Metal valleys are one of the highest-volume water paths on a shingle roof. Every roof plane that drains into a valley concentrates runoff into that line, which makes the valley detail more important than most homeowners realize.

The practical answer

A clean metal valley uses the right valley profile, proper underlayment beneath it, correct fastening outside the water path, straight shingle cuts, and enough metal exposure to move water without forcing it under the shingles.

W-valleyPreferred open profile
26 gaugeCommon upgraded metal
Open cutClean water path

What a metal valley actually does

A roof valley is where two sloped roof planes meet. Instead of water draining straight down one flat roof face, water from both sides collects in one channel. During heavy rain, melting snow, freeze-thaw cycles, or debris buildup, that channel carries more water than the surrounding roof field.

The metal valley creates a controlled drainage path. It gives water a smoother, more durable surface than exposed shingles alone and helps protect the valley line from wear, granule loss, and repeated water concentration.

The valley is not just a visual line on the roof. It is one of the main drainage details in the entire roofing system. West Country Roofing

Open valleys versus closed valleys

There are several ways to finish a shingle roof valley. The two broad categories are open valleys and closed valleys. In an open valley, metal remains visible between the shingle cuts. In a closed valley, shingles cover the valley surface and the drainage line is hidden beneath the shingle layout.

Valley styleHow it worksBest useWatch-outs
Open metal valleyShingles are cut back from the centre and the metal remains visible.Good water control, clean drainage, strong visual definition, and easier inspection.Requires straight cuts, careful layout, and metal that looks clean from the ground.
Closed-cut valleyOne side runs through and the opposite side is cut over it.Can look subtle when installed correctly and when product instructions allow it.More shingle material sits in the water path and workmanship matters heavily.
Woven valleyShingles from each side are woven through the valley.Limited use depending on shingle type and manufacturer instructions.Often not ideal for laminated shingles because it can create bulk and stress.

Why W-valley metal is commonly preferred

W-valley metal has a raised rib through the centre. That centre diverter helps slow cross-wash from one roof plane to the other and gives the valley a more defined drainage path. It also adds stiffness to the metal, which helps the valley sit cleaner and resist oil-canning compared with a completely flat piece.

For many shingle roofs, a properly installed open W-valley is the cleanest balance of performance, inspectability, and appearance. It is not complicated-looking from the ground, but it solves a difficult water-control problem at one of the roof’s busiest drainage points.

Centre rib

Helps separate the two drainage planes and reduce water washing across the valley centre.

Open exposure

Keeps the main water path on metal instead of forcing water over exposed shingle edges.

Cleaner serviceability

Open metal valleys are easier to see, inspect, clean, and understand later.

Better visual line

When the cuts are straight, the valley gives the roof a deliberate, finished look.

Gauge, coating, and durability

Metal gauge matters because valleys take concentrated water, seasonal movement, debris abrasion, and handling during installation. A heavier valley metal is less flimsy, lays flatter, and is generally more durable than thin, light-gauge metal.

For transitional details such as valleys, step flashing, headwall flashing, and backpans, West Country Roofing commonly leans toward a heavier 26-gauge metal package rather than treating every piece of sheet metal as an afterthought.

What to compare in a valley detail

  • Metal profile: W-valley, flat valley, or another approved detail.
  • Metal gauge: whether the estimate specifies the thickness or leaves it vague.
  • Finish: colour, coating, corrosion resistance, and how it will look with the shingles.
  • Underlayment: what membrane sits beneath the valley metal.
  • Fastening: nails should not be placed where valley water is intended to run.

What goes underneath the valley metal

The valley metal is not the only protection. A good valley assembly starts beneath the metal with deck preparation and waterproofing. Many roofs use ice and water shield in the valleys before the metal is installed, because valleys are more exposed to water concentration and freeze-thaw stress than ordinary roof field areas.

The goal is redundancy. The visible metal controls the majority of water. The membrane beneath it protects the deck if wind-driven rain, ice, debris, or an installation issue allows water to get below the surface layer.

Why straight layout matters

Open metal valleys are highly visible. A crooked cut line, uneven exposure, jagged shingle edge, or inconsistent reveal will stand out from the ground, especially on lake-view homes, hillside homes, and roof planes visible from neighbouring properties.

Good valley work is both technical and visual. The shingle courses have to land properly, the cuts need to be clean, and the exposed metal should look intentional rather than accidental.

Completed shingle roof showing visible valley and roof layout
Metal valley details affect both water management and how clean the finished shingle roof looks from the ground.

Common valley problems

Valley problems are often caused by a combination of weak materials and poor detailing. A roof can have a decent shingle installed but still fail at the valley if the metal, underlayment, cuts, or fastening are wrong.

ProblemWhy it mattersBetter approach
Nails too close to centreFasteners end up in the water path.Fasten outside the main drainage area and follow the valley detail.
Short or narrow metalLess protection where water is most concentrated.Use properly sized valley metal with correct overlap.
No membrane belowThe assembly has little backup protection.Use appropriate valley underlayment before the metal goes on.
Poor shingle cutsWater can catch edges and the finished roof looks messy.Snap clean lines and maintain consistent reveal.
Planning a roof replacement?

Ask what valley detail is included.

Valley metal is a small part of the visible roof, but it handles a large share of the water. It should be clearly specified, not hidden inside vague roofing language.

Discuss Your Roof System

Practical summary

What to remember

  • Valleys carry more water than ordinary roof field areas.
  • Open metal valleys are easier to inspect and keep the main water path on metal.
  • W-valley metal adds a centre rib that helps define and stiffen the drainage channel.
  • Gauge, coating, underlayment, fastening, and shingle cuts all matter.
  • A clean valley should perform well and look straight, deliberate, and finished.
Are open metal valleys better than closed valleys?

Not automatically in every case, but open metal valleys are often preferred because they keep the main water path visible, durable, and easier to inspect. The correct choice still depends on the roof design, shingle product, and installation instructions.

Should valley metal be visible?

On an open valley, yes. The exposed metal is intentional. When the shingle cuts are straight and the colour is chosen well, it can look clean and professional.

Does valley metal stop all leaks by itself?

No. Valley metal works with underlayment, overlap, slope, fastening, and shingle layout. The whole assembly matters.

Written by

West Country Roofing

Local, family-run roofing for Kelowna and communities throughout the Okanagan, with generations of roofing experience dating back to 1932.