CSLB C-39 Roofing ContractorLow-Slope RoofingHard
A ballasted EPDM roof system is being installed in a low wind exposure zone where code requires a minimum ballast rate of 10 lb per square foot. The roof area is 6,000 sq ft. How many tons of ballast are required?
- A20 tons
- B30 tons
- C40 tons
- D15 tons
Show answer & explanationAnswer & explanation
Correct answer: B. 30 tons
6,000 sq ft × 10 lb/sq ft = 60,000 lb. Converting to tons: 60,000 ÷ 2,000 lb/ton = 30 tons of ballast required.
Why the other options are wrong
- A. This does not match the correct multiplication and conversion.
- C. This overstates the required ballast weight.
- D. This underestimates the total ballast weight required.
Ballast Weight Calculation
The total weight of loose ballast (typically river rock) required on a ballasted single-ply roof, calculated by multiplying roof area by the code-required ballast rate per square foot.
- Common minimum rate: 10 lb/sq ft in low wind zones
- Higher wind exposure zones require heavier ballast rates
- 1 ton = 2,000 lb
Memory trick: Area times rate, then split by two-thousand for the weight.