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Open valley vs. closed valley: what the difference actually changes

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The valley on your roof was built one of three ways, and that single decision decides what a leak looks like from the ground, years later.

An open valley leaves a strip of metal running down the centre where two roof slopes meet, with the shingles on each side cut back from it. A closed valley hides that metal (or skips it in favor of a wide underlayment strip) and runs shingles across the channel instead. In a woven valley, alternating courses from both slopes lie over one another.

In a cut valley, one slope's shingles run through and the other side is trimmed to the line and sealed against it. That makes three methods, not two. The difference is decided once, at installation, and a homeowner does not pick it later.

What decides which one a roof gets

The main factor is the shingle itself. Thin, three-tab shingles can be woven without much trouble. Thicker architectural (dimensional) shingles usually cannot: they do not bend cleanly enough at the crease. And a good number of manufacturers either discourage weaving them outright or specify a closed-cut method in their installation instructions instead. That is the real reason woven valleys have become less common even though nothing about them is inherently wrong.

Beyond the shingle, it comes down to the roofer's own practice and, in some regions, local building convention. Open valleys need a wider strip of exposed underlayment and metal, which takes a little more material and a little more skill to crimp and seam correctly. Closed methods use less metal, or none at all beyond the ice-and-water membrane every valley needs underneath, regardless of which of the three finishes goes on top.

What each one lets you see from the ground

This is where the choice matters to you directly, years after the roof went on. With binoculars from the ground, an open valley shows its condition: you can watch for a dull, chalky. Or rust-streaked band running down the metal, for a seam that has opened where two lengths of metal meet. Or for a nail head that was driven through the exposed strip where none should be. It is the one valley type that gives you real, direct evidence.

A closed-cut valley gives you one useful tell: the cut edge. Look for granule loss or a lifted corner right along the line where the trimmed shingles meet the ones running through. A woven valley gives you almost nothing to look at. There is no metal in view and no single cut line, only an alternating pattern of shingle tabs. So a failing woven valley is read from the inside of the attic or from staining on the ceiling below it, not from the yard.

Durability is not as simple as "open is better"

Open valleys shed pine needles and debris better, since there is no shingle edge to catch them. And the metal itself, when it is aluminum, galvanized steel, or copper and properly formed with a center rib, resists wear from years of concentrated water flow.

But an open valley is only as good as its installation: a metal strip cut too narrow. Or a missing center crimp that lets water cross from one side to the other in a downpour, causes exactly the kind of leak the design is supposed to prevent.

Closed-cut and woven valleys trade that visible metal for a lower profile and, in the case of woven, a continuous shingle surface with no seam at all. Done correctly with the right shingle, both last as long as the roof around them. The trade is not durability so much as diagnosability: you find out about a closed or woven valley problem later. And from a different room, than you would with an open one.

Working out what you have

Stand where you can see the valley clearly and look for a visible metal strip running down its centre. If you see one, it is open. If you see continuous shingle with no metal and no single cut line, it is most likely woven.

If you see a straight cut edge on one side, sealed against the shingles running through on the other, it is closed-cut. On an older roof it is not always obvious from a distance. And that is fine: it is information for a phone call, not a repair you make yourself.

None of this changes how the valley itself is fixed once something is wrong with it. That work is steep and fast-draining, and it means stripping back shingles that are sealed to the deck. It is a job for someone with the training and equipment to do it without damaging the roof around it.

What changes is how early you can notice a problem. And being able to describe the valley type to a roofer on the phone, along with what you can see, gets you a faster and more accurate answer.

Frequently asked questions

What is the difference between an open and a closed valley?

An open valley leaves a strip of metal exposed down the centre of the channel, with shingles cut back on both sides. A closed valley covers that channel with shingles instead, either woven from both slopes or cut so one side runs through and the other is trimmed to the line.

What is a woven valley, and how is it different from a closed-cut valley?

Both hide the metal underneath, but a woven valley alternates full courses of shingles from each slope over one another with no cut edge at all. A closed-cut valley runs one slope's shingles through the channel and trims the other slope's shingles to that line, leaving a single visible seam.

Can architectural shingles be woven into a valley?

Often not cleanly. Thicker architectural (dimensional) shingles tend not to bend well enough at the crease for weaving, and many manufacturers' installation instructions either discourage it or specify a closed-cut method instead for that reason.

How can I tell which type of valley my roof has from the ground?

Look at the valley with binoculars. A visible metal strip down the centre means open. Continuous shingle with a single straight cut line on one side means closed-cut. Continuous shingle with an alternating pattern and no cut line means woven.

Does the valley type affect how long it lasts?

Not on its own. All three last as long as the rest of the roof when installed correctly with the right shingle and the right underlayment beneath them. What changes between them is how much you can see about their condition from the ground before a leak shows up.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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