Valley metal protects one of a roof’s most vulnerable areas: the channel where two slopes meet and rainwater concentrates. A properly installed metal valley helps move water toward the eaves while reducing the chance of leaks beneath shingles. The right method depends on the valley design, roofing system, metal specifications, and local requirements. This guide explains how to prepare for installation, fit and secure the flashing, weave or cut shingles appropriately, and check the finished work.
What Valley Metal Does
A roof valley is the inside angle formed where two roof planes meet. Because water from both slopes flows through it, the valley handles more runoff than many other sections of the roof. Leaves, ice, and wind-driven rain can add to the stress. Valley metal, also called valley flashing, creates a durable channel that directs water down the roof and over the eaves.
Metal flashing does not replace underlayment or properly installed shingles. It works as part of a layered roof system: the roof deck supports the materials, underlayment provides a secondary water barrier, valley metal carries concentrated runoff, and shingles shed water onto the metal. Gaps, incorrectly placed fasteners, or shingles that obstruct the channel can undermine that system.
Choose the Right Valley Design
Before buying materials, identify the valley style specified for the roof. The two common designs for asphalt shingles are open metal valleys and closed valleys. Roofing manufacturers may approve one method, both methods, or only certain combinations of flashing and shingles. The product’s installation instructions and local building requirements take precedence over generic guidance.
| Valley style | How it works | Important consideration |
|---|---|---|
| Open metal valley | Shingles stop short of the valley center, leaving a visible strip of metal exposed. | The channel must remain clear, and the metal’s width and profile must suit the roof and expected water flow. |
| Closed-cut valley | Shingles from one roof plane cross the valley; shingles from the other plane are cut back to form a defined channel. | The cut edge and fastening pattern must follow the shingle manufacturer’s details. |
| Woven valley | Shingles from both slopes overlap in an alternating pattern through the valley. | Not all asphalt shingles or roof pitches are suitable for weaving; confirm manufacturer approval. |
Open valleys are often selected when a visible metal channel is desired or when roof geometry makes a closed detail impractical. Closed-cut valleys create a shingle-covered appearance, although a properly formed channel still directs water beneath the shingles. A woven valley can be difficult to execute neatly and may not be allowed for some laminated or architectural shingles. There is no single method that fits every roof.
Select Suitable Metal and Underlayment
Valley flashing is commonly made from galvanized steel, aluminum, or copper. The best choice depends on the roofing system, exposure, budget, and compatibility with nearby materials. Metal thickness, coating, and dimensions matter as much as the metal type. Follow the flashing manufacturer’s specifications and applicable code; do not assume a particular gauge or width is suitable for every installation.
Use a corrosion-resistant material appropriate for the roof environment. Dissimilar metals can corrode when they contact one another, especially where moisture is present. Check compatibility among the valley metal, fasteners, drip edge, gutters, and other roof components. Use fasteners recommended for the flashing material and roofing assembly. Avoid relying on sealant as a substitute for correct metal laps or fastening.
Install the underlayment required by the shingle and flashing instructions. Many roof assemblies use a self-adhered membrane in valleys as additional protection, but the product, placement, and width should match the project specifications and local requirements. The surface must be clean, dry, and prepared as the membrane manufacturer directs. Underlayment should be integrated with the surrounding roof layers so water is directed outward rather than behind the flashing.
Tools and Materials
Typical supplies include valley flashing in the specified profile, approved underlayment, compatible roofing nails or other specified fasteners, asphalt shingles, a chalk line, measuring tape, roofing knife, tin snips, hammer, and a straightedge. A hand seamer may be needed to shape certain metal profiles. Use only products intended for roofing applications and follow their safety and installation instructions.
Roof work presents serious fall, heat, and tool hazards. A roof should not be worked on when wet, icy, windy, or otherwise unsafe. Fall-protection equipment, stable ladder setup, appropriate footwear, and a clear work area are essential. Anyone unsure how to work safely at height or handle the roof’s materials should hire a qualified roofing contractor.
How to Install Valley Metal on a Shingle Roof
Inspect and prepare the roof
Confirm the roof pitch, valley layout, decking condition, and location where the valley meets the eave. Look for soft, damaged, or uneven decking and repair it before covering the area. Remove debris and check that the roof planes are ready for underlayment. If the project is a repair, identify the source and extent of the leak; replacing visible metal alone may not correct damage to the deck or surrounding shingles.
Install the valley underlayment
Apply the specified valley membrane or underlayment over the roof deck, following the product directions for surface preparation, overlap, and placement. Extend it far enough onto both roof planes to cover the area required by the roof design. Integrate it with the field underlayment in the correct sequence so laps shed water downhill. Avoid wrinkles, fish mouths, and open seams that can create pathways for water.
Measure, position, and cut the flashing
Measure the valley from the eave to the upper end, allowing for the required overlaps and any end shaping. For long valleys, use sections sized and lapped according to the flashing manufacturer’s details. Position the metal centrally in the valley, keeping its edges aligned with the roof geometry. If the flashing includes a raised center rib or formed channel, orient it as specified.
At the eave, the flashing should deliver water onto the intended drainage surface rather than behind the fascia or under the roof edge. Shape the lower end to suit the drip-edge and gutter detail. At the top, fit the metal beneath the appropriate upslope roofing layers so water from above flows onto it. The exact sequence can vary with the roof assembly, so follow the approved detail rather than improvising.
Fasten the flashing correctly
Fasten the valley metal only where the product instructions specify. Many systems keep fasteners away from the central water channel and locate them near the outer edges, where shingles will cover them. Nails driven through exposed portions of a valley can create leak points. Do not overdrive fasteners or leave metal loose, and do not add extra nails simply because a piece seems to move before the surrounding roof layers are complete.
Where flashing sections overlap, use the required direction and overlap dimension so the upper section sheds water onto the lower section. Secure the pieces as directed without creating a raised obstruction or an opening at the joint. If a design calls for a sealant or other treatment, use only the specified product and application. Sealant cannot correct a reverse lap or misplaced fastener.
Install shingles for an open valley
For an open valley, install shingles on both roof slopes while maintaining the specified exposed metal channel. Snap chalk lines to mark the cutback or exposure boundaries, keeping the channel straight and consistent. Cut shingles with a sharp roofing knife and a suitable cutting surface; take care not to damage the flashing or underlayment. Trimmed shingle corners may be cut as directed to encourage water flow, but the required shape depends on the shingle instructions.
Keep shingle nails outside the valley’s exposed waterway and within the permitted nailing area. Nails too close to the channel may be exposed or struck by runoff. Shingles should lie flat and should not leave a gap that exposes unnecessary underlayment beyond the design. Maintain the required channel width from the eave to the top; a narrowing or uneven channel can collect debris and disrupt drainage.
Install shingles for a closed-cut valley
For a closed-cut valley, one roof plane is generally shingled through the valley, while shingles on the intersecting plane are laid over them and cut along a marked line. The order of the roof planes matters, and installers commonly choose the slope with the greater water flow or more prominent roof plane for the continuous run. Follow the shingle manufacturer’s layout and valley instructions.
Use a straightedge to guide the cut and protect the shingles beneath it from the knife. Keep the cut line straight and positioned as specified, leaving the designed valley channel unobstructed. Do not place fasteners in the prohibited area near the valley. The final cut edge should be secure and neat; any required corner trimming or adhesive should follow the product instructions. A closed-cut valley still depends on correctly installed valley flashing below the shingles.
Finish the ridge and eave details
At the upper end of the valley, make sure the flashing and underlayment are integrated with the roof layers above. At the bottom, confirm water drains into the gutter or beyond the eave as intended. Check that shingles, starter materials, drip edge, and valley metal meet without blocking the water path. Roofing details at dormers, chimneys, and other intersections may require additional flashing that must be integrated with the valley.
Common Installation Mistakes to Avoid
- Using an unapproved valley method: A woven, cut, or open valley may not be permitted for every shingle product or roof pitch.
- Putting nails in the water channel: Fasteners in exposed, high-flow areas can become leak points.
- Reversing a metal lap: Upper sections must drain onto lower sections, not behind them.
- Leaving the channel too narrow or irregular: Shingle edges can obstruct runoff and trap debris.
- Skipping underlayment or ignoring its instructions: Valley metal is one part of a layered water-management system.
- Mixing incompatible metals or fasteners: Material incompatibility can accelerate corrosion.
- Using caulk to mask poor workmanship: Sealant is not a substitute for correctly shaped, overlapped, and fastened flashing.
Inspection and Maintenance
After installation, inspect the valley from a safe location. Look for an even channel, flat shingles, properly covered fasteners, sound laps, and clear drainage at the eave. Confirm there are no exposed nail heads, open cuts, lifted metal edges, or debris lodged in the channel. Any questionable detail should be corrected before the roof is exposed to heavy rain.
Periodically remove leaves and other debris from valleys, particularly below overhanging trees. Inspect after severe weather and when checking the roof for other maintenance issues. Avoid scraping or walking on metal unnecessarily, since this can damage the finish or surrounding shingles. Repairs should preserve the original roofing system’s approved details and use compatible materials.
Codes, Manufacturer Instructions, and Professional Help
Roofing requirements can vary by location and by the specific products used. The International Residential Code includes provisions for roof coverings and flashing, but jurisdictions adopt and amend codes independently. Local building departments can clarify applicable requirements. The shingle and flashing manufacturers’ current installation instructions are also essential, especially for valley type, underlayment, fastening, metal dimensions, and roof-pitch limitations.
A licensed or otherwise qualified local roofing contractor can assess complex valleys, steep or high roofs, concealed water damage, and repairs involving multiple roof intersections. A contractor should explain the proposed valley method, materials, and how the detail complies with product instructions and local requirements. For further guidance, consult the International Code Council for code information, the National Roofing Contractors Association for roofing resources, and the specific roofing manufacturers’ installation documents.