CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A roof deck requires new plywood sheathing over 3,200 square feet. Standard sheets measure 4 feet by 8 feet (32 square feet each), and the contractor adds a 10% waste factor for cutting and irregular deck shapes. How many sheets of plywood should be ordered?
- A105 sheets
- B110 sheets
- C115 sheets
- D100 sheets
Show answer & explanationAnswer & explanation
Correct answer: B. 110 sheets
Apply the waste factor first: 3,200 × 1.10 = 3,520 square feet. Divide by the coverage per sheet: 3,520 ÷ 32 = 110 sheets.
Why the other options are wrong
- A. Reflects roughly a 5% waste allowance, too low.
- C. Overestimates by applying more than a 10% waste factor.
- D. This is the sheet count with no waste factor applied.
Sheathing Waste Factor
A percentage added to the base deck area to account for cut-offs and irregular framing when ordering plywood sheathing.
- Apply waste percentage before dividing by sheet coverage.
- Standard sheet is 4x8 ft = 32 sq ft.
- Round final sheet count up to a whole number.
Memory trick: Pad the area first, then divide by sheet size.