Here is a good example of why metal valleys are not the best choice. Fibreglass shingles will resist moisture so you will not see the degree of weathering in the closed valley as observed with an organic shingle. CertainTeed, our shingle manufacturer, prefers that the closed valley method be applied. The shingles look a different colour in each photo because of the lighting. The weather changed suddenly as the valley repair was underway. This is the same valley for all four photos.