Installation
How to Shingle a Valley
A valley carries more water per foot than anything else on a steep-slope roof. Two planes converge and everything landing on both funnels into one fast-moving line, often carrying ice and pine needles with it. It is the highest-volume, highest-velocity detail on the roof.
There are three ways to shingle one. The lining underneath matters more than the choice between them, and the dead-nail zone matters more than either.
The lining goes in first, whatever method follows
Before any method, the valley gets a self-adhered membrane centered in it, full width, eave to ridge, rolled tight into the crease. Bridging is the failure — a membrane spanning the angle instead of following it tears the first time somebody walks the valley or ice loads it.
Run it before the field underlayment, then lap the field sheets over its edges so water crossing the boundary stays on top. In an ice climate this is also the ice-barrier layer, and it wants to be wide.
- ●Membrane — the universal base layer. Centered, full width, fully adhered, no bridging.
- ●Metal liner — required for an open valley, optional as a belt-and-braces layer under a closed-cut one. It sits on top of the membrane.
- ●Rolled underlayment liner — a strip of smooth roll roofing centered in the valley, historically used under woven and closed-cut valleys and still specified by some manufacturers. A slip and wear layer, not a waterproofing one.
Open valley
Metal-lined, with the shingles cut back on both sides so a channel of exposed metal runs down the middle. It is the most watertight of the three and the most expensive.
- 1
Set the metal
W-profile metal has a raised rib down the center; flat metal does not. The rib matters where the pitches or contributing areas are unequal, because it stops water shooting across the channel and up under the far side. Common widths run 20 to 24 inches. Hem both outer edges — the hem stiffens the run and makes a turned lip that resists capillary draw at the shingle edge.
- 2
Fasten with cleats, not face nails
Clips or cleats along the outer edges, nailed beside the metal and folded over the hem, so the metal is held without a hole in it. Face-nailing through the pan locks a run that has to move, buckles it, and puts fasteners in the wettest part of the roof. Lap upslope over downslope, generously, and set laps in sealant.
- 3
Snap diverging chalk lines
Two lines, one each side of the centerline, narrow at the ridge and widening as they descend — commonly about 3 inches either side at the top, widening roughly an inch every 8 feet. The channel grows as the volume grows. Parallel lines look tidier and choke the valley exactly where flow is highest.
- 4
Cut to the line and clip every corner
Run the shingles through and cut them back to the chalk. On every cut shingle take a 45-degree clip off the upper corner, the one pointing up the valley. That clip throws water into the channel instead of letting it run along the cut edge and up into the joint between courses. One second per shingle.
- 5
Seal the last couple of inches
A bead of asphalt roof cement under roughly the last 2 inches of each cut shingle sets the edge down on the metal, so wind cannot lift it and capillary action cannot pull water sideways. Thin bead — a heavy one squeezes out and shows.
Closed-cut valley
One plane runs continuously through the valley and onto the adjoining roof; the other is shingled over it and cut back near the centerline. No metal shows. This is what most residential roofs get.
The through-run extends at least a foot past the centerline onto the adjoining plane, so a full shingle body — not a lap — lies under the cut. The cut side is trimmed back roughly 2 inches from the centerline, which puts the cut on top of continuous shingle rather than on a joint. Clip the 45-degree corner on every cut shingle as in an open valley, and set the last 2 inches in cement.
Which plane runs through?
The governing principle is not in dispute: all the water on the cut side crosses onto the through side, so the through side must be continuous unbroken shingle under the entire cut, and no fastener may sit near the centerline where that crossing water travels.
Which plane runs through is disputed. One convention runs the lower-volume plane through, so the plane delivering the most water is the one being cut and its flow lands on continuous material. Another runs whichever plane is larger. Regional practice differs and manufacturers print different instructions. Settle it with the printed instruction for the shingle in your hands, not a rule of thumb — the warranty follows that document.
Woven valley
Courses from both planes alternate across the valley, each running through and lapping onto the opposite roof. No cutting, no metal, a continuous shingle surface through the crease.
It has fallen out of favour for three honest reasons. Heavy architectural laminates are stiff and thick and will not lie flat through the bend — they bridge, and a bridged shingle waits to crack across the fold or get stepped through. Many manufacturers now prohibit weaving their dimensional products outright, which ends the discussion on a warrantied roof. And it is slow: every course carried across by hand, with the two planes unable to run independently.
On 3-tab it still works, and there are decades of woven 3-tab valleys performing fine. On a laminate, check the wrapper first.
The dead-nail zone
Nothing within about six inches of the centerline
Every fastener in a valley is a hole in the fastest water path on the roof. Keep all nails at least six inches back from the centerline on both planes, further on a high-volume valley. Where a shingle needs holding closer than that, hold it with cement.
A nail near the centerline does not leak immediately. It leaks in year four, after the hole works oval from thermal movement, and it shows up inside at a point nowhere near the valley. One of the hardest leaks to trace, which is why the rule is worth being religious about at install time.
The three methods, compared
| Open (metal) | Closed-cut | Woven | |
|---|---|---|---|
| Watertightness | Best. A continuous metal channel carries the flow; the shingles never have to. | Good when the cut geometry and dead-nail zone are respected. Entirely workmanship-dependent. | Good on 3-tab, unreliable on laminate because the shingle bridges instead of seating. |
| Labor | Highest. Metal fabrication, cleats, two chalk lines, cut and clip both sides. | Lowest. Run one plane through, cut the other. | High. Every course crossed and set by hand, and the planes cannot run independently. |
| Debris | Self-cleaning. Smooth metal sheds needles and grit that a granulated surface holds. | Holds debris along the cut edge. Pine needles pack in and dam the valley. | Holds debris across the whole crease. |
| Appearance | A visible metal stripe — deliberate on copper, divisive on a plain shingle roof. | Clean, uninterrupted shingle. The reason most homeowners pick it. | Uninterrupted but visibly lumpy on anything thicker than 3-tab. |
| Where it fails | Face-nailed metal, laps run the wrong way, channel too narrow at the bottom. | Nails near the centerline, missing corner clips, through-run too short. | Bridged shingles, cracked folds, manufacturer prohibition voiding the warranty. |
Method availability for any specific product is set by its printed installation instructions.
Valley length is not the run you measure on a plan — it follows the hip and valley factor, which depends on both pitches, and unequal pitches change the geometry of the cut as well as the length. Run both slopes before you order metal or lay out chalk.
Open the roof pitch calculatorWhere the rule breaks down
Two different pitches meeting in one valley
The centerline is no longer the bisector of the two planes, courses arrive at different angles, and the exposures do not line up across the valley. Closed-cut goes wrong specifically: the cut line and the real water path diverge, the through-run has to extend further to stay under the cut, and the courses will not match on the far side. Use an open valley with W-profile metal — it absorbs the geometry mismatch and the rib keeps the two flows separated.
A long steep slope dumping into a short shallow one
The worst hydraulic case on a residential roof. Water comes down the steep plane with real velocity, hits the valley, and instead of turning it shoots across and up under the shingles on the shallow side — the classic leak that only appears in a hard, driven rain. The answer is a W-profile open valley, the rib acting as a physical barrier, plus a wider channel than pitch alone would suggest. A closed-cut valley has nothing here to stop the crossing water.
A valley that dies into a sidewall instead of a gutter
Where a valley terminates against a wall — common on a dormer or an L-shaped house — the entire valley volume arrives at the bottom of that wall and, with nothing to divert it, runs down the siding and behind it. This is the detail that rots wall framing while the roof itself is fine. It needs a kickout flashing at the bottom of the step-flashing run, sized for the volume the valley is delivering rather than for an ordinary eave.
Ice damming in valleys
A valley collects snow sliding off both planes, and that pack sits longer than anywhere else on the roof. Meltwater backs up under the shingles above it, which is why the membrane run matters — up the valley well past where a dam could plausibly reach, not merely to the eave requirement. In severe climates an open metal valley also gives the melt a smooth path out rather than a granulated one to freeze into.
Wooded lots and debris
On a lot with pines or mature hardwoods, debris decides the method. Needles pack into the cut edge of a closed valley and build a dam that holds water against the shingles until it finds a way sideways. An open metal valley self-cleans in ordinary rain. Where trees overhang the roof, this outweighs the appearance argument.
Metal choice and galvanic pairing
Valley metal is commonly painted steel or aluminum; copper appears on copper-flashed and historic roofs. If there is copper anywhere upslope — a chimney cricket, a bay roof — do not put aluminum or bare galvanized in the valley below it, because copper-laden runoff corrodes both. Match cleats and fasteners to the metal too; a steel cleat on a copper valley is the same mistake in miniature.
Closed-cut dominates for a reason, and it is not performance
Worth stating plainly. Closed-cut is faster, uses no fabricated metal, and looks the way most homeowners want a roof to look. Real advantages, and why it is the default. It is not the most watertight of the three, and a crew that says it is has confused market share with performance.
Frequently asked
Does an open valley leak more because the metal is exposed?
No — built correctly it is the most watertight of the three. The exposed metal is the drainage channel, not a weak point. What does make open valleys leak is face-nailing through the pan, laps run the wrong direction, and a channel that stays narrow all the way down.
Can I convert a closed-cut valley to an open one without redoing the roof?
Not cleanly. Cutting back existing shingles leaves you slipping metal under courses that are sealed and nailed, and you cannot get metal under the through-run without lifting it. It is a section rebuild — strip both planes back a few feet and redo the detail. Anyone offering to do it by cutting from the top is selling a repair that will leak.
How wide should the exposed channel be?
Roughly 3 inches either side of the centerline at the top, widening as it descends so the channel grows with the volume. Go wider on a valley collecting a large area, on unequal pitches, and in a snow climate. Narrower looks tidy and chokes the valley where it matters most.
Keep Reading
Diagnosis & Repair
Kickout Flashing: The Detail That Causes the Most Callbacks
Where the roof edge dies into a sidewall, why the last piece of step flashing has to be a diverter, sizing and angle, sequencing with the water-resistive barrier, and how to retrofit one without tearing off the wall.
Installation
How to Install Drip Edge (and Where Gutter Apron Beats It)
Eave-first or underlayment-first, the difference between a D-style drip edge and a gutter apron, hem orientation, lap direction, fastener spacing, and the rake detail that lets wind pull the whole run off.
Installation
How Many Nails Per Shingle? The Real Answer
Four versus six, where the nail line actually is on a modern laminate, what high-nailing does to wind performance, penetration depth, and why the warranty and the code can require different counts on the same roof.
Diagnosis & Repair
How to Find a Roof Leak: A Diagnostic Walkthrough
Working backwards from the stain: interior mapping, the attic inspection, the penetration checklist, the water test done in the right order, and how a flat-roof leak differs from a steep-slope one.
On code citations: section numbers here refer to the model International Residential Code. Your jurisdiction adopts a specific edition and routinely amends it, and manufacturer installation instructions are enforceable alongside it — where the two differ, the stricter one generally governs. Confirm anything load-bearing with your building department and the printed instructions in the bundle wrapper before you rely on it.
Need a Contractor Who Knows This Detail?
Search roofing companies by city or state, read their Google reviews, and request quotes directly. Listings are compiled from public records — confirm any license and insurance with your state board before work begins.