CSLB C-39 Roofing ContractorFlashing, Ventilation and InsulationEasy
A roofing crew is installing an open valley on a composition shingle roof. Per code, what is the minimum overall width of the sheet metal valley flashing (measured across the valley centerline)?
- A18 inches
- B36 inches
- C24 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 24 inches
Code requires open valley metal flashing to extend at least 12 inches on each side of the valley centerline, for a total minimum width of 24 inches. This ensures adequate coverage to shed concentrated water flow in the valley.
Why the other options are wrong
- A. Still short of the 12-inch-per-side minimum on both sides.
- B. Exceeds code minimum; not required though not prohibited.
- D. Too narrow to provide the required 12 inches of coverage on each side.
Open Valley Flashing Width
Sheet metal valley flashing must extend a minimum of 12 inches on each side of the valley centerline, totaling 24 inches minimum width.
- Open valleys concentrate the most water flow on a roof.
- Minimum metal width is 24 inches total (12 in. each side).
- Metal must be corrosion-resistant, commonly 26-gauge galvanized or better.
Memory trick: 'Twelve and twelve makes a valley safe from twenty-four.'