CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A residential roof has a total surface area of 2,800 square feet, and the specifications call for two layers of #30 felt underlayment. Each roll of #30 felt covers 200 square feet net. How many rolls of #30 felt should be ordered for this project, accounting for a 10% waste factor?
- A31 rolls
- B37 rolls
- C28 rolls
- D34 rolls
Show answer & explanationAnswer & explanation
Correct answer: A. 31 rolls
First, calculate the total square footage needed for two layers: 2,800 sq ft * 2 = 5,600 sq ft. Then, apply the waste factor: 5,600 sq ft * 1.10 = 6,160 sq ft. Finally, divide by the net coverage per roll: 6,160 sq ft / 200 sq ft/roll = 30.8 rolls. Round up to 31 rolls.
Why the other options are wrong
- B. This is an overestimation, possibly from an incorrect waste factor or calculation error.
- C. This only accounts for a single layer of felt and no waste factor.
- D. This would result from a higher waste factor or an incorrect calculation of layers.
Underlayment Roll Calculation with Waste
Determining the total number of underlayment rolls needed by considering the roof area, number of layers, net coverage per roll, and an added waste factor.
- Waste factors are essential for accurate material ordering.
- Always round up to the nearest whole roll.
- Net coverage per roll accounts for overlaps.
Memory trick: Layers + Waste = Rolls to order, like a recipe for a perfect cake.