CSLB C-39 Roofing ContractorSteep-Slope RoofingMedium
A roofer is preparing to install a new open metal valley on an asphalt shingle roof. To ensure adequate drainage and prevent water from splashing onto the underlayment, what is the minimum recommended width of the open portion of the valley at the top, where it typically narrows?
- A4 inches
- B2 inches
- C6 inches
- D8 inches
Show answer & explanationAnswer & explanation
Correct answer: A. 4 inches
For open metal valleys, the general recommendation is that the valley should be at least 4 inches wide at the top and gradually widen by 1/8 to 3/16 inch per foot down the valley. This minimum width ensures proper water flow and prevents ice or debris buildup.
Why the other options are wrong
- B. 2 inches is too narrow for an open valley, increasing the risk of debris buildup and water overflow.
- C. 6 inches is a common width for valleys, but 4 inches is the minimum acceptable width at the top.
- D. 8 inches is unnecessarily wide for the top of an open valley and would reduce the aesthetic appeal without significant functional benefit.
Open Metal Valley Width
The width of the exposed metal flashing in an open valley, critical for drainage and preventing water intrusion.
- Widens from top to bottom.
- Prevents debris and ice dams.
- Ensures proper water shedding.
Memory trick: Four inches at the top, so water will never stop.