Have you ever looked at a roof estimate and seen the word "valley" without a single detail about how that valley will be built? If your home has any dormers, gables, or intersecting roof planes, you have valleys — and the way a crew chooses to construct them is one of the highest-consequence decisions in the entire replacement.
A valley is the internal angle where two sloped roof planes meet. Everything that lands on both of those planes converges there and runs down a single narrow channel, which means a valley can carry the drainage load of hundreds of square feet of roof through a strip maybe 12 to 24 inches wide.
That concentration is why valleys, along with penetrations like chimneys and skylights, account for a disproportionate share of the leaks roofers are called out to fix. Keep in mind that a valley failure rarely announces itself on the roof — it shows up as a stain on a bedroom ceiling months after the water started moving.
Why Valleys Carry So Much More Water Than the Rest of the Roof
Think of a valley as the roof's gutter before the gutter. Two planes, each shedding rain at the same time, dump their combined volume into one linear channel that has to move all of it to the eave without overtopping, backing up, or working sideways under the shingles.
The math is straightforward and unforgiving. A 1-inch-per-hour rainfall over 1,000 square feet of tributary roof area produces roughly 620 gallons per hour, and if two planes of that size intersect, the valley between them is handling well over a thousand gallons in an hour of moderate rain.
Velocity compounds the problem. Water moving down a steep valley picks up speed, and fast-moving water at the intersection of two planes has energy to push laterally — up under a shingle edge, into a nail hole, past a lap in the underlayment.
That lateral push is the mechanism behind most valley leaks. It is also why the details that matter most in a valley are the ones you cannot see once the roof is finished: the underlayment, the flashing, and the nailing pattern along the valley edge.
What Is an Open Metal Valley?
An open metal valley leaves the channel exposed. A preformed metal flashing — commonly 24-gauge or 26-gauge galvanized steel, aluminum, or copper — runs the full length of the valley, and the shingles from each plane are cut back to leave a visible metal strip down the middle.
The metal typically ranges from 16 to 24 inches wide, with a raised center rib (a "W" profile or a standing center crimp) that stops water from crossing from one plane to the other during heavy flow. That center rib is not decoration — on a roof where one plane is substantially larger than the other, it is what keeps the high-volume side from flooding the low-volume side.
Shingles are trimmed in a straight line on each side, usually leaving a 3-inch exposure at the ridge that widens by about 1/8 inch per foot as it runs toward the eave. That taper accommodates increasing water volume as the valley collects more area on its way down.
Critically, fasteners stay out of the channel. The metal is held with clips or is nailed only along its outer edges, well outside the wet zone, so there are no penetrations in the part of the assembly that stays wet the longest.
What Is a Closed-Cut Valley?
A closed-cut valley has no exposed metal. Shingles from one plane — conventionally the one with the lower slope or smaller tributary area — run across the valley and continue at least 12 inches up the adjacent plane, and then shingles from the second plane are laid over them and cut in a straight line about 2 inches back from the valley centerline.
The result is a continuous shingled surface with a clean cut line. It reads as a single uninterrupted field of roofing, which is the main reason many homeowners and builders prefer it aesthetically.
A closed-cut valley is not an unlined valley. Manufacturer instructions and code both call for valley lining underneath — self-adhering ice-and-water membrane is the standard, run a minimum of 36 inches wide and centered in the valley.
The variant you want to know about is the woven valley, where shingles from both planes alternate and interlace through the channel. Woven valleys are fast and were common for decades, but they are no longer permitted by most architectural shingle manufacturers because the thicker laminated shingle will not lie flat through the weave.
Open Metal vs Closed-Cut: The Head-to-Head Comparison
Both methods are code-compliant and both are approved by every major asphalt shingle manufacturer when installed to specification. The difference is not legality — it is how each assembly behaves under stress, over time, and in specific climates.
Here is how the two approaches compare on the factors that actually determine leak risk and service life:
- Water-handling capacity. Open metal wins decisively. A smooth metal channel moves water faster, sheds debris more readily, and has no granular surface to slow flow or trap sediment.
- Fastener exposure. Open metal keeps nails out of the channel entirely; closed-cut requires the overlying shingles to be nailed no closer than 6 inches from the centerline, and crews under time pressure sometimes miss that line.
- Debris shedding. Open metal sheds pine needles, leaves, and granules far better. A closed-cut valley's granulated surface holds organic debris, which holds moisture against the shingle mat.
- Ice performance. Metal valleys allow ice and snow to slide rather than bond, which matters enormously in freeze-thaw climates where ice dams form at valleys and eaves.
- Granule loss. Closed-cut valleys wear faster because the concentrated flow scours granules off the cut shingles, exposing the asphalt mat and accelerating aging in the highest-stress area of the roof.
- Appearance. Closed-cut wins for most homeowners — a monolithic shingle field with no contrasting metal stripe.
- Cost. Closed-cut is cheaper, typically by roughly $6 to $12 per linear foot of valley in most markets, driven by material cost and the extra labor to set and fasten metal.
- Repairability. Open metal is easier to inspect and easier to repair, since the channel is visible and the shingle edges can be lifted without disturbing an interlaced assembly.
All of these add up to a fairly clean rule: open metal is the more durable assembly, closed-cut is the more affordable and better-looking one, and the right answer depends on your climate, your tree cover, and your roof's geometry.
When Open Metal Is the Right Call
Some roof and site conditions push the decision decisively toward open metal. Be aware that in these situations, choosing closed-cut to save a few hundred dollars often costs more in repairs within the first decade.
Open metal valleys are the stronger choice when any of the following apply:
- Unequal roof planes. When one plane drains substantially more area than the other, the ribbed center of an open metal valley prevents the high-volume side from pushing water across and under the shingles on the low-volume side.
- Low-slope valleys. Valleys formed where two shallow planes meet produce a valley slope shallower than either plane, and slower water sits longer. Metal handles standing and slow-moving water far better than a granulated surface.
- Heavy tree cover. Overhanging pines, oaks, and maples drop debris that a closed-cut valley catches and holds. A smooth metal channel keeps moving.
- Freeze-thaw climates. In northern regions, valleys are prime ice-dam locations, and metal reduces the bonding that lets ice build in the channel.
- Long valley runs. A valley over roughly 20 feet accumulates enough volume and velocity by the eave end that the smooth channel earns its cost.
- Premium materials. If you are installing slate, tile, or cedar shake, open metal is effectively the only correct option — those materials cannot be cut and lapped like asphalt.
On a metal roof, the valley question resolves itself differently, since standing-seam and metal panel systems use a dedicated valley pan flashing with panel ends hemmed and held back from the channel.
When Closed-Cut Is Perfectly Fine
Closed-cut has a genuine place, and it would be misleading to treat it as a compromise everywhere. Millions of closed-cut valleys perform for the full service life of the shingle without a single drop of intrusion.
Closed-cut is a reasonable specification on a simple gable roof with short valleys, moderate slope, minimal tree exposure, and a climate without prolonged freeze-thaw cycling. Combined with a properly installed 36-inch ice-and-water membrane and disciplined nail placement, it is a durable assembly.
The key qualifier is installation quality. A closed-cut valley has a narrower margin for error than an open metal valley, because the things protecting it — membrane coverage, nail setback, straight cut line, dubbed corners — are all workmanship rather than geometry.
That makes the closed-cut decision partly a question about your contractor. If you are still in the vetting stage, asking how a crew builds valleys is one of the more revealing questions you can pose.
The Details That Actually Determine Whether a Valley Leaks
Neither valley type fails because of the type. They fail because of specific, identifiable installation errors, and knowing them lets you read a bid and inspect a finished job with real understanding.
The underlayment beneath the valley is the first line of defense. Code in most jurisdictions requires a minimum 36-inch-wide self-adhering ice-and-water membrane centered in the valley, and in northern climates many jurisdictions require it to extend from the eave edge to at least 24 inches inside the exterior wall line.
Nail setback is the second. Manufacturer instructions call for fasteners no closer than 6 inches from the valley centerline on closed-cut installations, and on open metal the flashing should be fastened only at its outer edges or held with clips.
Corner dubbing is the detail almost nobody mentions. On both valley types, the upper corner of each shingle at the cut line should be trimmed at roughly a 45-degree angle so water hitting the cut edge deflects down the valley instead of tracking sideways along the shingle joint.
The sealed cut edge is the fourth. Shingles that terminate at a closed-cut line should be set in a bead of asphalt roof cement along the cut so the edge cannot lift in wind-driven rain.
Finally, metal compatibility matters on open valleys. Aluminum flashing in direct contact with copper, or steel flashing under a copper gutter line, sets up galvanic corrosion that eats through the channel years ahead of schedule.
How Valley Type Shows Up in a Bid
Most estimates say nothing about valley method, which is precisely why the decision gets made by default in the truck rather than deliberately at the table. A bid that specifies valley type, metal gauge, and underlayment width is a signal about the contractor's standards.
When you are comparing estimates, look for the valley line and treat a missing one as a question to ask, not an omission to overlook. Two bids that appear a thousand dollars apart may simply be one crew pricing open metal and another pricing closed-cut without either one saying so.
Ask for the specification in writing as part of the scope of work. The language you want reads something like: open metal valley, 24-gauge galvanized steel, 24-inch W-profile, clip-fastened, over 36-inch self-adhering membrane.
That level of specificity does two things. It makes the bids genuinely comparable, and it gives you contractual ground to stand on if the finished work does not match what you paid for.
Inspecting Your Existing Valleys
You do not need to get on the roof to learn something useful about your valleys. From the ground with binoculars, or from an upstairs window, you can see most of what matters.
On an open metal valley, look for rust streaking, buckling or oil-canning in the channel, lifted shingle edges along the metal, and debris dams at the eave end. On a closed-cut valley, look for a dark shiny stripe down the channel, which is asphalt mat showing through where granules have scoured away.
Inside the house, valley leaks often present at an unexpected distance from the valley itself, because water that gets under the shingles travels along the decking and rafters before it finds a place to drop. If you suspect intrusion, the diagnostic steps in our guide to identifying a roof leak will help you trace it to its origin.
Remember that valleys deserve attention at every scheduled inspection, not just after a storm. A valley that is scouring or holding debris gives months of warning before it leaks, and that window is where inexpensive maintenance replaces expensive repair.
The Decision Rule
If you live in a freeze-thaw climate, have significant tree cover, have valleys longer than about 20 feet, or have roof planes of markedly different size, specify open metal and pay the difference. The added cost on a typical home with 60 linear feet of valley runs a few hundred to roughly a thousand dollars, and it buys you the assembly with the wider margin for error.
If your roof is a simple gable with short, steep, unobstructed valleys in a temperate climate, closed-cut installed correctly with full ice-and-water coverage and disciplined nail setback will serve the full life of the shingle. Either way, the point is that you chose — because the alternative is that the choice gets made for you by whichever method the crew happens to prefer.
This article is for informational purposes and is not financial, mortgage, or contractor advice. Consult a licensed professional in your jurisdiction.