Roof Valley, open valley, closed valley
A roof valley is created when any two sections of the roof meet at an angle that is less than 180 degrees, it creates a valley.

This blog about roof valleys is part of a 6 part series on roofing underlayment. To access the main page of this series and learn more go to Roofing Underlayment 101: An Overview Of Roofing Underlayment.

A roof ‘valley’ on your roof is created when any two sections of the roof meet at an angle that is less than 180 degrees. Because water is most likely to collect and accumulate at a valley, it is one of the more to vulnerable parts of the roof. In this article, we’ll be discussing what a roof valley system is, its importance and the 2 typical styles.

A roof valley system is applied in areas of the roof that tie in to each other at an exterior angle of fewer than 180 degrees. For a proper valley system, ice and water should be installed underneath a metal flashing that is installed underneath the shingles. From there synthetic underlayment, starters and shingles are applied over the metal to waterproof the area.

A roof valley is necessary for mitigating the risk of damage being done to the roof from prolonged exposure to moisture. It helps fight off mold or algae infestation from occurring by keeping the valley areas well protected.

Types of Roof Valleys

Two of the most common ways of sealing the area are the open valley and closed valley methods. In this section, we introduce you to both types and highlight their differences.   

Closed Valley 

To cover and seal the valley, a layer of underlayment and an ice and water shield is installed over it. Afterward, the shingles are installed, starting with the lower slope and, later, on the higher slope so that they effectively overlap each other. The excess part of the shingles on the higher slope are cut off so that the overlap appears seamless. 


  • More aesthetically pleasing 
  • Quicker to Install
  • Often Cheaper


  • Higher Chances of Failing 
  • Shorter lifespan 

Open Valley 

In an open valley setup, the ice and water shield and the underlayment are installed under the shingles in the same way as in a closed valley. However, instead of overlapping shingles, a pre-bent metal flashing is installed over the valley area. This effectively seals off the vulnerable middle area of the valley and allows you to install the shingles 3-4 inches out from the middle.

By having the middle of the valley remain open thanks to the metal you effectively accomplish a couple of things.

First, because valleys collect water flow from 2 sections of roof they are inherently high water flow areas. Over time the exposed metal can handle the corrosive effects of the water much better than shingles. We often find that valleys are the first places to deteriorate in the event that a closed valley system has been installed.

Secondly, by having the ability to keep the shingles away from the valley this reduces the temptation to want to nail too close to the valley. Open valley’s are perfect for creating a nice clean basin to collect and direct water flow down the roof. Open valleys guarantee that no nail perforations will be anywhere near the area that collects the most volume of water.

While we can install any type, open valleys are definitely most recommended to maximize the longevity of your roof!


  • Lower chances of failing 
  • Longer lifespan 


  • Slightly higher cost 
  • Less aesthetically pleasing 

Concluding Note 

Regardless of which method you choose for your roof valleys, the final result is only as good as the roofers you hired for the job. It is always recommended to work with professional roofers who have the qualifications and training needed to properly implement the task. If you are a resident of Hamilton and in need of expert roofing service, feel free to get in touch with us by calling 905-746-5792 or emailing us at  

Published On: April 27th, 2020 / Categories: News / Tags: , , , , , /

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