Roof Valleys: Open, Closed-Cut, and Woven Valleys Compared

A roof valley is the channel where two slopes meet, and it carries the runoff of both, so the method used there matters. Open valleys leave a lining exposed down the center, closed-cut valleys run one side’s shingles across and trim the other side’s along a line, and woven valleys interlace both sides; your shingle maker’s installation instructions decide which methods are allowed for your product.

No method wins everywhere. What decides whether a valley stays dry is whether its lining and laps follow those instructions, and which method fits your roof depends on the shingle, the debris load from nearby trees, and how easily you want it repaired later.

Why Valleys Carry More Risk Than the Open Field

Of all the roof components that handle water, a valley is the one that gathers it from two directions. On the open field of a roof, each shingle handles the rain that falls on it and the water from the courses above. In a valley, water from two whole slopes gathers into one channel. It runs deeper there than on the open field, and because the valley line is less steep than the slopes that feed it, the water also moves more slowly. Anything that slows it further (a pile of leaves, a ridge of ice, a lifted shingle edge) can make it back up sideways under the shingles.

Debris makes it worse because valleys collect it. HUD’s Residential Rehabilitation Inspection Guide names debris-clogged valleys as a roof condition for inspectors to check. A clogged valley acts like a small dam, and the water it holds finds every gap in the laps.

All that water also lands in one spot at the eave. The gutter at the bottom of a valley takes a concentrated stream, so it can overflow before the rest of the gutter run does, and it is worth watching from the ground.

Open, Closed-Cut and Woven: How Each Is Built

All three methods start with a lining laid in the valley before any shingles go on. Seattle’s residential code, Chapter 9, the city’s adoption of the International Residential Code (IRC), keeps the model code’s section R905.2.8.2: “Valley linings shall be installed in accordance with the manufacturer’s instructions before applying shingles.” Your building department can confirm the version in force where you live. The methods differ in what happens on top of that lining.

Open valley. The lining, metal in the code’s description of open valleys, stays visible down the center of the valley. Shingles from both slopes stop short of the centerline and are trimmed along each side, leaving an open channel. Under the same code section, an open valley lined with metal needs a lining at least 24 inches wide.

Closed-cut valley. Shingles from one slope run across the valley and onto the other slope. Shingles from the second slope are then laid over them and trimmed along a straight line near the center. No metal shows; you see one side’s shingles cut in a clean line over the other’s.

Woven valley. Shingles from both slopes are laid across the valley in alternating courses, so they interlace down its length. No metal shows and there is no cut line.

Which of these your roof can have is not a matter of taste alone. Shingle makers publish valley instructions for each product, and those instructions say which methods are allowed and how each must be done. Ask whether weaving is allowed for the exact shingle in your quote rather than assuming it is or isn’t.

Valleys also form wherever a new section of roof meets an old one, such as an addition or porch. Those transitions have their own matching and layering questions, covered in joining a new roof to an old one.

Metal or Shingle in the Valley: The Tradeoffs

The real choice is whether the water in the valley runs on exposed lining or on shingles.

Exposed metal (open valley). Water runs on a smooth, continuous surface down the center, with no shingle edges in its path. The metal shows, which some owners like and some do not, and the metal has to be compatible with the other metals on the roof and suited to the local exposure; other flashing types covers corrosion and metal choice. The trimmed shingle edges along each side are the details to inspect.

Shingles in the valley (closed-cut or woven). The valley looks continuous with the roof, and the shingles themselves carry the water over a hidden lining. In a closed-cut valley, the cut line and the shingles running underneath it are where the work concentrates. In a woven valley, both sides are interlaced, so the shingles in the center bend across the valley’s fold.

Three factors settle it:

1. The shingle maker’s instructions. If a method is not allowed for your product, it is off the table.
2. Debris. Under heavy tree cover, ask each bidder how their method sheds leaves and needles, and plan on valley cleaning either way.
3. Repairability. If you expect to replace damaged shingles near a valley, an open valley lets the repair stay on one side; a closed-cut valley does so only on its cut side, since the through side runs underneath.

Be wary of any bidder who ranks the methods in absolute terms. Each one works when it is built to the instructions, and each one fails when it is not.

What Goes Under the Valley

The lining is the valley’s real water barrier, and the code gives two routes for it. Section R905.2.8.2, as adopted in Seattle, describes metal linings for open valleys and also permits “Self-adhering polymer-modified bitumen underlayment complying with ASTM D1970” as a valley lining. D1970/D1970M-25, the edition ASTM marked active in December 2025, is the specification for that material; the 2021 edition’s scope describes it as self-adhering sheet “intended for use as underlayment on roof eaves,” where it bonds to the deck.

In cold climates, the valley is also a place where ice and backed-up meltwater collect, and the ice barrier at the eaves has its own code reach rule; how far it must extend and where it helps beyond the eaves is covered in ice barrier in valleys and at the eaves.

The field underlayment on each slope has to lap correctly with the valley lining so water on the underlayment ends up on top of the lining, not under it. Which field underlayment to request is covered in field underlayment.

Ask each bidder to name, in writing:

• The valley method
• The lining material and its width, or the standard it meets if it is a self-adhered membrane
• Whether the lining goes down before the field underlayment or after, per the shingle maker’s instructions
• Whether a cold-climate ice barrier extends into the valleys

How Valley Failures Show Up

Valley problems show at the surface and in the attic, and the surface signs can be seen without leaving the ground. Home inspectors following the InterNACHI Standards of Practice, last revised October 2022, inspect from “ground level or the eaves,” and that is the right vantage for you too.

From the ground, with binoculars:

• Leaves, needles or granules piled in the valley
• Shingle edges along the valley that are lifted, curled or broken
• A cut line on a closed-cut valley that wanders or has pulled open
• Exposed lining that is rusted, dented or has gaps
• During a heavy rain, water overshooting the gutter where the valley drains

From the attic, with a flashlight after a rain:

• Stains or wet wood on the deck along the valley framing
• Water marks on the framing below the valley

Photograph anything you find, with dates. Other checks you can make safely from below are in safe roof checks from the ground. Have valleys checked and cleared during gutter cleaning or a professional inspection, not by walking the roof yourself.

Which Valley Method Should You Ask For?

Ask for a method your shingle maker allows for the exact product, built to its valley instructions, and named in the quote. If more than one method is allowed, choose on debris and repairability. If the maker allows an open valley and you expect to repair one slope without disturbing the other, it is the easier method to work on later; closed-cut gives that only on its cut side. Under light tree cover, any allowed method works; under heavy cover, choose the bidder who explains in writing how its method sheds leaves and needles. Whichever you choose, plan on keeping the valley clear.

If two bids use different methods, do not pick on the method name. Compare whether each names its lining, its width or standard, the lap order with the underlayment, and the shingle maker’s instructions. The bid that answers all four in writing is the one you can hold to account.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• Residential Rehabilitation Inspection Guide, U.S. Department of Housing and Urban Development, Office of Policy Development and Research
• 2021 Seattle Residential Code, Chapter 9: Roof Assemblies, City of Seattle, Department of Construction and Inspections
• D1970/D1970M-25 Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection, ASTM International
• InterNACHI Home Inspection Standards of Practice, International Association of Certified Home Inspectors