Roof Valleys: How Each Type Is Built and Where They Fail
8 step by step guides
A valley is where two roof planes meet in an inside corner, and it carries the runoff from both of them. It is the busiest drainage channel on the roof, and on a house with several gables it can carry more water per foot than any other part of the roof. That is why valleys are where so many roofs leak first, and why the method you pick matters as much as the shingles.
There are three common methods. Start with open, closed-cut and woven valleys explained to see which suits your roof, then read how to prep a roof valley, because the membrane under every valley type is built the same way. From there the guides split into the open metal valley, the closed-cut valley and the woven valley.
Trouble spots get their own guides: valleys where two roof planes have different pitches, valleys that die into a wall, and how to find and repair a leaking valley. In the Fraser Valley, where valleys under firs and cedars fill with needles and moss, the open metal valley and a yearly clean out are the two best defences.
Roof Valleys Guides
- Guide 1Open, Closed-Cut and Woven Valleys ExplainedThere 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.AdvancedReading guide, 15 minutes
- Guide 2How to Prep a Roof ValleyTo prep a roof valley, strip the old roofing, repair any soft deck, and sweep the valley clean. Lay self-adhered ice and water shield centred on the valley, commonly 36 inches wide with 18 inches on each side, pressed tight into the corner. Lap sections at least 6 inches with the upper piece over the lower, run the field underlayment over its edges, and keep every nail at least 6 inches from the centreline.Advanced1 to 2 hours per valley
- Guide 3How to Install an Open Metal ValleyAn open metal valley lays W-profile or V-profile valley metal, commonly 24 inches wide with a rib about 1 inch high, over a 36 inch strip of ice and water shield. Start at the eave, lap sections 6 to 8 inches upper over lower, fasten only along the outer edges or with cleats, then snap shingle cutlines starting about 3 inches from the centre at the top and widening roughly 1/8 inch per foot toward the eave.Advanced2 to 4 hours per valley
- Guide 4How to Install a Closed-Cut ValleyIn a closed-cut valley, shingles from the first roof plane run straight across the valley and up the other side by at least 12 inches. Shingles from the second plane are laid over them, snapped and cut about 2 inches back from the valley centreline, with the upper corner clipped about 1 inch. The cut edge is bedded in a band of roof cement, and no nail goes within 6 inches of the centre.Advanced2 to 4 hours per valley
- Guide 5How to Install a Woven ValleyA woven valley interlaces shingle courses from both roof planes across the valley, alternating one course from each side, with no metal. Each shingle is pressed into the corner, extends at least 12 inches onto the opposite plane, and is nailed at least 6 inches from the centreline. It suits 3-tab and other thin shingles. Most laminated shingles are not approved for weaving because the stacked layers dam water.Advanced2 to 3 hours per valley
- Guide 6How to Handle Valleys With Unequal PitchesWhen two roof planes meet at different pitches, the valley is not a 45 degree line in plan, it is flatter than either roof, and water from the steeper plane arrives fast enough to cross the valley. Snap the centreline on the actual joint, use a wider membrane, and choose an open valley with a W-rib diverter or a closed-cut valley with the lower-pitch plane run through first and the steeper plane cut. Keep nails 6 inches or more from the centre.Professional3 to 5 hours per valley
- Guide 7How to Fix a Dead ValleyA dead valley is a valley that ends where it cannot drain cleanly, against a wall, at a dormer, or on a low or flat roof. All its water dumps at one point. Fix it by building a cricket or diverter to split the flow, running wider metal and two layers of ice and water shield up the wall, adding a kickout or end dam, and sending water out to a gutter or downpipe.Professional4 to 8 hours
- Guide 8How to Repair a Leaking ValleyTo repair a leaking valley, find the source first: clear debris, then look for nails or screws in or near the centre, rusted or pinholed metal, lifted or unsealed shingle edges and cracked shingles. Test with a hose from the top down. Small faults can be patched with a membrane or metal repair. A worn valley, open deck or stained sheathing means stripping and rebuilding the valley on the existing roof.Advanced1 to 6 hours
Also on this site
Roof Valleys: Common Questions
What is a roof valley?
A roof valley is the inside corner where two sloping roof planes meet and run down toward the eave. All the water from both planes funnels into it, so it needs more protection than the open field of the roof. That usually means a wide strip of self-adhered membrane under the roofing, plus either metal valley flashing or carefully lapped shingles on top.
Which type of roof valley is best?
For most shingle roofs in wet climates, an open metal valley sheds water fastest and is the easiest to inspect and clean. A closed-cut valley gives a cleaner look and works well with laminated shingles when built to the manufacturer's instructions. Woven valleys suit only some 3-tab and similar shingles. The best choice depends on pitch, debris and the shingle you are using.
How wide should ice and water shield be in a valley?
A common specification is a strip about 36 inches wide centred on the valley, so 18 inches lies on each side of the centreline, with 24 inches as a typical minimum. Some manufacturers and low-slope or heavy-snow conditions call for a second layer. Always check the shingle manufacturer's installation instructions for the valley method you are using.
Why do roof valleys leak?
The usual causes are nails driven into or near the valley centre, debris and needles damming water so it backs up under the shingles, cut shingle edges left unsealed, worn or punctured valley metal, and valleys that were built too narrow for the volume of water. A valley that dies into a wall or flat area adds a further point of failure.
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