Residential Building Inspector B1Roof-Ceiling ConstructionHard
An inspector is reviewing the design for a residential roof system that includes a valley. The plans specify the use of an open valley method for asphalt shingles. What is the minimum width required for the metal valley flashing at the top of the valley?
- A18 inches (457 mm)
- B24 inches (610 mm)
- C36 inches (914 mm)
- D12 inches (305 mm)
Show answer & explanationAnswer & explanation
Correct answer: B. 24 inches (610 mm)
For open valleys with asphalt shingles, the IRC requires metal valley flashing to have a minimum width of 24 inches (610 mm). This ensures adequate protection against water penetration in this critical area.
Why the other options are wrong
- A. 18 inches is not the minimum width specified by the IRC for this application.
- C. 36 inches would provide excellent coverage but is not the minimum required by code.
- D. 12 inches is too narrow for an open valley with asphalt shingles, increasing risk of leaks.
Open Valley Flashing Width
The minimum width of metal flashing required in an open valley to ensure proper water shedding and protection against leaks.
- Applies to open valley roof designs.
- Specific width for asphalt shingles is 24 inches.
- Ensures water flows freely down the valley without entering the roof structure.
Memory trick: Valleys need a wide shield, 24 inches is the minimum yield.