A valley gutter is the metal or lead channel that carries water down the internal angle where two roof slopes meet, then hands it off to the eaves gutter and downspout. It is the busiest drainage line on a pitched roof: two roof planes funnel their combined runoff into one narrow trough, so the valley gutter moves more water per foot than any other part of the roof. Get the metal, the width, and the laps right and it outlasts the shingles. Get them wrong and the valley is where most whole-roof leaks start.
This guide covers the valley gutter as a physical drainage component: what it is, the metals used, how wide it needs to be, how a lead valley gutter differs from a US open metal valley, and the exact points where valley gutters leak. For the shingle-integration side of the decision, our roof valley flashing details guide compares the open, woven, and closed-cut methods in full. This page stays on the gutter itself.
What is a valley gutter on a roof?
A valley gutter is the lined channel formed at a roof valley, the internal angle where two pitched roof planes intersect and shed water toward a single line. The lining, usually preformed metal or dressed lead, is what makes it a gutter rather than a raw seam. Water from both slopes collects in this trough and runs to the eaves. Because it concentrates the flow of two roof faces, the valley gutter is sized and detailed to handle roughly the combined runoff of both contributing areas.
Terminology varies by region. In North America the same detail is usually called an open metal valley or simply the valley flashing. In the UK, Ireland, and Australia the term valley gutter is standard, and the traditional version is a lead-lined channel over a timber valley board. Both describe the same job: a lined drainage channel at the meeting of two slopes. The difference is mostly in the material tradition and how the finish courses meet the metal.
Valley gutter vs eaves gutter: not the same thing
A valley gutter sits on the slope of the roof between two planes; an eaves gutter (the trough at the roof edge) sits horizontally along the fascia. The valley gutter feeds the eaves gutter, not the other way around. This matters for diagnosis: water overshooting or backing up at the eaves is a gutter problem, while staining below a valley higher up the roof points at the valley gutter lining or its laps. For the edge trough, see our seamless gutter cost per foot breakdown.
Valley gutter materials: which metal to use
Valley gutters are lined with galvanized steel, aluminum, stainless steel, copper, or lead, and the right choice depends on the roof covering, the local climate, and how long you want the valley to outlast a re-roof. The metal must resist corrosion from constant wetting and from any dissimilar metals it touches. A valley gutter that fails before the field shingles forces a partial tear-off, so most roofers spec the valley to match or exceed the roof’s service life.
The table below compares the common valley gutter metals on the properties that decide most jobs.
| Metal | Typical gauge / thickness | Service life | Best fit | Watch-out |
|---|---|---|---|---|
| Galvanized steel | 26 to 28 gauge | 15 to 30 years | Asphalt shingle roofs, budget open valleys | Rusts once the zinc coating wears; avoid contact with copper |
| Aluminum | 0.019 to 0.032 in | 25 to 40 years | Coastal and general residential | Softer, dents under falling debris and ladders |
| Stainless steel | 26 gauge | 40 to 75 years | Long-life and premium roofs | Higher cost; harder to form on site |
| Copper | 16 oz (0.0216 in) | 60 to 100+ years | Slate, tile, and heritage roofs | Runoff stains and can corrode aluminum and steel below it |
| Lead (code 4 to 5) | 1.8 to 2.24 mm | 60 to 100+ years | UK/tile/slate lead valley gutters | Long runs need expansion joints or it splits |
Two rules cut across the table. First, never mix metals that drive galvanic corrosion: copper runoff onto galvanized steel or aluminum will eat the cheaper metal, so keep the whole valley line to one metal family. Second, the code minimum for an open metal valley is usually 24 inches (610 mm) wide, 28-gauge or heavier, per common asphalt shingle manufacturer specs and IRC-based practice. Thinner or narrower and the valley oil-cans, rusts early, or overtops in heavy rain.
W-valley vs V-valley vs plain valley metal
A W-valley has a raised crimp (a small standing rib) formed down its center, while a V-valley or plain valley is a simple bent channel with no center rib. The W profile is the upgrade: the center rib acts as a water diverter, stopping runoff from one slope from shooting across the valley and up under the shingles on the opposite slope. On roofs where the two planes have different pitches, or in high-rain and heavy-snow regions, the W-valley is the safer default.
- W-valley: Center crimp diverts cross-flow and adds stiffness. Best for mismatched slopes, wide valleys, and heavy weather. Slightly higher cost and needs a matching starter cut on the shingles.
- V-valley (plain): Single bend to the valley angle, no rib. Cheaper and fine for equal-pitch slopes in moderate climates, but more prone to cross-wash on steep or unequal planes.
- Lead valley gutter (UK): Dressed over a timber valley board and tilting fillets, forming a wide flat-bottomed channel rather than a sharp V. Sized to the roof area it drains, often 300 mm or wider on the flat.
Valley gutter width and how to size it
Valley gutter width should never be less than 24 inches (610 mm) of metal for an open valley, and the exposed channel should widen as it runs downslope so the fast-moving water lower down never overtops the edges. A common rule is to spread the shingle cut lines about 6 inches apart at the ridge, then flare them roughly 1/8 inch per foot on each side as the valley descends. The steeper and longer the valley, the wider it should open at the bottom.
Lead and box-style valley gutters are sized differently, by the roof area they drain rather than a fixed strip. Larger contributing roof areas, low pitches, and heavy-rainfall regions all push the required channel width up. When two long slopes meet at a shallow angle, the valley behaves almost like a horizontal gutter and can need a genuine box-gutter design. For that case, see our box gutter guide on how they work, fail, and get repaired.
- Set the top width. Leave about 6 inches of exposed channel at the ridge for a standard shingle valley.
- Flare the sides. Widen the exposed channel roughly 1/8 inch per foot on each side moving downslope.
- Run the metal full length. Use continuous lengths where possible; where you must lap, overlap uphill piece over downhill by at least 6 inches, sealed and fastened only at the outer edges.
- Fasten outside the water line. Clip or nail only near the outer edges of the metal, never through the center channel, so no fastener sits in the flow path.
Where valley gutters leak (the failure points)
Most valley gutter leaks trace to four causes: fasteners driven through the water channel, laps run the wrong way or too short, debris and ice damming the trough, and corrosion or splitting of the metal itself. The valley concentrates flow, so a small defect that a flat field shingle would shrug off becomes an active leak here. Diagnosing which of the four is at work tells you whether it is a cheap reseal or a valley rebuild.
| Failure point | What you see | Cause | Fix |
|---|---|---|---|
| Fastener in the channel | Rust weep or stain at a nail line mid-valley | Nailed through the flow path instead of the edges | Reseat fasteners to the outer edges, seal the old holes |
| Reverse or short lap | Leak at a horizontal seam after rain | Downhill piece lapped over uphill, or lap under 6 in | Re-lap uphill over downhill, minimum 6 in, seal edges |
| Debris or ice dam | Overflow onto adjacent shingles, backup stains | Leaves, granules, or ice blocking the trough | Clear the valley; add self-adhered membrane and widen channel |
| Corrosion or split | Pinholes, rust-through, cracked lead | Worn galvanizing, galvanic contact, or thermal fatigue | Replace the valley metal; add expansion joints on long lead runs |
Underneath every open metal valley there should be a course of self-adhered ice-and-water membrane, at least 36 inches wide, running the full length of the valley before the metal goes down. This is the backup layer: if the metal is ever breached, the membrane keeps the deck dry. On a re-roof, a valley that leaks despite intact metal almost always has a missing or failed membrane below it. For tracing a leak that has already reached the interior, our asphalt shingle roof leak repair guide walks the diagnosis by source.
Open valley gutter vs closed valley: the short version
An open valley leaves the metal channel exposed down the center, while a closed valley (woven or closed-cut) runs shingles across or up to the valley so no metal shows. Open metal valleys shed water, ice, and debris fastest and are the most durable, which is why they are the recommended detail for steep-slope and heavy-weather roofs. Closed valleys look cleaner and install faster but hide the flashing, so a hidden defect can leak unseen.
Because this page is about the valley gutter as a drainage component, the full method comparison lives elsewhere. Read our roof valley flashing details guide for the open vs woven vs closed-cut breakdown, warranty implications, and which method suits your shingle type. In short: choose an open metal valley gutter when durability and water handling matter most, and a closed valley when appearance and speed win and the roof is a moderate climate.
How a valley gutter connects to the rest of the roof drainage
A valley gutter is one link in the roof’s drainage chain: roof planes feed the valley, the valley feeds the eaves gutter, and the eaves gutter feeds the downspouts. A weak link anywhere backs water up into the ones above it. An undersized downspout can cause the eaves gutter to overflow, which can push water back toward the valley outlet in extreme rain, so valley problems are sometimes really capacity problems downstream.
When you replace or upgrade a valley gutter, check that the eaves gutter below it is sloped and sized to take the concentrated discharge. A valley dumps a lot of water into a short length of eaves gutter, so that section may need a larger outlet or an extra downspout. Match the valley metal to the roof covering’s expected life so you are not tearing shingles off in ten years to swap a rusted-out channel.
Frequently asked questions
What is a valley gutter?
A valley gutter is the metal or lead lined channel at a roof valley, the internal angle where two pitched roof slopes meet. It collects the combined runoff from both slopes and carries it down to the eaves gutter and downspout. Because it handles the water of two roof faces in one narrow trough, it is the highest-flow drainage line on a pitched roof and is sized and lined accordingly.
What is the best metal for a valley gutter?
Galvanized steel and aluminum are the common residential choices, copper and lead are used on slate, tile, and heritage roofs, and stainless steel suits long-life roofs. The key rule is to keep the whole valley to one metal family, since copper runoff corrodes aluminum and steel below it. Match the metal’s service life to the roof covering so the valley does not fail before the shingles.
How wide should a valley gutter be?
An open metal valley uses at least 24 inches (610 mm) of metal, with the exposed channel typically starting about 6 inches wide at the ridge and flaring roughly 1/8 inch per foot on each side as it descends. Steeper, longer valleys and high-rainfall areas need wider channels. Lead and box valley gutters are sized by the roof area they drain rather than a fixed strip width.
Why does my valley gutter leak?
The four usual causes are fasteners driven through the water channel, laps run reverse or too short, debris or ice damming the trough, and corrosion or splitting of the metal. The valley concentrates flow, so small defects that a flat shingle would shrug off leak here. A self-adhered ice-and-water membrane at least 36 inches wide should sit under the metal as a backup layer.
What is the difference between an open and closed valley gutter?
An open valley leaves the metal channel exposed down the center, so it sheds ice, water, and debris fastest and lasts longest. A closed valley runs shingles across (woven) or up to (closed-cut) the valley so no metal shows, which looks cleaner and installs faster but hides the flashing. Open metal valleys are the recommended detail for steep-slope and heavy-weather roofs.
Is a valley gutter the same as a roof gutter?
No. A valley gutter runs on the roof slope between two planes and drains into the eaves gutter. The eaves gutter (the roof gutter people usually mean) sits horizontally along the fascia at the roof edge. The valley feeds the eaves gutter, not the reverse, so a leak below a valley higher on the roof is a valley problem, not an eaves gutter problem.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.