CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A roof has 2,400 square feet of deck area requiring new plywood sheathing. The contractor uses standard 4-foot by 8-foot sheets (32 square feet each) and applies a 10% waste factor for cuts and hips. How many sheets should be ordered?
- A83 sheets
- B88 sheets
- C80 sheets
- D75 sheets
Show answer & explanationAnswer & explanation
Correct answer: A. 83 sheets
Applying the 10% waste factor: 2,400 × 1.10 = 2,640 square feet needed. Dividing by 32 square feet per sheet gives 2,640 ÷ 32 = 82.5, which rounds up to 83 sheets since partial sheets cannot be purchased.
Why the other options are wrong
- B. Incorrect: overestimates beyond the properly calculated waste-adjusted total.
- C. Incorrect: does not correctly apply the 10% waste adjustment.
- D. Incorrect: this figure ignores the waste factor entirely (2,400 ÷ 32 = 75).
Sheathing Material Takeoff
Plywood or OSB sheathing quantities are found by applying a waste factor to the roof area and dividing by the sheet's coverage area.
- Standard sheet size is 4x8 feet = 32 square feet
- Waste factor accounts for cuts around hips, valleys, and edges
- Always round the final sheet count up to a whole sheet
Memory trick: Add the waste before you divide the space.