A properly flashed roof valley should have an ice and water shield installed with roofing felt being properly secured over the ice and water.
How to fix roof valley.
If the ice and water shield is missing then you will have to remove the shingles on both sides along the valley put ice and water shield in place and re shingle the roof.
And if they put a second layer of shingles on they brought it up the valley but they didn t replace the valley it s probably leaking and cracking and split.
Once the roof valley has begun to leak you will need to cover the valley with flashing in order to prevent a repeat of the problem.
It is essential to only use whole not cut shingles during this step.
Clear any debris in the roof valley and surrounding area.
Check the entire roof valley carefully to locate the source of these problems.
As you install roof shingles on the second roof plane you allow them to lap over the valley on top of the first shingles.
And you can tar it but it s a real stop gap band aid like measure.
Start at the upper row of shingles at the upper end of the valley.
Insert the bar under a shingle and pry upward at a.
The right thing to do here is to pull a valley basically pull a valley apart and rebuild it.
The top joinery of both valleys when they meet on the same plane of roof is shown here.
Remove 8 inches of shingles at each side of the valley with a 16 inch nail bar.
Move to the highest end of the valley and work your way down cleaning shingles from both sides of the valley whether they re damaged or not.
In order to lay the flashing the shingles on the roof will have to be removed.
Take measurements of your roof flashing most flashing is 14 inches wide but yours may vary.