Roof valley flashing is the metal or membrane lining in the V where two roof slopes meet. It carries the runoff from both slopes down to the gutter, so it takes more water than any other part of your roof. A valley built with the right layers can last as long as the shingles around it. A valley built with thin metal, no membrane or poorly placed nails is where most leaks start. Below you will find the valley types, what proper flashing looks like, the signs of failure, and the practical next steps if you think yours is leaking.
TL;DR
- A valley is the most water-loaded spot on a roof. Building scientists describe the concentrated runoff as what makes valleys so vulnerable.
- Open valleys show metal. Closed valleys hide it under shingles. Both need a self-adhering membrane underneath and correct integration with the underlayment.
- Look for stains on ceilings under the valley line, shingle granules piled at the bottom of the valley, rust, and lifted or cut shingle edges.
- A valley repair is often local, but a failed valley on an old roof can point to a bigger problem. Get the whole roof looked at before you pay for a patch.
- Ask any roofer which valley method, metal gauge and membrane they will use, and get that in writing.
Table of Contents
- What a roof valley is and why it leaks first
- Roof valley types: open, closed and woven
- Open vs. closed valley: which is better?
- What proper valley flashing looks like
- Signs of a leaking roof valley
- Roof valley leak repair: what is realistic
- Our perspective: what we look at first on a valley
- Questions to ask a roofer about valleys
- Valley damage after a Texas storm
- Help with your valley, repair or replacement
- Related details that fail with valleys
- FAQ
- Sources
What a roof valley is and why it leaks first
A valley is the internal angle formed where two sloping roof planes meet. Think of an L-shaped house or a dormer: every inside corner of the roofline is a valley. Rain from each slope runs into that channel, and the water speeds up as it goes. The Building America Solution Center notes that this concentrated flow is why valleys need specialized flashing, usually metal or self-adhering membrane.
The shingle field itself rarely fails first. Fine Homebuilding makes the same point: roofs leak at connections, such as where one roof plane meets another, a wall, or a penetration, far more often than in the open field unless there is damage or very poor installation.
There is also a mechanism worth knowing. Water coming off a steep slope can shoot across the valley centerline and push under the shingles on the opposite side. InterNACHI describes this kind of cross-flow, and installers counter it with valley metal that has a center rib, crimp or W profile, which breaks the flow mechanically before it travels sideways.
Roof valley types: open, closed and woven
Most homeowners meet three valley styles. Which one you have affects how it looks, how you inspect it and how it is repaired.
Open valley
In an open valley, metal flashing stays visible down the center, and the shingles on each side are cut back from the centerline. InterNACHI gives the typical setback as 2 to 6 inches from the centerline. Because the metal is exposed, you can see its condition from the ground with binoculars or from a ladder at the eave, and water has a clear, smooth path.
Closed valley
In a closed valley, shingles run continuously across the valley and cover the lining below. It looks cleaner from the street. The tradeoff is that you cannot see what is underneath, so a problem can go unnoticed until a stain shows up inside. Closed-cut valleys, where one slope's shingles run across and the other side is trimmed along the line, are the common version.
Woven valley
A woven valley interlaces shingles from both slopes across the valley. It is a closed valley too, and it is mostly used with certain shingle types. Many manufacturers and installers prefer a cut or open method on steeper or high-runoff roofs, so follow the shingle maker's instructions for the product on your roof.
Metal roofs
On standing seam and other metal roofs, valleys are formed from metal panels and trim. Detail quality matters just as much there. For a view of how trim and flashing connections are specified on metal systems, see this guide to sidewall flashing on standing seam roofs, which covers a related flashing connection.
Open vs. closed valley: which is better?
Neither is automatically better. Both work when built correctly.
| Factor | Open valley | Closed valley |
|---|---|---|
| Appearance | Metal line visible down the roof | Shingles run through, flashing hidden |
| Water handling | Smooth metal sheds heavy flow well | Relies on membrane and shingle overlap |
| Inspection | Easy to see rust, dents, debris | Hard to see, signs show up late |
| Debris | Leaves can pile on the metal, but are easy to clear | Debris and granules can hide in the shingle layer |
| Typical concern | Nail placement, metal gauge, sealed edges | Membrane quality, shingle trimming, overlap |
We lean toward open metal valleys for homes with heavy tree cover or steep slopes that shed a lot of water at speed, because you can see them and service them. For a clean look on a simple roof, a properly built closed valley is fine. What matters more than the style is the layers beneath it.
What proper valley flashing looks like
A code-minimum valley and a good valley are not the same thing, and building science sources agree on the basic stack.
The layers, bottom to top
- Clean, dry, solid roof deck. Rotted or soft decking has to be replaced first. Flashing cannot fix a bad base.
- Self-adhering membrane (peel-and-stick). The Building Science Education site says to install a self-sealing bituminous membrane on the roof sheathing under the metal and shingles. Work from the low point to the high point, with end laps of at least 6 inches in shingle fashion, so water runs over the joints rather than into them. The same guidance points to a membrane centered on the valley and at least 36 inches wide.
- Underlayment integrated with the membrane. Lapping is done so water always sheds downhill.
- Metal valley flashing (open valleys). The same source calls for metal at least 24 inches wide and no lighter than 26-gauge. The 2018 International Residential Code excerpt reproduced by one Missouri city says open metal valley linings must be not less than 24 inches wide and made of approved corrosion-resistant metal.
- Shingles, trimmed and sealed correctly. For open valleys, shingles are held back from the centerline, and the cut edges are usually clipped at the top corner so water does not get driven under them.
Slope, material and the manufacturer
Code sets minimums. Roofing materials differ, and the manufacturer's instructions often go beyond base code, which also matters for keeping a product warranty. Even within one material the details change: wood shingle guidance from the Cedar Shake and Shingle Bureau, for example, calls for valley flashing to extend at least 8 inches each side of the centerline on slopes of 12:12 or steeper, with different figures on lower slopes. Local code can differ again, so a roofer working in your area should know which edition applies to you.
Nails
Nails through the valley metal are a common shortcut that causes trouble. GAF's technical bulletin on nailing metal flashing in open valleys addresses where to fasten the edges of the metal, because a nail head or shaft in the water channel is a puncture waiting to leak. The rule of thumb: fasteners go near the outer edges, never in the center where water runs.
Signs of a leaking roof valley
A leaking roof valley rarely announces itself with a drip right under it. Water travels along the deck and rafters first. Check for:
- Ceiling or wall stains along a line that matches a valley on the roof above. Brown rings that grow after rain are a classic sign.
- Granules collecting at the bottom of the valley or in the gutter below it, which suggests heavy wear in the channel.
- Rust, pinholes or dents in exposed metal in an open valley.
- Lifted, curled or cracked shingles along the valley edges.
- Debris dams such as leaves, branches or moss that force water sideways under shingles.
- Sagging or soft spots on the roof surface, which can mean the deck below has already taken on water.
- Musty smells or visible mold in the attic below the valley.
Start from the ground. Our roof inspection checklist walks through five checks you can do without climbing. If you do go into the attic, look at the underside of the deck below each valley with a flashlight after a rain. Stay off steep or wet roofs. Falls from roofs are a real danger, and a professional inspection is safer than a DIY climb.
Flashing problems do not stop at valleys. If your stain is near a chimney, read about four causes of roof leaks around a chimney before you assume the valley is the culprit.
Roof valley leak repair: what is realistic
How a valley gets repaired depends on what failed.
Small, local failure. A nail pop, a short section of damaged shingle edge or a small puncture can sometimes be fixed by replacing shingles, resealing and patching the metal or membrane. That is a repair, not a bandage of roofing cement.
Failed flashing along a section. The shingles along the valley are pulled back, the old flashing and membrane removed, the deck checked, and a new membrane and metal lining installed with the shingles re-integrated. This is more involved, but it is a real fix.
Widespread failure on an old roof. If the shingles are brittle, granules are gone and several areas are leaking, repairing the valley alone may not hold. Our 30% rule for repair or replace lays out how Central Texas homeowners can judge it.
A word of caution about tar. Smearing roof cement over a valley hides a problem for a season and can trap moisture. If a contractor's only answer is a tube of sealant, get a second opinion.
Why does this matter beyond a stain? InterNACHI warns that poor valley work, such as light-gauge metal or leaving out ice and water shield, will almost certainly lead to leaks, and that leaks can turn into mold and rot that moves into ceilings and wall framing. Fixing it early is cheaper than fixing the framing.
Our perspective: what we look at first on a valley
We work on roofs across Central Texas, and when a homeowner calls about a leak, the valleys are one of the first places we check, along with chimneys, walls and penetrations. Our view is simple: the shingle is rarely the problem. The connection is.
Here is how we think about it:
- The membrane is the backup you never see. A good valley has a second layer of defense under the metal. That is the part cheap bids tend to skip, and it is the part you cannot judge once the shingles are on.
- Match the valley to the roof. Tree cover, slope and shingle type all push us toward open or closed. We would rather explain why than just give you a style.
- Do not repair what you cannot price against a replacement. If the roof is near the end of its life, we will say so and show you both options.
- Get more than one estimate. We tell homeowners to compare multiple bids. Ask each contractor the same questions about valley method, metal gauge and underlayment, and compare the answers, not just the totals.
- Storm damage is a separate conversation. If hail or wind caused the damage, the insurance process matters as much as the repair itself.
— Dan
Questions to ask a roofer about valleys
Whether you hire us or someone else, these questions separate a thought-out valley from a rushed one:
- Will the valleys be open or closed, and why for my roof?
- What is under the metal? Is it a self-adhering membrane, and how wide?
- What metal and gauge will you use, and how wide is it?
- Where do the nails go, and will any penetrate the water channel?
- Will you follow the shingle manufacturer's valley instructions so the warranty stays intact?
- Will you check and replace damaged decking in the valley before flashing?
- Is the valley detail written in the estimate?
If answers are vague, that tells you how the valley will be built.
Valley damage after a Texas storm
Hail and wind can dent valley metal, crack shingle edges and loosen the seals that keep water out. Damage is easy to miss from the ground, especially on closed valleys. If a storm has passed and you see new stains inside, or your neighbors are getting inspections, have the roof checked before the next rain.
Two of our guides help here. Don't ignore small hail explains when a hail inspection is worth it, and our storm damage inspection guide covers photos and getting three bids to support a claim. Photograph the damage and the interior stains with dates before any temporary repair, and keep receipts for emergency tarping.
Help with your valley, repair or replacement
If you suspect a leaking valley, we offer inspections and free estimates for homeowners in Central Texas, from small roofing repairs to full replacements. If a storm is involved, we can guide you through the claim process on our insurance claims page. We back our pricing with a Best Price Guarantee, and we encourage you to get other estimates to compare. You can start at budgetroofingandsiding.com.
Related details that fail with valleys
A valley is one of several transitions that need careful flashing. If you are fixing one, look at the others at the same time:
- Eaves and rakes: a drip edge directs water into the gutter instead of behind it.
- Roof-to-wall joints and chimneys: step flashing and counterflashing that fail show up as stains in the same places.
- Ventilation openings: compare options in our guide to ridge vents and turbines.
- Fascia and soffit: water that gets past a valley end often reaches these first. See our fascia and soffit repair guide.
The Building Science Education site frames it well: a roof works best as a water-managed assembly where membrane and metal work together in strategic places, not as a single piece of metal.
FAQ
Does flashing go under or over shingles?
It depends on the type. In a closed valley the lining sits under the shingles. In an open valley the metal is laid on the membrane and the shingles on each side lap over its edges, held back from the centerline. Flashing is always lapped so water runs over each joint in the downhill direction.
How wide should valley flashing be?
For open metal valleys, the 2018 IRC excerpt cited above sets a minimum of 24 inches wide. Building science guidance also recommends at least 26-gauge metal and a membrane that is at least 36 inches wide under it. Your shingle maker's instructions may ask for more, so check them.
Can I fix a leaking roof valley myself?
Sealing a valley with roof cement rarely lasts and can hide the real source. A proper repair means lifting shingles, checking the deck and rebuilding the layers, which is work on a sloped roof where falls are a danger. For a leak, call a roofer to inspect it first.
How long does valley flashing last?
There is no single number. Life depends on the metal, the membrane beneath it, tree debris, storms and the quality of installation. Properly built valleys are meant to last with the roof, so a failure early in a roof's life usually points to a workmanship or material problem.
What is the most common cause of a roof valley leak?
The usual causes are thin or damaged metal, missing membrane underneath, nails in the water channel and water forced under shingles from the opposite slope. Debris and storm damage add to the load. An inspection can tell you which applies to your roof.
Sources
- Roof Valleys and Penetrations Sealed, Building America Solution Center
- Sealing Roof Valleys, Building Science Education
- Water-managed Roof Assembly, Building Science Education
- Mastering Roof Inspections: Flashing, Part 5, InterNACHI
- Critical Roof Flashings Keep Water Out, Fine Homebuilding
- 2018 IRC Section R905 Requirements for Roof Coverings (excerpt)
- Nailing Metal Flashing in Open Valleys, GAF technical bulletin
- Flashing Details for Shake and Shingle Valleys, Cedar Shake and Shingle Bureau