Why Valleys Are High-Risk Areas
A roof valley is where two roof slopes meet at an interior angle, forming a channel. Every raindrop that falls on either adjacent slope eventually flows to the valley. This concentrated water flow creates:
- Higher water volume and velocity than the field of the roof
- More debris accumulation — leaves and organic material funnel into valleys
- Accelerated wear on whatever waterproofing is there
- Ice dam risk at the bottom of valleys in cold climates
Valleys account for a disproportionate share of roof leaks relative to their area.
Types of Valley Installation
- Open valley (metal flashing): A strip of metal — typically aluminum or copper — runs the length of the valley. Shingles on both sides are cut to a straight line several inches back from the center, leaving the metal exposed. Water flows freely over the metal. The most durable option and easiest to inspect.
- Closed-cut valley: Shingles from one slope extend across the valley; shingles from the other slope are cut to a line over the valley. Underlayment and ice and water shield provide the waterproofing beneath. More common in residential re-roofing; depends heavily on proper underlayment installation.
- Woven valley: Shingles from both slopes alternate across the valley, woven together. Requires careful installation. Less common today due to difficulty getting a consistent, tight weave.
Signs of Valley Flashing Failure
- Water staining on ceilings in rooms below a valley
- Visible rust or corrosion on metal valley flashing
- Shingles lifting or pulling away from the valley centerline
- Moss or algae growth in the valley indicating persistent moisture
- Debris accumulation in open valleys that has not been cleared
- Lifted or cracked shingles adjacent to the valley
Related: How to Find a Roof Leak
Valley Repair vs. Replacement
Minor issues can sometimes be addressed with targeted repairs:
- Small rust spots or pinhole corrosion in metal flashing can be patched with roofing cement and a metal patch
- Seam separations in metal flashing can be re-sealed
- Lifted shingles adjacent to a valley can be re-secured
When to replace rather than repair:
- Metal flashing with widespread rust or corrosion
- Valley underlayment that has failed (requires removing shingles to access)
- Repeated leaks in the same valley location despite previous repairs
- Full roof replacement — valleys should always be re-flashed during a reroof
Frequently Asked Questions
Why do roof valleys leak?
Valleys concentrate water from two slopes into a single channel. High water volume accelerates wear, and debris accumulates there holding moisture. Common failures: corroded metal flashing, failed closed-cut underlayment, or debris-caused pooling.
What are the types of roof valley installation?
Open valleys (visible metal flashing, most durable), closed-cut valleys (shingles cover the valley, relying on underlayment), and woven valleys (shingles interleaved). Open valleys with metal flashing are easiest to inspect and repair.
How much does valley flashing repair cost?
Minor repairs: $150-$400. Significant re-flashing with shingle removal: $400-$1,000. Full valley re-flashing with shingle replacement: $800-$2,500+ for longer valleys.
Get a Valley Inspection
This page is for general informational purposes only. Valley repair complexity varies by installation type and damage extent. Consult a licensed roofing contractor for an assessment of your specific valley condition.