Roof valley leaks happen when the water pouring off two roof planes finds a gap, and the right repair depends on what is under the shingles. The usual causes: a lining that is missing or too narrow, nails driven too close to the valley’s center line, cut shingle edges that were never trimmed back or sealed, or debris and ice holding water in the channel. Because a valley carries so much water, a small installation shortcut there shows up as a ceiling stain long before the rest of the roof wears out. This page is general information; your roofer and building department make the final call.
On this page: Signs · Valley types · Causes · What to check · Repairs · Code basis · When to call
Signs of a leaking valley
- A ceiling stain roughly below where two roof slopes meet.
- Water that appears only in heavy rain or fast snowmelt.
- In the attic, dark streaks along the valley rafter or wet sheathing on both sides of it.
- From outside, piles of needles or leaves in the valley, curled or lifted shingle edges, or ice that lingers in the valley after the rest of the roof has cleared.
Open and closed valleys
| Type | What you see | Main weak points |
|---|---|---|
| Open metal valley | A strip of exposed metal down the center | Lining width, fasteners in the metal, shingle edges not set in cement |
| Closed-cut valley | Shingles from one side run across; the other side is cut in a straight line | Nails too near the center, cut line too close, cut edges not sealed |
| Woven valley | Shingles from both sides overlap in a woven pattern | Nails too near the center line |
Why valleys leak
- No lining, or one that is too narrow, so water that gets past the shingles has nowhere safe to go.
- Fasteners too close to the center line. Every nail there is a hole in the busiest part of the roof.
- The cut side not trimmed back from the center or not sealed, so water runs under the cut edge.
- Debris and ice dams that back water up under the shingles. Pine needles are a common culprit in foothill and forested neighborhoods.
- Patching on top of an earlier valley repair without fixing what is underneath.
What you can check
- From the ground, use binoculars to look for debris, lifted or curled edges, and exposed nail heads in the valley.
- In the attic, look along the valley rafter after a heavy rain for staining or wet sheathing.
- Keep a log. Note whether the leak follows downpours, snowmelt, or both, and how long after the storm it starts.
Please do not walk a valley; it is the slickest, steepest part of most roofs.
Repair or rebuild
| Step | When it fits |
|---|---|
| Clear debris and reseal the cut edges | Valley lining is in place; edges are lifted or debris is backing water up. |
| Strip and relay the valley with full-width lining | Lining missing or too narrow, or nails in the center zone. |
| Replace soft decking along the valley | Sheathing is spongy or stained through. |
| Full reroof | The field shingles are also at the end of their life. |
Fixes that do not work: running caulk down the valley, nailing through the valley center, and adding a top layer of shingles or metal without fixing the lining beneath.
Code and manufacturer basis
The 2024 IRC, section R905.2.8.2, requires valley linings to go on before the shingles. Open metal valleys need lining at least 24 inches wide. Closed valleys can use a 36-inch-wide ply of smooth roll roofing, a 36-inch self-adhering membrane, or one of the open-valley linings. Owens Corning’s Duration instructions for closed-cut valleys call for a 36-inch liner, shingles from one side carried at least 12 inches across the center line, fasteners at least 6 inches from the center line, and a cut line 2 inches from the center on the unshingled side.
IBHS’s FORTIFIED technical bulletin on shingle details goes further for high-wind homes: shingles on both sides of an open valley set in an 8-inch strip of flashing cement, and the cut side of a closed valley set in a 2-inch strip. Our standard valley detail meets the code where we work; ask your roofer to describe theirs in writing.
When to call a roofer
Call if you see a stain near a valley, edges lifting, or debris that keeps coming back. Valleys are a common place for snow and ice to sit through a Colorado cold spell, so a weak valley often shows up in late winter. If the leak only shows up in winter, read about attic frost and our existing guide to ice dams as well. For leaks along walls rather than valleys, see roof-to-wall flashing. The roof problems guide covers the rest.
Ask us to look at your valleys
Integrity Roofing and Painting is veteran-owned and family-run since 1990, an Owens Corning Platinum Preferred contractor with 650+ Google reviews. We check valley lining and fastener placement and give you photos, so you can see whether a repair will hold. Colorado Springs area: (719) 488-2800, free inspection. Denver metro: (303) 209-0152, free Denver inspection. Austin: (512) 610-5897, free Austin inspection. We get back to you the same business day.
Sources: 2024 IRC Chapter 9, section R905.2.8.2 (UpCodes); Owens Corning Duration installation instructions (valleys); IBHS FORTIFIED technical bulletin 2016-05.
