The valley of a roof is the area that gets the most impact from rain. The result is that these areas are more high risk for leaks. Ice & water shield rather than just felt should be placed inside the valley to add extra protection.
In a woven valley like this one, each shingle should extend past the center of the valley 8-12 inches and never terminate a shingle in the valley as seen here. Nails should also be placed 8 -12 inches outside of the valley allowing no penetration in the valley itself. This will minimize opportunity roof leaks in your danger zone!
Call if we can help stop your valley leaks!!!