Valley Leak Woven vs Cut vs Open Metal Decision Tree

Why this matters

Valleys carry the concentrated runoff of two roof planes, so they leak more than almost any other detail when built or maintained wrong. There are three common constructions, woven, closed-cut, and open metal, and each fails in a different way and demands a different fix. A tech who treats every valley leak the same will caulk a woven valley that needs rebuilding, or replace open metal that just needs debris cleared. Diagnosing which valley type you have and which failure mode it is showing is the only way to repair it once instead of three times. The volume and velocity of water in a valley punish any shortcut.

Symptom presentation

The customer reports leaks during heavy rain that track to a valley, often staining a ceiling near the junction of two roof sections. On the roof you find one of three valley types: shingles woven across the valley from both slopes, shingles from one slope cut along a chalk line over the other (closed-cut), or exposed metal flashing running down the center. The leak may worsen with debris buildup, wind-driven rain, or after a roof of a different pitch was added. Granule loss in the valley center and exposed nail heads near the valley are common findings.

Quick checks

Identify the valley type first, because the repair branches from it. In the attic, confirm the wet track originates at the valley and runs down from it. On the roof, check the valley for debris damming water, fasteners placed too close to the valley center line, and the condition of any underlayment or metal visible. For open metal, check for corrosion, a flattened or reverse-W center rib, and end laps running uphill. For closed-cut, check whether the cut line was sealed and whether the underlying shingles run far enough across. For woven, check for lifted or cracked shingles where they bend through the valley.

Isolation tree

Branch by valley type, then by failure mode.

• Open metal valley. Suspect debris damming runoff over the edge, fasteners driven through the metal within the clear zone, corrosion holes, or end laps lapped uphill so water runs under. Clear the valley and inspect the metal center and laps. Open metal is the most forgiving type when clean and the most leak-prone when penetrated by nails.
• Closed-cut valley. Suspect the cut line not sealed, the underlying course not extended at least the required distance past the centerline, or nails set too near the cut. Water from the cut slope rides over the trimmed edge and under the underlying course. Lift the cut edge and check seal and overlap.
• Woven valley. Suspect cracked or fatigued shingles where they bend through the valley, or fasteners in the valley center. Woven valleys stress the shingle at the bend and crack with age and cold. Inspect for cracks and exposed nails.
• Any type with a high-volume or pitch-mismatch condition. A low-slope plane feeding a steep valley, or two large planes converging, overwhelms a woven or closed-cut valley. Confirm the contributing area and pitches.
• Track originates above the valley at a penetration or wall. Then the valley is downstream, not the source. Stop this tree and inspect the upslope detail.

Confirming diagnosis

Run water down the valley in stages. Start low and wet a short length of the valley, then move uphill, while a helper watches the attic track with a moisture meter. The breach is the lowest point at which the leak reproduces. For open metal, watch whether water sheds off the center rib or finds a fastener or lap; lifting nearby shingles often reveals a nail penetrating the metal. For closed-cut, lift the cut edge during the test to see whether water rides under the underlying course at the trim line. For woven, flex the shingle at the bend to expose hairline cracks that open under water pressure. Heavy-flow valleys are best confirmed with a higher-volume test that mimics storm runoff, since a trickle will not overtop a marginal detail.

Remediation

Match the fix to the type. For open metal, clear all debris, replace corroded or punctured metal with a center-ribbed (W or V) valley flashing, lap the metal sections shingle-fashion with the uphill piece over the downhill piece, and keep all fasteners outside the clear zone with no nails through the metal. For closed-cut, where the leak is from a short or unsealed cut, the durable fix is to open the valley back up and rebuild it as open metal or re-lay the cut with the underlying course extended well past the centerline and the cut edge set in mastic, with nails kept clear of the cut. For woven, replace cracked shingles, and if the volume is high or the shingles are brittle, convert to open metal, which handles concentrated flow better than woven on steep or high-flow valleys. Always install ice-and-water membrane in the valley before any covering per IRC requirements in applicable climates. After any repair, re-run the staged valley water test to confirm.

References

• IRC R905.2.8.2 (valley flashing and underlayment requirements for asphalt shingles)
• IRC R905.1.2 / R905.1.1 (ice barrier membrane in valleys where required)
• NRCA Roofing Manual (open, closed-cut, and woven valley construction and repair)
• ASTM D1970 (self-adhering polymer-modified ice-and-water underlayment)