CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A roofing contractor is estimating materials for a low-slope commercial roof measuring 6,500 square feet. The plan calls for a modified bitumen roof system with a granular cap sheet that comes in rolls covering 100 square feet each, and a 4-inch side lap and 6-inch end lap for each roll. Assuming a 10% waste factor, how many rolls of cap sheet should be ordered?
- A65 rolls
- B78 rolls
- C72 rolls
- D85 rolls
Show answer & explanationAnswer & explanation
Correct answer: C. 72 rolls
First, calculate the base number of rolls needed without waste: 6,500 sq ft / 100 sq ft/roll = 65 rolls. Next, apply the 10% waste factor: 65 rolls * 1.10 = 71.5 rolls. Since you cannot order half a roll, round up to 72 rolls. The laps are accounted for in the 'covering 100 square feet each' which is net coverage.
Why the other options are wrong
- A. This is the number of rolls without applying any waste factor.
- B. This would result from a higher waste factor or an error in calculation.
- D. This is an overestimation, possibly from an incorrect waste factor or calculation error.
Cap Sheet Roll Takeoff
Calculating the total number of cap sheet rolls required for a low-slope roof by dividing the roof area by the net coverage per roll and then applying a waste factor.
- Net coverage per roll accounts for manufacturer-specified laps.
- Waste factors are crucial for accurate ordering.
- Always round up to the nearest whole roll.
Memory trick: Area to coverage, then add waste, like baking a pie with extra crust.