CSLB C-39 Roofing ContractorSteep-Slope RoofingMedium
A roofer is installing an open metal valley flashing on a composition shingle roof. To ensure proper water flow and prevent debris accumulation, what is the minimum recommended width of the exposed metal valley, measured at its narrowest point (top of the valley)?
- A4 inches
- B8 inches
- C6 inches
- D10 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 6 inches
For open metal valleys, the minimum exposed width at the top of the valley is typically 6 inches. This width allows for adequate water flow, prevents debris buildup, and reduces the chance of shingle blockage, especially as the valley widens towards the eaves.
Why the other options are wrong
- A. 4 inches is generally too narrow for an exposed open valley, increasing the risk of clogs and water overflow.
- B. 8 inches is a good width for valleys, especially longer ones, but is not the *minimum* required at the top.
- D. 10 inches would provide excellent drainage but is usually excessive for the minimum at the top of the valley.
Open Valley Flashing Width
The exposed width of an open metal valley is the visible portion of the metal flashing where two roof planes meet, designed to channel water efficiently.
- Width prevents water from directly contacting shingles in the valley.
- Narrowest at the top, widening towards the eave (tapered).
- Minimum width ensures adequate flow and debris resistance.
Memory trick: Valley's top, six inches stop, for water's hop.