Rolled Valley

Rolled valley is the metal that lines the valley of a roof — a continuous metal strip used to line roof valleys, creating a channel that directs water away from roof joints and off the deck. It ships as a coil, gets cut to length on site, and forms the waterproofing surface in the single hardest-working spot on any roof. Two roof planes meet at a valley, and the water from both panels will funnel into the valley, which is why proper installation is crucial. A valley leak isn’t a nuisance — it’s the leak that rots the deck.

For related product information, see Metal Roof Closures and Mastic: How to Seal a Metal Roof Right.

For a Montana re-roof or new build, the buying decision comes down to two things: get the metal right, and get the gauge right. Everything else follows from there.

Material and Gauge — The Decision That Matters Most

Pick the metal for the climate and the life you want out of the roof. Galvanized steel is affordable, while Galvalume or aluminum offers superior corrosion resistance for coastal or high-flow areas. Aluminum brings its own advantage — it’s naturally rust and corrosion resistant, though it’s softer and dents easier than steel under debris or a boot.

The galvanized coating earns its keep. On heavier-gauge steel, the galvanization process applies a protective zinc coating that delivers excellent resistance to rust and corrosion, ensuring the flashing maintains its integrity and effectiveness over decades of exposure to the elements.

Now the gauge. This is where cheap roofs die early. Select a minimum 24-gauge thickness, as 28-gauge is prone to denting and early failure. A heavier gauge isn’t just about rust resistance — the thickness provides superior strength and rigidity, making it highly durable and resistant to damage from debris or foot traffic during installation. In a climate that piles snow loads of 50 to 80 psf on the valley and runs freeze-thaw cycles all winter, thin metal is a false economy.

Sizes, Widths, and Types

Western Building Center stocks rolled valley and roll flashing in galvanized, aluminum, brown, and black/gray, across the widths and lengths that match most valley runs:

Type	Widths Carried	Lengths Carried
Galvanized flashing	10”, 14”, 20”	10’, 25’, 50’
Aluminum flashing	10”, 20”	10’, 50’
Brown flashing	10”, 14”, 20”	10’, 25’, 50’
Black/gray roll valley	14”	50’

Match the width to the volume of water the valley carries. Wider rolls earn their place on the harder runs — the increased width, compared to narrower options, offers enhanced coverage in the valley, making it particularly well-suited for roofs with steeper pitches or longer valley runs where a greater volume and velocity of water is anticipated.

Length matters too. Go long on long valleys. The 50-foot roll minimizes the number of seams required in the valley, further reducing potential leak points and streamlining the installation process. Fewer seams, fewer chances to leak.

Beyond standard roll valley, a couple of specialty types exist for specific roofs. Ribbed or W-profile valley metal serves tile roofs — it comes in various center diverter heights, with 1-inch or 1.5-inch versions used with concrete, clay and slate tiles on slopes from 2½:12 to 24:12, and a 3.5-inch center used where one roof plane carries a greater anticipated amount of water flow, typically where two planes joining in a valley are significantly different slopes or sizes. For low-slope work there’s also an asphalt valley-seal membrane — a glass fiber reinforced sheet sandwiched between two layers of polymer modified bitumen that lays flat, resists wrinkling, and is easier to work with than metal or peel-and-stick materials.

Installation Basics

Valley installation is a sequence. Skip a step and you’ve built a leak path. The order is not negotiable.

Waterproofing goes down first, metal on top. Apply a waterproof underlayment first, center the metal, and overlap sections by at least 6 inches, sealing seams with butyl or urethane sealant to prevent leaks. The overlap direction is the whole game — upper section over lower, so water runs over the seam and never into it.

Fasten at the edges only. On ribbed valley metal the rule is explicit: do not penetrate anywhere other than the outside nail flange, fastened minimum 12 inches on each side with corrosion resistant roofing nails, and all nail fasteners through the nail flange should be sealed. Same principle on open metal shingle valleys — they perform better because they don’t require as much nailing in the valley; roofers should nail only at the edges of the flashing, which is far enough from the center of the valley to be safe. A nail in the center channel is a leak waiting on the first hard rain.

Where joints lap, hold the overlap. Lap valley metal joints a minimum of 6 inches. And keep them clear after the fact — to prevent foliage or debris from damming water in the valley, regular maintenance may be required, and any obstruction should be removed to prevent water dams that could damage the roof system.

Open vs. Closed Valley — What Snow Country Demands

Whether you even need rolled valley metal depends on the method. There are three main types: woven, closed-cut, and open. Closed-cut and woven valleys use shingles alone and need no metal. Open valleys use the exposed metal flashing.

For Montana, the open metal valley wins. Open metal roof valleys provide great performance, especially when it comes to shedding snow and avoiding debris build-up. That’s the whole argument right there — a valley that sheds snow and ice instead of holding it. Woven valleys carry the opposite problem in cold weather: they’re challenging to install with laminate shingles, which are stiffer and thicker than 3-tab and likely won’t bend enough to weave in neatly, especially not in cooler climates, which is why woven valleys are not recommended by most laminate shingle manufacturers.

The open metal valley costs more and takes more skill. It may be more expensive than other types — the roofer has to choose, buy and bring flashing to the job, lay chalk lines, cut the flashing, secure it, and cut many shingles. Worth it on a roof that has to survive snow load and ice damming.

One warning that costs nothing to heed: some manufacturers require a specific roof valley installation to be covered by their warranty. Check the shingle warranty before you pick the method.

Frequently Asked Questions

What gauge should rolled valley be for a snow climate? A minimum of 24-gauge. Thinner metal like 28-gauge dents under foot traffic and fails early, and heavier gauge gives the strength and rigidity to resist damage from debris and boots during installation — the difference between a valley that outlives the shingles and one that rusts through ahead of them.

Galvanized, aluminum, or Galvalume — which valley metal is best? Galvanized steel is the affordable workhorse, and its zinc coating resists rust and corrosion for decades. Galvalume and aluminum offer superior corrosion resistance for high-flow areas. Aluminum won’t rust at all but is softer and dents more easily under debris.

Why does an open metal valley make sense in Montana? Because it sheds snow and ice faster and avoids debris build-up, where woven and closed-cut shingle valleys can hold water. Open metal valleys also need less nailing in the valley itself, keeping fasteners away from the channel where leaks start.

How much should valley sections overlap? At least 6 inches, upper over lower, so water flows across the seam rather than into it. Seal the seams with a butyl or urethane sealant. On longer runs, a 50-foot roll cuts down the seam count and the leak points along with it.

Where do you nail rolled valley? Only at the outer edges — never in the center channel. A center fastener is a guaranteed leak. On ribbed valley metal, fasten through the outside nail flange a minimum of 12 inches on each side, with corrosion-resistant nails, and seal every fastener.

How wide a roll do I need? Match width to water volume. Standard runs do fine on narrower stock, but steeper pitches and longer valleys carry more water at higher velocity and call for a wider roll for the extra coverage.