Roof valley flashing installation explained

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Roof valley flashing is the material placed into the valleys formed between two opposing sloped surfaces on your roof. This material prevents water from seeping beneath the underlayment placed onto the roof decking at the valley locations.

Often used with asphalt roofing, the flashing directs the flow of water along the valleys and off of the roof's edge when installed correctly.

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Installing roof flashing is a fairly easy process. The material often comes in flat sheets shaped into a shallow V so that it runs smoothly along the two sloped edges of the valley.

These sheets are cut to fit the length of the valley and placed so that they overlap one another or are butted closely enough together that they can be joined into a single piece.

The overlap should be arranged so that flowing water falls from a higher piece of flashing onto a lower piece to prevent its seeping beneath the material. The butted pieces are usually soldered together to create a continuous surface.

Once the roof valley flashing is set into place, it is nailed down with a series of nails running along the length of the edges of the flashing. Overlapping pieces may sometimes be sealed to one another using roofing cement to prevent driving rain or snow from being forced beneath the overlapping edges.

Not all roof flashing follows the simple V design. Some flashing material is designed with a small ridge along the center to prevent water from running down one slope of the roof, crossing over the valley, and then running over the edge of the flashing located on the opposing slope. This is especially important when the two slopes cause the flow of water along the valley to run at differing speeds due to differing slope angles.

Roof valley flashing comes in a variety of material types. Some types of flashing are available in a membrane that's a bit more flexible than metal counterparts. Others come in sheets of aluminum, copper, lead, zinc and stainless and galvanized steel.

Many flashing materials come preformed with the shallow V shape. Yet they can also be purchased in an unformed state, ready for bending as needed to fit your particular home's asphalt roof slopes.

Once you know how to install roof valley flashing, you may be tempted to do it yourself. For residential roofing, however, a contractor is strongly recommended. A contractor can provide you with estimates of roofing prices involving various materials.

A contractor can also install the flashing while ensuring that the installation process will not void the roofing warranty. You can usually find an experienced roofing contractor in your area through the listings available at Reply!

The roofing cost for roof valley flashing is determined primarily by the length of flashing used as well as the flashing material employed. Once in place, however, the flashing should prove worth the cost paid as it provides you with an additional line of protection against damaging moisture, extending the life of your roof.

Photo credit: Robin Tell via Compfight CC.