standard 'X:12' pitch notation by scaling the run to 12 inches and adjusting the rise proportionally.
- Pitch is always expressed per 12 inches of horizontal run
- Formula: pitch = (rise ÷ run) × 12
- Used to select correct slope factor and material specs
Memory trick: Scale it to twelve to see what you've got.