CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A gable roof with two valleys has a total roof surface area of 2,600 square feet. To account for additional cutting and waste caused by the valleys, the estimator adds a 15% waste factor. How many roofing squares should be ordered, rounded up to the nearest whole square?
- A28 squares
- B29 squares
- C26 squares
- D30 squares
Show answer & explanationAnswer & explanation
Correct answer: D. 30 squares
Apply the 15% waste factor: 2,600 × 1.15 = 2,990 square feet. Convert to squares: 2,990 ÷ 100 = 29.9, which rounds up to 30 squares since partial squares cannot be ordered.
Why the other options are wrong
- A. Reflects only about a 7–8% waste allowance, too low.
- B. This is the unrounded 29.9 truncated instead of rounded up.
- C. This is the base area without any waste factor applied.
Valley Waste Factor
Valleys require extra shingle cutting, so estimators add a waste percentage (commonly 10-15%) to the base roof area.
- Multiply base area by (1 + waste %).
- Always round up partial squares.
- More valleys or complexity may increase the waste percentage.
Memory trick: Valleys cut into shingles, so pad the order upward.