CSLB C-39 Roofing ContractorEstimating and PlanningMedium
A synthetic underlayment roll covers 10 squares (1,000 sq ft) net after overlap. The total roof area is 32 squares. Applying the standard 10% waste factor for laps and cuts, how many rolls should be ordered?
- A6 rolls
- B4 rolls
- C3 rolls
- D5 rolls
Show answer & explanationAnswer & explanation
Correct answer: B. 4 rolls
32 squares × 1.10 waste factor = 35.2 squares needed. 35.2 ÷ 10 squares/roll = 3.52, which rounds up to 4 rolls.
Why the other options are wrong
- A. Significantly over-orders material.
- C. Ignores waste factor, leaving insufficient material.
- D. Overstates the requirement beyond calculated need.
Underlayment Roll Coverage
Underlayment rolls are rated for net coverage after overlap; waste factors must be added to account for laps, valleys, and cutting.
- Coverage is stated per roll after overlap allowance
- Apply 10% waste factor as standard estimating practice
- Always round rolls up to whole units
Memory trick: Add ten percent before you cut the roll.