Roof valleys: where two slopes meet and the water goes
A valley is the inside corner where two roof slopes meet. It carries more water than any other part of the roof, so how it is built matters.
Look at a roof where two slopes come together and make a V that points down. That inside corner is a valley. The outside corner, where slopes meet at the top, is a hip or a ridge.
Rain from both slopes runs into the valley. So the valley carries the water of two roof sections in one narrow line. A bad valley is one of the most common places a roof leaks.
The three ways to build a valley
| Valley | How it is built | Good to know |
|---|---|---|
| Open valley | Metal runs down the center. Shingles stop short on both sides, so you see the metal. | Moves water fast. The metal must not rust, and it costs more to install. |
| Closed-cut valley | Shingles from one slope run across the valley. Shingles from the other slope are cut in a straight line along it. | A clean look and common with architectural shingles. |
| Woven valley | Shingles from both slopes overlap each other across the valley. | Works with flat 3-tab shingles. Thick architectural shingles do not weave well. |
Shingle makers set which valley types their warranty allows. Ask your roofer which one they will use and why.
What the building code asks for
For asphalt shingles, the International Residential Code covers valleys in section R905.2.8.2. Every valley needs a lining under the shingles. For an open valley lined with metal, the code calls for corrosion-resistant metal at least 24 inches wide.
Where ice dams are common, section R905.1.2 also calls for an ice barrier at the roof edge. Many roofers also put self-sealing ice and water membrane down the full valley. Ask if it is in your quote.
Signs a valley is leaking
Check for these
- Leaves and debris sitting in the valley Debris holds water and slows it down. Clean valleys drain.
- Shingles that are cracked, loose or missing along the valley line Water runs hardest here, so small damage turns into a leak fast.
- Nails close to the center of the valley Nails in the middle of a valley are a known installation error. Water runs right over them.
- A ceiling or attic stain below where two slopes meet Valley leaks show up inside below the valley line, often after heavy rain.
Have a roofer check your valleys
Tell us your city and what you see. We match you with local roofing contractors, and you make the calls yourself.
Get matched with a roofer See the parts of a roofSources
International Code Council, 2021 International Residential Code, Chapter 9, sections R905.1.2 (ice barrier) and R905.2.8.2 (valleys): codes.iccsafe.org.
Questions homeowners actually ask
What is a valley on a roof?
A valley is the inside corner where two roof slopes meet. It carries the rain from both slopes.
Which is better, an open or a closed valley?
Both work when they are built right. Open metal valleys move water fast. Closed-cut valleys look cleaner and are common with architectural shingles. Follow what the shingle maker allows.
Can a roof valley be repaired without a new roof?
Often, yes. A roofer can take up the shingles along the valley, replace the lining, and put the valley back. It is a bigger job than a patch, but smaller than a new roof.