Shingles are one of the more preferred types of roofs, since shingles are durable and fairly inexpensive. They are also fairly easy to install, although some areas of the roof, such as the roof valleys, can be challenging. Proper shingle application on roof valleys is essential in order to have a weatherproof roof.  This can be done in two different ways, either open or closed. Homeowners should discuss the differences in these techniques with a roofing company before a new roof is installed to understand the technology to decide which installation method to use.

What Are Roof Valleys?

A roof valley is a place on the roof where different angles and parts of the roof meet. An example of a valley is where the walls of a dormer meet the main roof, or where the roof over different rooms extends off the main home structure and meets. Valleys are important because they an area where two different roofing surfaces must be seamed together and are also exposed to greater amounts of runoff water than any other part of the roof. All the water from both sides flows into the "V," making valleys an area very prone to leaks if not properly shingled and sealed.

Open vs. Closed Valley Roof Systems

There are two different ways roofers handle roof valleys using different shingling techniques:

  • Closed Valleys - A closed valley is made by putting extra layers of self-adhering, waterproof underlayment beneath the valley where the two roof angles join, then applying shingles as well as sealing and trimming the shingles to form a tight line. The end result is a "V" that water can flow down. The main benefit to closed valleys is to provide a reinforced, direct path for water to flow. They are also considered more aesthetically pleasing to some with no extra trim on the roof. The main disadvantage is that after a period of time, water can get under the edges of the valley and cause a leak if the sealing or trimming is not done properly.
  • Open Valleys - An open valley is a modified closed valley with the addition of a strip of preformed, v-shaped metal that is affixed into the valley to act as a channel for water to flow down. Shingles are trimmed away from the centerline of the valley and the metal channel, made of copper or other weather-resistant metals, is placed in the valley, slightly overlapping the edges of the shingles. The main advantages to open valleys is that the metal channel provides a completely sealed center "V" for water to flow down. Some roofing companies and homeowners prefer the look of this added bit of trim over the plain edges of a closed valley. The main disadvantages of an open valley is that installation is more labor-intensive and it is still possible for leaking if the channel comes off or water gets underneath the edges of the channel.

The choice of open or closed valleys is mainly based on preference, since they both do the same thing with a few minor differences. Closed valley roofs generally cost less, yet may leak after a while if the valleys are not well maintained. Open valley systems cost a little more, but add a measure of protection as long as the channel stays in place. Aesthetically speaking, each method has its fans. To decide whether open or closed valleys are more suitable for a specific roof, homeowners should discuss the options with an experienced roofing company!

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