The valleys in roofs are highly susceptible to leaks due to the amount of water being concentrated into them. For this reason, properly installing the shingles at valleys is crucial to maintaining the water tightness of the roof. There are several ways to shingle a valley, but in this article I am going to focus on just the closed-cut valley version and the problems that can result when it is not installed appropriately.  

Below is a diagram of the proper steps to installing shingles as a closed-cut valley:

My Job:

My job during the home inspection is to look for abnormal and harmful water penetration into the home. To best locate these concerns I need to know what kinds of construction techniques and designs are susceptible to water penetration if installed poorly or incorrectly. The closed-cut valley installation is one of those techniques that I often find installed improperly, which at times results in water penetration at the valleys.  Below are two of the most common mistakes and the results of those mistakes:

The cut was made in the center of the valley instead of two inches off the valley. 

The cut was made up on the smaller and less steep roof instead of being cut back on the steeper and larger roof. 

Conclusion: 

As you can see, making mistakes with installing shingles at roof valleys are sure ways to invite water penetration into the home. If you have concerns about your roof, let me serve you by providing you a visual inspection of your roof. This would include looking at the roof flashing and inspecting the roof structure from the attic access. When you really want to know, contact Adam Duncan of Duncan Home Inspection Services, LLC.