The valley carries more water than any other part of a roof, which is exactly why it leaks first. How it is built matters more than almost any other detail.
Quick answer: A roof valley is where two slopes meet and drain, so it moves the most water and fails first. There are three ways to build one: an open valley runs water on exposed metal, a closed-cut valley runs it on shingles cut off the centerline, and a woven valley interlaces the shingles across. In West Michigan the open metal valley lasts longest because it sheds snow and ice and does not abrade. All three need a full ice and water membrane underneath, which the code requires.
Every roof has a weakest point, and on most homes it is a line you can see from the street. A valley is the internal angle where two roof planes meet, and it works like a gutter set into the roof itself. All the water that falls on both slopes funnels into that channel and races down it. On a big historic roof with dormers and gables, a single valley can carry the runoff of hundreds of square feet in a hard rain. That concentration is why valleys are the first place a roof leaks, and why the way a valley is built tells you more about a roof's real quality than the color of the shingles.
Grand Rapids makes the stakes higher. The National Weather Service Grand Rapids office tracks 40 to 60 freeze-thaw days in a typical winter, and a valley packed with snow and ice is a slow-motion test of the assembly beneath it. Meltwater backs up, refreezes, and probes every seam. A valley built for looks and not for water will find that out by February. A valley built right sheds it and never says a word.
There are only three, and they are not equal. The difference comes down to one question: does the water run on metal, or on shingles?
An open valley leaves a channel of exposed metal flashing running down the center of the valley, with the shingles trimmed back in a clean line on each side. Water runs on the metal, not the shingles. This is the traditional detail on slate, copper, and premium roofs, and on a West Michigan home it is the one we reach for first. The metal is usually a W-profile, meaning it has a raised rib down the center that keeps water from washing across from one slope to the other during a downpour.
A closed-cut valley carries the shingles from one slope straight through the valley, then laps the shingles from the second slope over the top and cuts them in a straight line just off the centerline. The valley surface is all shingle, with the metal or membrane hidden underneath. It is clean, it is fast, and it is the most common asphalt detail built today. It works, but the water runs on shingle granules, and that surface wears faster than metal.
A woven valley interlaces the shingles from both slopes, alternating one over the other all the way down so the valley is a continuous woven surface with no cut line. It was the standard in the three-tab era. On today's roofs it is the weakest of the three, for reasons worth spelling out.
| Valley type | Water runs on | Best for | Relative lifespan |
|---|---|---|---|
| Open metal (W-profile) | Exposed metal | Slate, copper, historic, steep or high-flow roofs | Longest, often outlasts the shingles |
| Closed-cut | Shingles | Standard asphalt roofs, clean modern look | Good, wears with the field shingles |
| Woven | Shingles | Older three-tab work only | Shortest, poor with laminate shingles |
Ask any roofer who has pulled apart a forty-year-old roof which valley was still doing its job, and the answer is the metal one. An open metal valley is the strongest and longest-lasting of the three, and the reasons are all about how it handles water and winter. The smooth, hard surface sheds snow and ice instead of gripping it, so ice does not build the way it does on a granular shingle valley. Water flows freely down the channel rather than soaking across shingle laps. And the metal simply does not abrade under constant flow the way a shingle surface does, so it ages with the rest of the roof rather than wearing out in the middle first. Manufacturers like IKO make the same point: for heavy water and snow, the open valley with proper flashing is the durable choice.
The material is chosen to match the roof. Prefinished steel and aluminum valleys are standard and economical on asphalt roofs. On slate and historic homes, copper is the traditional and correct choice, weathering to a patina that belongs with an aged roof and lasting for generations. This is the same match-the-metal logic that governs a copper roof or a slate restoration, where the valley is not an afterthought but part of the roof's character.
The woven valley did not get worse. The shingles did. When roofs were covered in thin, flexible three-tab shingles, weaving them through a valley was reasonable, and plenty of those valleys held up. Today's architectural, or laminate, shingles are thick and stiff by design. Forcing a rigid laminate shingle to bend through the sharp angle of a woven valley creates stress points where the shingle wants to lift and crack, and every one of those is a path for water. That is why most shingle manufacturers now steer architectural shingles away from woven valleys entirely and toward closed-cut or open metal.
So the practical rule for a modern West Michigan roof is short. If it wears laminate shingles, the valley should be open metal or closed-cut, never woven. A crew still weaving architectural shingles is building a valley that will crack where it bends, and in a freeze-thaw climate that is the fast lane to a leak.
The visible valley is only the top layer. The waterproofing is underneath, and the code is specific about it. Before any metal or shingle goes down, the valley gets a continuous run of self-adhering ice and water membrane. Under the International Residential Code that Michigan has adopted, that membrane is required in valleys, and section R905.1.2 mandates a self-adhering underlayment on low slopes where the risk is highest. The National Roofing Contractors Association recommends the membrane run at least 36 inches wide, 18 inches on each side of the valley centerline, in every climate zone, and most shingle warranties will not stand without it.
In a lake-effect climate that requirement is not a formality. When an ice dam or a spring thaw backs water up the valley, that membrane is the last line that keeps it out of the deck and the ceiling below. We treat it as non-negotiable, and it is the same membrane discipline we cover in our guide to ice and water shield requirements under Michigan code. A beautiful open copper valley over a bare deck is a leak waiting to happen. The order of operations, membrane first, metal second, shingles cut last, is the whole craft.
A valley can often be rebuilt on its own when it leaks but the surrounding shingles have years left. The roofer opens the valley, strips the old metal and underlayment, lays fresh membrane, sets new flashing, and re-cuts the shingles into it. It is exacting work, because this is the most water-loaded line on the roof and there is no margin for a sloppy cut. When the field shingles are already near the end of their life, though, the better value is to rebuild the valleys as part of a full replacement, so the new valley and the new roof age together on the same clock.
That judgment, repair the detail or replace the roof, is the heart of what we do. Valleys are part of every roof we build in our residential roofing work, and getting them right is one more place where thirty years of West Michigan winters teaches you not to cut corners.
The valley is where a roof is won or lost. On a West Michigan home the open metal valley is the standard worth paying for: it sheds snow and ice, it moves heavy water on metal instead of shingle, and it lasts. Closed-cut is a fair modern option on an asphalt roof, woven belongs to the three-tab past and has no place under stiff architectural shingles, and all three are only as good as the ice and water membrane the code requires beneath them. Build the valley right, in the correct order, and the roof will keep the weather out at its weakest point for as long as the shingles last.
Whether your valleys need a targeted rebuild or a full historic roof, our services cover it, and we have been keeping water out of West Michigan roofs at their hardest-working detail since 1994.
An open metal valley. It sheds snow, ice, and heavy water flow better than shingle-based valleys because the surface is smooth and hard, it wears far more slowly, and it ages with the rest of the roof. In a climate with 40 to 60 freeze-thaw days a winter, the open metal valley over a full ice and water membrane is the longest-lasting choice, and it is standard on slate, copper, and premium homes.
An open valley leaves a channel of exposed metal down the center, so water runs on the metal. A closed-cut valley runs shingles from one slope across and cuts the other slope's shingles just off the centerline, so water runs on shingles. A woven valley interlaces the shingles from both slopes across the valley. Open runs on metal, closed-cut and woven run on shingles.
Yes. Self-adhering ice and water membrane in the valley is required by code for low slopes under Michigan's adopted IRC, and most shingle manufacturers mandate it in valleys to keep the warranty valid. The National Roofing Contractors Association recommends the membrane run at least 36 inches wide, 18 inches each side of the centerline, in every climate. In West Michigan it is not optional.
They are a poor match. Thick, stiff architectural shingles do not bend cleanly through a woven valley, so forcing them creates stress points that crack and let water in. Most manufacturers steer architectural shingles toward closed-cut or open metal valleys instead. Woven valleys were a three-tab-era method, and on modern laminate shingles they are the weakest of the three options.
A properly built open metal valley typically outlasts the shingles around it, and in copper it can last for generations. The metal does not abrade the way shingle surfaces do under constant water flow, so it holds up through decades of West Michigan freeze-thaw. Prefinished steel and aluminum valleys are common on asphalt roofs, while copper valleys are the traditional match on slate and historic homes.
Sometimes, and it is a common repair when a valley leaks but the field shingles have life left. The roofer opens the valley, replaces the underlayment and metal, and re-cuts the shingles into it. It is precise work because the valley carries the most water on the roof. When the surrounding shingles are near end of life, rebuilding the valley during a full replacement is the better value.
Roof Repair of Grand Rapids has been installing, repairing, and preserving roof systems on West Michigan homes since 1994. Our crews build valleys on everything from downtown asphalt roofs to Heritage Hill slate and copper, matching the valley type and metal to the roof and setting the ice and water membrane the way the code and the climate demand. We assess the water load and the shingle before we choose the detail, because on a Grand Rapids roof the valley is where the winter goes to work. Authoritative reference for this guide: IKO roofing on open versus closed valleys.