CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A roof has three valleys, each measuring 40 linear feet, for a total valley length of 120 linear feet. Valley flashing rolls provide 50 linear feet of net coverage after required overlap. How many rolls must the contractor purchase?
- A3 rolls
- B2.4 rolls
- C2 rolls
- D4 rolls
Show answer & explanationAnswer & explanation
Correct answer: A. 3 rolls
Total valley length is 3 × 40 = 120 linear feet. Dividing by the 50-linear-foot net coverage per roll gives 120 ÷ 50 = 2.4 rolls. Since partial rolls cannot be purchased, the contractor must round up to 3 full rolls.
Why the other options are wrong
- B. Incorrect: this is the raw mathematical result, but materials must be purchased in whole rolls.
- C. Incorrect: underestimates by not covering the full 120 feet.
- D. Incorrect: overestimates and would leave excess unused material beyond a reasonable margin.
Valley Flashing Takeoff
Valley flashing rolls are purchased based on total linear footage of all valleys divided by the roll's net coverage, always rounded up to a whole roll.
- Add all valley lengths together first
- Divide by net coverage per roll after overlap
- Always round up to the next whole roll for material orders
Memory trick: Valleys collect water and rolls, so round every fraction up.