Ice and water shield is made of polyethylene and rubberized asphalt; this membrane prevents water that has slipped under shingles from penetrating to ceilings below. A quality roofing company will know the codes for the city that you reside in. We install synthetic felt paper on every new/reroof we install. The valleys should then be covered with metal flashing or weaving. Again, a quality roofing company will know what your city requires for code and how to install the materials to protect your investment in your new roof and home.