Roofing component
What is a roof valley?
The trough where two slopes meet and pour their water into one channel — the busiest square feet on the roof, and the ones built most carefully.
Updated September 12, 2026 · Every figure links to its source · Sources
DefinitionComponentAlso called: valley, open valley, closed valley, woven valley
Roof valley — the internal angle formed by the intersection of two sloping roof planes, down which the water from both drains toward the eave; the NRCA glossary defines it so, and the 2021 IRC, Section R905.2.8.2 requires valleys on shingle roofs to be lined, and sets the lining materials and widths.
What it is
Wherever a roof turns a corner in plan — an L-shaped house, a cross gable, a dormer — two slopes meet at an inside angle and their water runs together down it. The valley therefore carries more water, faster, than any other part of the roof, and it is where leaves and snow collect. The IRC, Section R905.2.8.2 requires valley linings under asphalt shingles, installed to the manufacturer's instructions, and its table lists the acceptable lining materials — sheet metals of specified thickness for open valleys and, for closed valleys, a self-adhering membrane or two layers of underlayment.
Three ways of shingling it are in use. In an open valley the metal lining is left exposed down the centre, the shingles from each side cut back parallel to it; it drains fastest, clears debris best and shows the metal. In a closed-cut valley the shingles from one slope run across the valley and the other slope's shingles are cut in a straight line just off centre, over a membrane; it is the common residential detail. In a woven valley the courses from both sides are interlaced across the valley with no cut, over a membrane; it hides the joint and suits lighter shingles but bunches heavy laminated ones. The directory's how-to on shingling a valley shows each.
Why it matters
A valley concentrates everything that makes a roof leak: volume, speed, debris and, in cold climates, ice. The lining is its defence, and the failures are predictable — no membrane under a closed valley, metal that has rusted through or been nailed through its centre, shingles cut too close to the centreline so water runs under the cut edge, and, worst, a dead valley: a valley that ends against a wall or another slope instead of at an eave, so the water has to turn, and pools. Dead valleys are where a cricket or a full membrane lining earns its keep. The IBHS FORTIFIED standard's sealed-deck requirement covers valleys as part of the deck.
What it costs and who does it
On a re-roof, valleys are line items by the linear foot — the membrane, the metal if open, and the extra cutting — and a house with several is slower to shingle, which the estimate reflects; a valley repair on its own is a service call plus the length rebuilt. Roofing contractors do the work. The directory's roof repair cost guide explains how such repairs are priced, and its guide to roof repair what a repair visit should include.
Frequently asked questions
Short answers; the sections above carry the detail and the sources.
What is the difference between an open and a closed valley?
Does a roof valley need metal?
What is a dead valley?
Next step
Find a roofer who does this
A roofer's valleys are the best sample of their work you can see from the ground. The directory lists roofing contractors by state and city.
Sources
- Roofing glossary — National Roofing Contractors Association (NRCA)
- 2021 International Residential Code, Chapter 9: Roof Assemblies — International Code Council (ICC)
- FORTIFIED Roof: requirements and rated roof covers — Insurance Institute for Business & Home Safety (IBHS)