CSLB C-39 Roofing ContractorSteep-Slope RoofingMedium
A contractor is installing 20-inch slate shingles on a roof with an 8:12 slope, which requires a 3-inch headlap. Using the standard slate exposure formula, what exposure should be used?
- A10 inches
- B6.5 inches
- C8.5 inches
- D7 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 8.5 inches
Slate exposure is calculated as (Length - Headlap) / 2 = (20 - 3) / 2 = 8.5 inches. This formula accounts for double-coverage installation where each slate overlaps two courses below it.
Why the other options are wrong
- A. 10 inches would leave insufficient headlap for proper double coverage.
- B. 6.5 inches would result from using a different headlap value, not 3 inches.
- D. 7 inches does not match the required formula calculation.
Slate Exposure Formula
Exposure = (Slate Length - Headlap) / 2, used to determine coursing on double-coverage slate roofs.
- Headlap varies by slope: 3in for steeper, 4in for lower slopes
- Formula ensures double-coverage weatherproofing
- Steeper slopes allow less headlap and more exposure
Memory trick: Length minus lap, then split in half.