Open, Closed-Cut and Woven Roof Valleys: How They Differ and Which to Use
Three ways to build the same inside corner, and the trade-offs that decide which one belongs on your roof.
- Advanced
- Reading guide, 15 minutes
- Updated
The short answer
There are three common shingle valley methods. An open valley exposes a strip of metal flashing between the two shingle edges. A closed-cut valley runs shingles from one side straight across and trims the other side back about 2 inches from the centreline. A woven valley interlaces shingle courses from both sides. Open metal valleys shed water fastest, closed-cut suits most laminated shingles, and woven suits only some 3-tab products.
Every valley has two jobs: carry the combined runoff of two roof planes down to the eave, and stay watertight while it does. The three common methods do this in different ways, and each one trades something. The open valley sheds water fastest and is easiest to clean, at the cost of showing metal. The closed-cut valley hides the metal and keeps a clean line, but is slower to build and depends on good shingle cutting. The woven valley uses no flashing at all, which is also its weakness.
Which method is right depends on the shingle, the pitch, the amount of water and the debris load. The shingle manufacturer's installation instructions, printed on the wrapper and in the technical bulletins, list which valley methods are approved for that product, and using an unapproved one can void the shingle warranty. In the Fraser Valley, where valleys under firs, cedars and maples collect needles and moss for months of the year, the choice is often made by how well the valley will drain when it is neglected.
All three methods share the same foundation: a wide strip of self-adhered membrane centred on the valley and kept free of nails near the middle. See how to prep a roof valley for that shared layer, then use this guide to choose the method.
Tools
- Tape measure
- Chalk line
- Hook blade utility knife
- Tin snips (straight cut)
- Roofing hammer or coil nailer
Materials
- Self-adhered ice and water shield, 36 inch wide roll
- Prefinished or galvanized W-valley or V-valley metal for open valleys
- Roofing nails, 1-1/4 inch
- Asphalt roof cement, for sealing cut edges
- Shingles with valley instructions on the wrapper
Safety first
- Valleys are where two roof planes meet, so footing is tight and debris-covered. Wet needles and moss make a valley as slick as ice, so work tied off with a roof anchor whenever the eave is 3 metres (about 10 feet) or more above grade.
- Valley metal and cut shingle ends are sharp. Wear cut resistant gloves when handling W-valley metal and snapping it to length.
- Never walk in the valley centre on metal flashing. It dents, it is slippery, and stepping there damages the very detail you are building.
Step by Step
Step 1: Identify the pitches and the water load
A valley that collects a large roof plane on a steep pitch runs fast and deep at heavy rain. Water from a 10/12 plane can shoot across the valley and climb under the shingles on the opposite side if the valley is too narrow or has no diverter. Big, steep, high-volume valleys favour an open metal valley with a W-rib or a wide V.
Low pitches below about 4/12 run slowly and hold water and debris longer. Most manufacturers limit or exclude closed-cut and woven valleys on low slopes, so check the wrapper before choosing. Where the two planes have different pitches, read how to handle valleys with unequal pitches as well.
Step 2: Check what the shingle manufacturer approves
Most laminated architectural shingles are approved for open and closed-cut valleys, and many manufacturers specifically say not to weave them, because two or three layers of thick laminate stack up over the valley and create a dam. Traditional 3-tab shingles are the ones most often approved for weaving.
If the wrapper lists a minimum metal width, a cutline distance or a nail setback, those numbers replace any rule of thumb in this guide.
Step 3: Consider an open metal valley first
The metal is typically 24 inches wide, with an inverted W rib of about 1 inch running down the centre that stops water from one plane surging across onto the other. Shingle cutlines are snapped about 3 inches either side of the centreline at the top and widen toward the eave, so the open channel widens as the water volume grows. The full build is in how to install an open metal valley.
Open valleys are the most forgiving in a wet climate. Needles and leaves can be swept out, water moves fast, and nothing sits against the shingle edge. The downside is appearance, and that metal edges need to be kept clean of nails and punctures.
Tip: On a roof under conifers, pick an open valley. A closed-cut valley can trap a mat of needles against its cut edge that stays wet for months.
Step 4: Consider a closed-cut valley for a clean look
The first plane's shingles lap 12 inches or more onto the other side. The second plane's shingles are cut along a chalk line about 2 inches from the centreline, with the upper corner clipped so water does not get driven under it. The cut edge is bedded in a band of roof cement. The result is a solid line of shingle with no exposed metal.
This method is widely approved for laminated shingles, and it is the usual choice when appearance matters. It depends on good cutting and on the membrane underneath, because if the cut edge leaks there is no metal to catch it. The build is covered in how to install a closed-cut valley.
Step 5: Consider a woven valley only where it is approved
Shingles from each plane run across the valley alternately, one course from the left, then one from the right, pressed firmly into the valley and nailed well away from the centreline. There is no metal, and every course has multiple layers of shingle across the valley.
It is quick with thin shingles and gives a double layer of protection. With laminated shingles it creates a thick ridge that can dam water, and it is rarely approved. See how to install a woven valley for the method and its limits.
Step 6: Weigh the maintenance and inspection difference
With an open valley you can see a pinhole, a rusted seam or a debris dam at a glance. With a closed or woven valley, the failure point is buried under shingles and only shows up as a stain on the ceiling. That matters in a neglected house where the roof is rarely looked at.
If the roof is hard to reach or the owner will not clean it, favour the open valley, and plan on sweeping it at least once a year. For repair work on an existing valley see how to repair a leaking valley.
Step 7: Choose and build the membrane the same way for any type
The self-adhered membrane is the real waterproofing layer under every valley type. It should be centred on the valley, pressed into the corner without bridging, and kept free of fasteners near the centreline. Full instructions are in how to prep a roof valley.
If the valley ends at the bottom in a gutter, a wall or a flatter roof, the detail changes at the bottom. See how to fix a dead valley for the ends that most often fail.
Quick Comparison
- Open metal valley: fastest drainage, easiest to clean, best for conifer debris and heavy rain, shows a strip of metal, works with nearly all shingles.
- Closed-cut valley: clean look, widely approved for laminated shingles, depends on cutline and sealed edge, slower to build, hides problems.
- Woven valley: no metal, fast with 3-tab, only for products approved for weaving, builds up thick and can dam water with laminated shingles.
Fraser Valley Notes
Needle and leaf debris is the main reason valleys fail here, because it keeps the valley wet long after the rain stops and feeds moss. Steeper planes help, but a neglected valley under a fir will still hold a layer of debris. Plan for a yearly clean out as part of clearing debris from the roof, and choose the open valley wherever trees overhang the roof.
Common Mistakes
- Choosing the method by looks alone. A closed-cut valley under a big fir will fill with needles and rot at the cut edge while an open valley would have stayed clean.
- Weaving laminated shingles. Most manufacturers prohibit it because the stacked layers dam water and the valley leaks at the seams.
- Ignoring the manufacturer's approved methods. Using a method the wrapper does not list can void the shingle warranty.
- Skimping on the membrane. A valley with only felt underneath relies on the top layer to be perfect. A wide self-adhered strip is the real barrier.
- Nailing near the centreline. Any nail within about 6 inches of a valley centre is a potential leak, whichever method is used.
When to Call a Professional
If the valleys are on a steep roof, run into a wall or a lower roof, carry two very different pitches, or sit under heavy tree cover, valley work is best left to a roofer. The failure points are hidden and a wrong method can leak within a single season.
If you are replacing a valley on an existing roof and the old valley is leaking, a roofer can open it up, check the deck and membrane underneath and choose the method that suits the actual water load.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
Open, Closed-Cut and Woven Valleys Explained: Questions
What is the difference between an open and a closed valley?
An open valley has a strip of metal flashing left exposed between the shingle edges, so water runs down the metal. A closed valley covers the valley with shingles. Closed-cut valleys run one plane's shingles across and trim the other plane about 2 inches from the centreline. Woven valleys interlace courses from both planes. Open valleys drain fastest and are easiest to inspect.
What is a California cut valley?
A California cut is another name for a closed-cut valley. Shingles from one roof plane are run across the valley onto the other plane, and the shingles from the second plane are trimmed along a chalk line near the centreline and laid over the first. Only shingles that the manufacturer approves for this method should be used, and the cut edge should be sealed.
Can you weave architectural shingles in a valley?
Most manufacturers say no. Laminated shingles are thick, and weaving stacks several layers across the valley, which creates a raised ridge that can dam water and stops the shingles from lying flat and sealing. Traditional 3-tab shingles are the products most often approved for a woven valley. Always read the valley instructions on the shingle wrapper.
Which valley type is best for a rainy climate?
An open metal valley is generally best in wet climates, especially under conifers. It moves large volumes of water quickly, the W-rib stops water surging across to the far side, and it can be seen and swept clear of needles. A closed-cut valley also performs well if the cut edge is sealed and the valley is kept clear.
How long does a roof valley last?
Valley life depends on the method, the metal and the maintenance. Prefinished steel or copper valley metal can outlast the shingles next to it. A closed or woven valley is only as durable as its shingles and membrane. Debris dams, nails near the centreline and worn metal shorten the life of any valley, so inspect valleys whenever the roof is inspected.
Related Guides
All Roof Valleys guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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