Waterproofing underlayment is installed underneath the shingles in areas where extra protection is needed. High-wear areas like the valleys on the roof, around dormers, rakes, eaves and skylights are good places to put an extra barrier of protection against water leakage caused by ice damming and wind-driven rain. Waterproofing underlayment is self-sealing so that it seals around nails providing a water-tight barrier against moisture.