Know Your Roof · Flashing & Roof Edge
Roof Valley and Valley Flashing
Quick answer
A roof valley is the inside angle where two roof slopes meet. A lot of the roof's runoff ends up there, so it's lined with valley flashing, which is metal or waterproof membrane under the shingles. A failed valley is one of the more common sources of leaks.
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Why valleys matter
Water from both slopes funnels into the valley, so it handles more water, moving faster, than any other part of the roof. Leaves and debris collect there, and ice can build up in winter.
Types of valleys
| Type | How it looks | Notes |
|---|---|---|
| Open valley | Metal shows down the center, shingles cut back on each side | Sheds water and debris well |
| Closed-cut valley | Shingles cover the valley, one side cut and trimmed | Cleaner look, common on shingle roofs |
| Woven valley | Shingles from both slopes are interlaced | Used on some asphalt shingle jobs |
The best choice depends on the roof, the shingle and the manufacturer's instructions.
Valley flashing materials
Galvanized steel and aluminum are common, usually formed in a V or W shape. A W-shaped valley has a center rib that slows fast water. Waterproof membrane goes under closed valleys.
Signs of valley problems
Rust, holes or lifted metal. Cracked or worn shingles along the valley. Debris piling up. Stains on the ceiling under a valley line.
What does valley flashing repair cost?
A leaking valley is one of the most common repair calls. Flashing repair around a wall, chimney, or valley typically runs $400 to $900. A minor repair that includes flashing, a vent boot, or one or two shingles runs $400 to $750. The final number depends on how much flashing is damaged and how hard it is to reach, and every job starts with a free roof inspection.
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