Ice and water shield is a self-adhered, waterproof underlayment installed at roof eaves and valleys for extra protection against ice dam backup and wind-driven rain.
Unlike standard underlayment, ice and water shield fully bonds to the roof deck and seals around fastener penetrations, making it genuinely waterproof rather than just water-resistant. It's installed specifically at high-risk areas — eaves (where ice dams form), valleys (where water volume concentrates), and around penetrations like chimneys and skylights.
Building codes in cold-climate regions typically require it at eaves specifically to prevent ice dam damage; warmer climates may only require it at valleys and penetrations, or as a contractor best-practice rather than a code minimum.
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