A client changed their roof cover based mostly on a long term leak on an asymmetrical roof valley (bottom half is 12/12 on one side, 4/12 on the other. Top half is 12/12 on both sides). I specified a prefabbed copper flashing at the junction between the upper and lower halves because that point has three dimensions (flat flashing can't be bent to fit).
Two months later, it's leaking again. Is anyone aware of any guidelines for flashing an asymmetrical valley?
Thanks.