Field guide

Roofer Roof Valley Pages That Explain Open and Closed Valleys Honestly

October 21, 2026

Direct answer: A valley is where two roof planes meet, and it concentrates the runoff of both into one channel, which is why valley detailing decides how a roof ages. A valley page should explain the two common builds, closed valleys with shingles woven or cut through the joint, and open valleys with an exposed metal flashing, usually W style, that sheds water visibly, plus the leak truth: most valley leaks come from fasteners, debris dams, and cut shingles placed too close to the centerline, not from the concept.

Stand on the ground after a hard rain and watch a roof work. The field of shingles sheds a sheet. The valley carries a river. Owners rarely think about that channel until a stain appears on a ceiling below a valley line, and then it is the only part of the roof they think about.

A roofer's valley page can do better than a photo gallery. The open versus closed argument is a real one in the trade, and owners deserve the honest version before they sign for a reroof.

Open valleys: metal does the work in plain sight

An open valley lays a metal flashing, commonly 24 inch wide W valley metal with a raised center rib, over the underlayment, and the shingles stop short on both sides so the metal channel stays exposed. Water runs on metal, the rib keeps fast moving runoff from crossing under the opposite shingle edge, and the whole assembly can be inspected from a ladder.

The costs are appearance and the metal line itself. Some owners dislike the visible stripe. In exchange they get the longest lived valley detail, especially under heavy tree cover, where a shingle surface valley grinds debris into itself every season.

Closed valleys: cleaner look, stricter rules

A closed cut valley runs shingles from one plane across the joint and trims them in a straight line offset from the center, so no metal shows. It looks tidy and it works when it is built exactly right: no fasteners within about 6 inches of the centerline, the cut kept off the center, and the underlying plane's shingles extended far enough up the opposite slope.

That precision is the catch, and a candid page says so. Closed valleys concentrate the most common workmanship errors on the roof, and they are harder to inspect and repair without disturbing a wide area of shingles. Woven valleys, the older alternating pattern, have mostly fallen away with modern architectural shingles, and a page still offering them as the default is telling you something about the page.

Why valleys leak, in order of likelihood

Debris first. Leaves and granules dam the channel, water backs up and sideways under shingle edges, and a valley that was fine in June leaks in November. Second, nails too close to the centerline, hidden until water finds the holes. Third, shingles cut on the centerline instead of offset, giving water a straight path into the joint.

The repair conversation follows the same order. Clean and inspect before anyone quotes a tear out. A valley leak with sound metal and a debris dam is a maintenance bill. A valley leak with fasteners in the channel is a rebuild of that section, and the page that separates those outcomes in advance is the page that gets the call.

Frequently asked questions

Which is better, an open or closed valley?

For durability and inspectability, an open metal valley generally wins, especially on steep roofs and under trees. A closed valley looks cleaner and performs well when installed with strict fastener and cut placement. The honest answer is that installation quality decides more than the type, and open valleys forgive more.

How long should a valley last?

A properly built open metal valley should last the life of the shingle roof around it, often 20 years or more, with debris clearing as the main upkeep. Closed valleys also last when built correctly, but their failure points are hidden, so problems tend to announce themselves as interior leaks rather than visible wear.

Can a leaking valley be repaired without a new roof?

Often, yes. Debris removal, resealing exposed fasteners, and in larger cases lifting and rebuilding the valley section are all standard repairs when the surrounding shingles are still serviceable. If the shingles around the valley are at end of life, money spent rebuilding a valley inside a failing roof is usually better put toward the reroof.

Why does my valley leak only in heavy rain or fall?

Volume and debris. A valley carries the combined runoff of two roof planes, so heavy rain tests every marginal detail in it, and autumn debris dams slow the channel and push water sideways under edges that lighter rain never reaches. Seasonal leaking is a classic valley signature.