If a metal flashing has been used the most common problem is that the shingles were improperly cut.
Roof valley leak.
Sometimes an older home s roof is more prone to leaking in the roof valleys because of old repairs.
The roofing nails are fine so long as the lead of the roof valley is intact but once it starts to crack or fracture due to water pressure corrosion or other damage the nail provides a space for water to run into the home.
If your roof valley leak is an old repair gone bad consider having a professional repair the leak properly.
A flashing is a transitional roofing material that connects the roof material to some other building material or to another part of the roof.
This method is a similar method to what mike guertin calls a long island valley which runs shingles from the first slope past the valley and up the second slope.
The edges are finished in a similar fashion to garcia s method.
Valley roofing did an excellent job when they installed a new roof in my home back in august of 2019.
Fast forward to october of 2019 we start to have a rodent problem in our home.
Roof cement should be dabbed under the shingle corners.
Roof leaks in a valley can be prevented.
Start low soaking the area just above where the leak appears in the house.
And damaged flashing is behind most roof leaks.
Many roof valley leaks are caused by roofing nails that have been poorly placed and are acting as a dripper feeding water through from the roof above.
Isolate areas when you run the hose.
Most shingle installers will use a thick 30 lb paper as a base for the valley.
The sealants and roof pitch used can crack and chip away over time.
Most roofers that do shingles will use a heavy base paper instead of a rubber membrane.
In either situation the leaking roof valley can be fixed by removing affected shingles and structural elements and upgrading your roof s flashing.
Shingles are then bedded in cement going up the valley.