What is a dead roof valley?
A dead valley is generally used to describe an area where a valley meets an obstruction such as a wall or chimney. The lowest portion of the valley is generally of a lower slope as well. The trouble in this design is that rain water must make a hard and abrupt turn. In addition, water is also more prone to splashing against the vertical surface.
Here is a good photo of a dead valley:
Mixed Valley Intersections
Another common reference to “dead valley” is at mixed valley intersections. Here you can see that three separate roof angles collide together. They are joined at the bottom by a lower sloped “triangle”. This is fairly common on hip type of roofs.
Shingles are designed for water to flow in a downward direction only. Pictured above you can see water may flow down the steeper slopes. Once it hits the dead valley area it may then run laterally across the lower pitched “triangle”. This would be exaggerated even more during severe rains. Understand that each shingle is about 3 feet long. Each shingle also covers the previous shingles nails. If water constantly hits a shingles edge it does not take long to find and rust through a nail. Mixed valleys or dead valleys are one of the most overlooked areas of a hip designed home.
The Solution -Rolled Roofing
The solution is to first identify a dead valley and build a game plan to ensure future leaks do not occur. Our most common solution is to install a product such as rolled roofing (modified) which is made for lower pitched slopes. The solution is that these rolled goods are made for slow drainage areas. There are no side laps every three feet like shingles so it does not matter if water flows laterally across it. Most importantly there are no nails for water to find as it is self-adhered!
Here are some of our previously completed dead valley solutions: