The California Weave is a closed valley system that gives a second layer of protection to the largest drainage areas of your roof. Guyette roofing puts metal in every valley, no exception. Next, a base layer of shingles are installed directly on the metal. Nails are only placed on the extreme edges of the metal. After the base layer, a second layer of shingles coming up the other slope are installed. Last, the second layer is cut down the middle of the valley to provide a symmetrical, easy to drain surface.