1.1 This specification covers polymer modified bituminous sheet materials intended for use as underlayment on roof eaves, or valleys, or both, to prevent leakage of shingle, tile, or metal roofs from water back-up due to ice dams. This specification covers the standards for polymer modified bituminous sheet materials proposed for use as underlayment on roof eaves, or valleys, or both, to prevent leakage of shingle, tile or metal roofs from water back-up due to ice dams. The und