CSLB C-39 Roofing ContractorEstimating and PlanningHard
A roof has a 12-inch eave overhang and a 6-inch-thick exterior wall. Code requires the ice barrier to extend to a point at least 24 inches inside the interior wall face. The roof slope is 6:12. What is the minimum length of ice and water shield required, measured along the roof slope from the eave edge, rounded to the nearest tenth of a foot?
- A3.5 ft
- B5.0 ft
- C3.9 ft
- D4.5 ft
Show answer & explanationAnswer & explanation
Correct answer: C. 3.9 ft
Horizontal distance = 12 in overhang + 6 in wall + 24 in interior = 42 in = 3.5 ft. Slope factor for 6:12 = √(1+(6/12)²) = √1.25 = 1.118. Sloped length = 3.5 × 1.118 = 3.91 ft, rounding to 3.9 ft.
Why the other options are wrong
- A. This is the horizontal distance only, not accounting for slope.
- B. Significantly exceeds the correct sloped measurement.
- D. Overstates the calculated sloped distance.
Ice Barrier Slope Length
Ice and water shield length must be measured along the actual roof slope, not the flat horizontal distance, using the slope factor for accurate coverage.
- Add overhang + wall thickness + required interior distance for horizontal run
- Apply slope factor to convert horizontal distance to sloped length
- Code minimum is 24 inches inside interior wall face for most jurisdictions
Memory trick: Measure flat, then stretch it up the slope.