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Roof valley types

2026-09-04 · 6 min read

Bids & the job
Two-colour print of a roof valley between two planes

Two planes meeting, the valley running to the eave.

The three details

A valley is where two roof planes meet and every drop of water on both of them ends up. It is the highest-volume place on any roof, and there are three accepted ways to build it.

TypeHow it is builtBest on
OpenMetal down the centre; shingles cut back on both sides to leave a channelHigh-volume valleys, snow, debris, heavy rain
Closed-cutOne plane run through; the other trimmed to a line just off centreMost residential roofs; the default today
WovenCourses from both planes interlaced across the centre3-tab shingles at equal pitch; rare on laminates

Choosing between them

Open valleys move the most water and shed debris the best, and they are the only sensible choice where snow slides or where a large plane drains into a small one. They also read as a deliberate detail rather than a joint, which is why they are common on architect-drawn roofs.

Closed-cut is faster, cheaper and invisible, and it is entirely adequate on ordinary residential valleys of similar pitch. Woven is largely historical: most laminate shingles are too thick to weave cleanly, and manufacturers increasingly exclude it.

Two-colour print of a closed-cut valley
A closed-cut valley: one plane through, one trimmed.

How each one fails

Open: valley metal too narrow, or fastened through its middle so the fasteners sit in the water path. Metal should be held at its edges only.

Closed-cut: the cut line drifting into the centre so the trimmed shingles sit in the flow, or nails driven within six inches of the centre line — a nail in the valley is a nail in a stream.

Woven: a laminate forced to weave, which leaves the shingle unsupported over the centre where it eventually cracks.

Membrane first, always

Every valley gets a full-width self-adhering membrane down the centre before anything else, regardless of type. It is the layer that holds when ice backs water up the valley — see the underlayment guide.

Two-colour print of a woven roof valley
A woven valley, courses interlacing.

What a valley does to the takeoff

Every course meeting a valley loses its tail to a cut, and those offcuts are waste. One or two valleys move a roof from the 10% waste band to 15%; a genuinely cut-up roof with several valleys and dormers earns 18% or more. Set it on the square calculator before you order, and add the valley metal by the linear foot on the estimate sheet.

Related

Sources

  1. International Building Code 2021 §1507.2, asphalt shingles — read 2026-09-04
  2. International Building Code 2021 §1507.1.2, ice barriers — read 2026-09-04