Open vs Closed Roof Valleys in Michigan Snow Country

Most of a roof sheds water in a straight line, downhill, across a field of shingles built for exactly that. A valley is the exception. It is the inward angle where two roof planes meet, and it collects the runoff of both slopes into a single channel that is narrower than either plane on its own. On a wide gable roof with a simple hip, a valley might carry only modest flow. On a cut-up Macomb County roof with dormers, an attached garage, and a couple of roof-plane changes, a valley can be handling several times the water per square foot that the open field ever sees, and it does that job every rainstorm and every snowmelt for the life of the roof. How that channel is detailed, woven, closed-cut, or open metal, is one of the more consequential decisions on a reroof, and it is one most homeowners never hear discussed unless they ask.

01 / THE SHORT ANSWERWhich valley style wins in snow country

All three valley styles can be built correctly and can fail if they are not. But in a climate that stacks snow in valleys and puts that snow through repeated freeze-thaw cycles, an open metal valley generally has the strongest case. It exposes a continuous metal channel that sheds water and meltwater fastest, resists the ice-dam backup that forms when snow sits and refreezes in a tight channel, and it is the easiest style to inspect and repair without disturbing the shingle field around it. Woven and closed-cut valleys are shingle-over methods that can perform well on a straightforward roof with a good installer, but they ask more of the shingles themselves in exactly the spot doing the hardest work on the roof.

The rest of this guide walks through why valleys take more punishment than the rest of the roof, how each style handles that punishment, and the one detail that matters regardless of which style ends up on your house.

02 / THE LOADWhy a valley works harder than the rest of the roof

Two mechanisms make a valley the hardest-working few feet of any roof. The first is simple geometry: runoff from two full roof planes converges into a channel that is a fraction of either plane's width, so the water depth and flow speed in a valley during a hard rain are meaningfully higher than anywhere else on the roof. The second is winter-specific. Snow tends to accumulate deeper in a valley than on the open field, because wind and gravity both push loose snow toward the low point between two slopes. That deeper snowpack takes longer to melt and refreezes more readily at night, which means a valley can be running a private ice-dam cycle even on a roof where the eaves are clear.

Put those two mechanisms together and a valley is doing double duty: carrying the most concentrated water flow on the roof during rain, and holding the most persistent snow and ice load during winter. Whatever detail sits in that channel needs to handle both without a seam that lets water find the deck underneath, which is exactly what separates a valley that lasts decades from one that reopens the same leak every spring.

03 / WOVENWoven valleys: shingles interlaced across the seam

A woven valley is built by running shingle courses from both adjoining roof planes across the valley centerline and overlapping them into each other, course by course, so no metal channel is ever visible; the shingles themselves form a continuous, interlaced mat over the low point. It was once the default valley style on many asphalt roofs, largely because it uses only shingles, no separate metal, and can look tidy when done well.

The tradeoff is that the shingle material itself becomes the only barrier standing between the valley's concentrated water flow and the deck below, and the interlaced seam is thicker and less flexible than a single shingle layer, which can make it more prone to cracking as it ages and flexes through freeze-thaw cycles. Some shingle manufacturers also restrict or discourage weaving with certain laminated or high-profile products, since the extra thickness at the overlap can interfere with proper sealing. Woven valleys have become less common on newer Macomb County reroofs as a result, though a well-built one on a straightforward roof can still perform adequately for years.

04 / CLOSED-CUTClosed-cut valleys: one plane laps over, the other is trimmed

A closed-cut valley runs shingles from one roof plane fully across the valley first, then shingles from the second plane are trimmed along a straight line a few inches back from the centerline, so only one plane's shingles actually cross the seam. The cut edge is set back far enough that the exposed edge is not directly in the heaviest flow path, and the result reads as a clean, mostly hidden line rather than the visible metal channel of an open valley.

Closed-cut has become the more common shingle-over method on newer roofs, in part because it is faster to install than weaving and does not require the manufacturer accommodations that weaving sometimes does. It still relies on shingles and the underlying membrane rather than an exposed metal channel to do the water-shedding work, and the cut edge, while set back from the centerline, is still a seam that a careful installer needs to seal and maintain cleanly. Ice or debris that collects at that cut line can, over time, work under the trimmed edge in a way that a fully open channel would simply shed.

05 / OPEN METALOpen metal valleys: a continuous channel, nothing to weave or cut

An open metal valley leaves a strip of metal, typically several inches wide, exposed down the centerline of the valley, with shingles from both roof planes trimmed back from the metal rather than crossing over it. Water and meltwater run down a single, continuous, low-friction surface with no shingle seam anywhere in the flow path, which is the main reason it tends to perform best where snow sits and refreezes: there is no interlaced or trimmed shingle edge for ice to work against.

Why the case is strongest in snow country

Metal sheds meltwater faster than a shingle surface, which shortens how long standing water and slush sit in the channel during a thaw. It also gives a valley one continuous surface rather than a seam built from smaller overlapping pieces, so there is less opportunity for ice to lever a gap open the way it can at a woven or closed-cut edge. And because the channel is visible rather than buried under shingles, an open metal valley is the easiest of the three styles to inspect from a ladder or during a routine roof check, and the easiest to repair or reflash later without disturbing shingles on either side.

The visible metal is sometimes seen as a cosmetic tradeoff, since it reads as a distinct line down the roof rather than blending into the shingle field the way woven and closed-cut valleys do. On most Macomb County homes that line is a minor detail next to the performance and serviceability difference, and it is one worth discussing with whoever is quoting your reroof rather than assuming the cheaper, faster shingle-over method is the equivalent choice.

06 / THE FOUNDATIONWhat belongs under any valley, regardless of style

Whichever style ends up on your roof, one requirement does not change: a full-length ice and water shield membrane under the valley, running the entire length from ridge to eave and extending well up both adjoining roof planes. That self-adhering membrane is what actually seals around fasteners and handles water that gets past the surface detail above it, whether that surface is woven shingles, a closed-cut edge, or open metal. Our companion guide on ice and water shield placement covers this membrane in full, including the other zones of a roof where it belongs.

A valley that gets a spliced or partial run of membrane underneath it is vulnerable no matter how well the visible shingle or metal work is finished on top, because the membrane is the actual backstop when the surface detail is overwhelmed by a hard storm or a stubborn ice dam. This is also where flashing quality and valley detailing intersect with the rest of a reroof; our guide to new roof flashing details covers the broader set of metal work a full replacement should include, including the corner-cutting we see most often on valleys specifically: reusing sections of old metal rather than running a new, full-length piece.

07 / YOUR ROOFLINEChoosing the right valley for a complex roofline

A simple gable roof with one or two straightforward valleys gives you real flexibility in valley style, since none of the three methods is being asked to do anything unusual. A complex roofline with multiple intersecting planes, dormers, or a shallow-pitch section feeding into a steeper one is a different conversation. Low-slope transitions in particular tend to create what roofers sometimes call dead valleys, sections with very little pitch where water moves slowly and has more time to find a weak seam. Our guide on dead valleys and complex rooflines covers that scenario in more depth, including why an open metal approach or a reinforced membrane detail often makes more sense there than a standard shingle-over valley.

A valley only has to fail once, in the one spot that carries the most water on the whole roof, to turn a routine winter into an interior repair bill.

Serviceability is worth weighing too, especially if your home has a history of ice damming or a roofline with several valleys feeding a single drainage path. An open metal valley that develops a problem years down the road can often be reflashed or repaired without touching the shingles on either side. A woven or closed-cut valley that fails usually means opening up shingle courses on both adjoining planes to get at the seam underneath, which is a larger repair for the same underlying problem. None of this means a well-built closed-cut or woven valley is a bad choice on the right roof; it means the decision is worth making on purpose, with your specific roofline and history in mind, rather than accepting whatever a bidder defaults to without asking why.

The honest way to make that call is a free inspection: walking your actual roof, counting your actual valleys, and looking at how much snow and ice they have historically held. If your roofline is simple, we will tell you a shingle-over valley is a perfectly reasonable choice. If it is complex, or if you have had ice-related leaks in a valley before, we will explain exactly why open metal is worth the small visual tradeoff. Either way, you get a written recommendation with reasons attached, not a default. You can start with the instant estimator, run your numbers through the cost calculator, or see the full breakdown in our roof replacement cost guide, and the full published ranges are always on our honest pricing page.