Meta description: Learn how valley tin for roofing works, which materials and styles are available, and how to install and maintain roof valley flashing.
Where two roof slopes meet, rainwater can concentrate and move quickly toward the eaves. A roof valley must channel that water without allowing it beneath the shingles or panels. Valley tin—also called valley flashing or a valley liner—is the sheet-metal component commonly used to protect this vulnerable area. Choosing the right material and installation method depends on the roof covering, local code, and the roofing manufacturer’s instructions.
What Is Valley Tin for Roofing?
Valley tin is a strip or formed section of corrosion-resistant metal installed where two roof planes intersect. The valley creates a channel that guides runoff down the roof. Depending on the roofing system, shingles or metal panels may stop short of the centerline, overlap the flashing, or meet in a concealed, woven arrangement.
Despite the name, valley tin is not necessarily made of tin. Today, the term is often used informally for galvanized steel, aluminum, copper, or another suitable flashing metal. The correct product must be compatible with the roof covering and surrounding materials. Mixing metals that can corrode when they contact each other is a common source of premature failure.
Why Roof Valleys Need Proper Flashing
Valleys receive runoff from both adjoining roof slopes, so they can carry more water than a typical section of roof. They may also collect leaves, needles, and other debris. If water is slowed by a blockage, poorly placed fasteners, or an improperly shaped channel, it can back up beneath roofing materials.
A properly installed valley liner provides a durable drainage surface beneath or alongside the roof covering. It helps protect the roof deck and directs water toward the eaves. Flashing does not compensate for poor workmanship elsewhere: the valley underlayment, roof covering, eave details, and drainage path must work together.
Common Roof Valley Styles
Open Valley
An open valley leaves a visible strip of metal exposed between the two roof slopes. Shingles or other roof materials are cut back from the channel, allowing water to flow over the valley flashing. Open valleys are often used with asphalt shingles and are also common in some metal-roof designs.
Open valleys make the metal channel visible and accessible for inspection. Their appearance depends on the flashing profile and the cut lines of the adjoining roof materials. The channel should remain wide and unobstructed enough for effective drainage, with installation details following the roofing manufacturer’s specifications.
Closed-Cut Valley
In a closed-cut valley, roofing material from one slope continues through the valley, while material from the other slope is trimmed along a line. The valley metal is largely hidden. This approach is common with asphalt shingles, but it still requires appropriate valley protection beneath the roofing materials.
Cutting and fastening must be controlled so the exposed edge does not direct water under the shingles. Installers should follow the shingle manufacturer’s instructions for the required overlap, cutback, and fastening locations.
Woven Valley
A woven valley is formed by interlacing shingles from both roof slopes across the valley. It may be suitable for some roofing products and roof pitches, but not every shingle or system permits it. A woven installation can be difficult to execute cleanly and may be less appropriate where the roof is steep, water flow is heavy, or the manufacturer specifies another method.
“Open” and “closed” describe the visible finish, not whether the valley has adequate waterproofing. The underlayment and flashing design should be selected for the roof assembly and installed according to applicable requirements.
Valley Flashing Materials
| Material | Typical advantages | Important considerations |
|---|---|---|
| Galvanized steel | Widely available, rigid, and often economical | Coating and thickness matter; damaged or cut edges may corrode. Confirm compatibility with adjacent metals. |
| Aluminum | Lightweight and naturally corrosion-resistant | Can dent or deform more easily than steel. Avoid direct contact with incompatible metals and treated materials unless approved. |
| Copper | Long-lasting and suitable for some premium or historic roofs | Higher cost; runoff can stain some surfaces. It must be compatible with connected metal components. |
| Stainless steel | Strong corrosion resistance in suitable grades | Usually more expensive; the specified alloy and fastening system should suit the environment. |
There is no single best valley tin for every roof. The choice depends on the roofing material, exposure, budget, expected service life, and compatibility with gutters, fasteners, and other flashing. Coastal locations and areas with industrial pollution may require more corrosion-resistant products. Product data and the roof-system manufacturer’s guidance should determine the final selection.
How to Choose Valley Tin
Match the Roof System
Start with the roof covering. Asphalt shingles, standing-seam metal, tile, slate, and other materials have different valley details. Some metal-roof manufacturers require a specific valley pan, clip arrangement, seam termination, or closure. A generic piece of sheet metal may not accommodate the panel geometry or movement of a particular system.
Check Code and Product Requirements
Building-code provisions and local amendments vary. In the International Residential Code, valley-flashing provisions for asphalt shingles address details such as material, width, and installation; the adopted edition and local authority determine what applies. For example, IRC provisions have specified corrosion-resistant metal valley flashing at least 24 inches wide and 0.019 inch thick in certain applications. Those figures should not be treated as a universal specification: verify the locally adopted code, roof type, and current manufacturer instructions before ordering material.
Local building departments can clarify adopted code requirements and permit rules. Roof-system instructions may impose additional details that are essential to a product warranty.
Consider Width, Shape, and Water Flow
The valley flashing must extend far enough beneath the roof covering on both sides while maintaining an effective drainage channel. Width and profile vary by roof design and manufacturer. A central crease or formed channel can help direct water, but the shape must suit the installation rather than create a raised obstruction or a place for debris to catch.
Use Compatible Fasteners and Sealants
Fasteners should be corrosion-resistant and appropriate for the flashing metal and roof assembly. Sealants are not a substitute for correct overlaps and drainage design. Some sealants can damage certain metals, roof membranes, or coatings, so compatibility should be confirmed before use.
How Valley Tin Is Installed
Valley installation is a high-consequence part of a roof and is generally best handled by a qualified roofing contractor. A typical process includes these steps, though the exact sequence varies by roofing system:
- Inspect the roof framing and deck. The valley area should be sound, properly supported, and free of damaged sheathing or protruding fasteners.
- Install the specified underlayment. Valley protection may include a self-adhered membrane or other approved underlayment. The membrane’s placement, overlap, and compatibility with the roof materials should follow the product instructions and local requirements.
- Position the valley flashing. The metal is centered over the valley and arranged to shed water toward the eaves. Sections are overlapped in a water-shedding direction, with the required overlap determined by the system and exposure conditions.
- Fasten without obstructing the channel. Fasteners are placed where the design permits and kept out of the main water path. Exposed fastener heads or poorly located nails can create leak points.
- Install the roof covering to the specified detail. The shingles or panels are cut, woven, or terminated as required. The valley must remain clear, and the roofing should not be fastened through prohibited areas.
- Check the completed drainage path. The installer should confirm that laps face downslope, edges are secure, and no debris, sealant, or material blocks the channel.
Metal expands and contracts with temperature changes. Some systems account for movement through clips, seams, or other concealed fastening methods. Rigidly fastening a component in a way that conflicts with the manufacturer’s design can cause buckling or loosened joints.
Common Valley Flashing Problems
- Fasteners in the water channel: These can create openings where water enters the roof assembly.
- Insufficient overlap or reversed laps: Water can run beneath a joint rather than over it.
- Incompatible metals: Contact between dissimilar metals in the presence of moisture can accelerate corrosion.
- Flashing that is too narrow or poorly shaped: The roof covering may not protect the edges, or water may escape the intended channel.
- Debris buildup: Leaves and needles can slow drainage and hold moisture against the roof.
- Improper repairs: Smearing sealant over a leak may conceal damage without correcting the failed flashing or underlayment.
Water stains near a valley, damp attic insulation, peeling paint, or visible corrosion can indicate a problem. Leaks may appear some distance from their entry point, so the location of an interior stain does not always identify the exact roof defect.
Maintenance and Inspection
Valleys should be checked periodically, especially after severe weather and when nearby trees shed leaves or needles. From a safe location, look for debris, lifted roofing, displaced metal, rust, and visible damage. Cleaning should not involve walking on a roof without appropriate training and fall protection. A professional inspection is safer when access is difficult or the roof is steep.
Small amounts of debris can often be cleared without disturbing the roofing, but damaged flashing or recurring leaks call for a qualified contractor. Repairs should address the underlying cause, which may include failed underlayment, improper fastening, corrosion, or an incorrectly detailed roof covering.
Valley Tin Cost Factors
Material price is only one part of the cost. The total depends on the metal type and thickness, valley length, roof pitch, roofing material, access, removal of existing layers, and the condition of the deck. Custom-formed flashing and specialty metals generally cost more than standard stock products. Labor can also rise when the valley connects to dormers, skylights, or other complex roof details.
When comparing estimates, check whether they specify the flashing material, underlayment, installation method, disposal, and repair of damaged decking. A low material price is not a useful comparison if one proposal omits necessary valley preparation or uses a detail that conflicts with the roof manufacturer’s instructions.
Frequently Asked Questions About Valley Tin
Is valley tin required for every roof?
Requirements depend on the roofing system, adopted code, and manufacturer instructions. Many roof assemblies use metal valley flashing, while some approved systems rely on specified membranes or other valley details. The complete assembly must be designed for the roof covering and local requirements.
Can old valley flashing be covered with new shingles?
Not automatically. Existing flashing should be inspected for corrosion, damage, poor installation, and compatibility with the replacement roof. Covering a failed valley can hide a leak without stopping it. A roofing professional can determine whether the flashing can remain or should be replaced.
What is the best metal for roof valleys?
The best choice is the material approved for the roofing system and compatible with adjacent components and the local environment. Galvanized steel, aluminum, copper, and stainless steel each have appropriate uses; none is ideal for every roof.
Reliable References
- International Code Council, International Residential Code — consult the edition adopted by the local jurisdiction for applicable roofing and flashing provisions.
- National Roofing Contractors Association — roofing guidance and contractor resources.
- Asphalt Roofing Manufacturers Association — asphalt-shingle installation resources and technical information.