Which is better, open or closed roof valleys?

Open metal valleys shed water and debris better and last longer, especially in heavy rain, snow, and leaf country. Closed-cut valleys cost less and look seamless. Performance arguments favor open; budgets and aesthetics keep closed common.

Why do roof leaks so often start at valleys?

Valleys carry the concentrated flow of two roof planes, plus every leaf and granule those planes shed, so any defect there sees more water more often than anywhere else on the roof.

What is a woven valley?

Shingles from both planes laced across the valley with no cut line, an older style limited to flexible three-tab shingles. On modern thick laminated shingles it bridges poorly, which is why it has largely retired.

Do valleys need ice and water shield?

In cold climates, yes as standard practice and often by code: self-adhering membrane under the valley, whatever the style above it, backs up the roof's busiest drainage against ice and ponded flow.

Roof Valleys: Open vs. Closed | Home Reference Guide

Page last reviewed: August 2026 · Reviewed by Harold R. Bennett, retired home inspector

A valley is where two roof planes meet and drain together, which makes it the roof’s river: double the catchment, all the debris, and, in winter, the ice. The open vs closed roof valley question is the one construction choice most visible from the curb and most consequential in a storm, and the answer divides on performance versus cost. This comparison covers both styles, the retired third, and the failure signatures each one shows.

Why valleys concentrate everything

Each plane sheds its water sideways into the valley line, so the valley carries the combined flow at the combined speed, along with every leaf, twig, and granule those planes surrender. Concentration is the whole story of valley failure: a defect that would drip occasionally in the field leaks weekly in a valley, debris dams form here first and push water sideways under the courses, and ice takes up winter residence exactly where flow ponds, which is why cold-climate practice puts self-adhering membrane under every valley as the non-negotiable base layer, kin to the eave treatment in the ice dam reference, and why valley discharge earns oversized gutter outlets at the bottom.

Open valleys: the exposed channel

An open valley lines the junction with exposed metal, W-profile steel, aluminum, or copper, with shingles from each plane stopped short of the centerline, leaving a visible metal channel a few inches wide. The performance case is straightforward: smooth metal sheds water and debris faster than granulated shingle surfaces, the W rib resists cross-wash where one plane outruns the other, snow and ice release sooner, and the channel inspects at a glance from the ground. Longevity follows, the metal typically outliving the surrounding shingles, and heavy-rain, heavy-leaf, and snow-country practice favors open valleys accordingly. The costs: material and labor above closed, an aesthetic line some buyers dislike, and the metal’s own rules, correct gauge and profile, cleats rather than face nails, and galvanic manners where copper meets other metals. Failure signatures: rust lines and pinholes in aging steel, face-nailed metal telegraphing leaks at each penetration, and shingle edges crowding the channel until debris bridges it.

Closed-cut valleys: the seamless look

The closed-cut (half-lace) valley runs one plane’s shingles across the valley line and trims the other plane’s to a clean cut just off center, over membrane and often a metal liner below: from the curb, an unbroken shingle surface. The case for it is cost and appearance, and competently built over proper membrane it serves ordinary climates respectably. Its structural honesty problem is workload: the cut plane’s shingle edges sit in the river, granule surfaces slow the flow, debris lodges along the cut line, and heavy cross-flow from a steeper or larger plane can drive water under the cut edge, which is why the trimmed corner of each shingle gets clipped and sealed in careful work, and why closed valleys age first on exactly the roofs, big planes, pines overhead, hard winters, where open metal earns its keep. Failure signatures: a debris stripe along the cut, granule wear tracking the flow line, lifted cut edges, and the wandering interior leak whose uphill hunt ends at the valley more often than anywhere else.

The woven valley, retired

The third style laces shingles from both planes across the line with no cut at all, an approach native to flexible three-tab shingles and largely retired by modern laminated products, whose thickness bridges the valley hollow, leaving voids that crack underfoot and pond beneath. Its appearance on an older roof is a dating clue and, on a thick-shingle roof, a workmanship flag.

Choosing, and living with either

New-roof guidance: open metal wherever rain intensity, snowfall, leaf load, or plane asymmetry is serious, closed-cut where climate is gentle and the seamless look matters, membrane underneath always, and the flashing-family discipline of laps-not-caulk governing every edge. Ownership is the same for both: keep the channel clear on the seasonal gutter rounds, read the debris stripe and wear line as the early warnings they are, and treat any valley leak as a rebuild-the-detail repair rather than a sealant errand, valleys being the one place a tube of caulk is most tempted and least durable.

The bottom line

Valleys carry the roof’s concentrated water and debris, open metal channels handle both better and longer, closed cuts trade some of that margin for cost and looks, and membrane belongs under either. Whichever style is overhead, the maintenance is one habit: keep the river clear, and read its banks each season.

Roof Valleys: Open vs. Closed