What is ice and water shield, and what does it do?
Why it exists
Shingles shed water well as long as it runs downhill. Trouble starts when water backs up or moves sideways: behind ice dams in cold climates, under shingles in wind-driven rain, or in valleys where two slopes pour into one channel. Regular underlayment is a backup, but water can follow nail holes through it. A bonded, self-sealing membrane closes that gap.
Why Georgia roofs use it without much ice
- Valleys collect water and debris like pine straw and leaves, which slows drainage.
- Chimneys, skylights and walls are where flashing leaks begin.
- Pipes and vents get a backup layer under the pipe boot.
- Low-slope sections drain slowly in summer downpours.
- The North Georgia mountains do see ice dams in some winters.
How it differs from underlayment
Underlayment, felt or synthetic, is nailed down and is water-resistant. Ice and water shield is fully adhered and waterproof, and it closes around nail shanks instead of letting water follow them. It also costs more, so most roofs use it only in the high-risk spots, with underlayment elsewhere. The comparison is in synthetic underlayment vs felt.
Where the name comes from
Ice & Water Shield began as one manufacturer's product name, and it became the everyday term for the whole category. Manufacturers also call these products leak barriers or self-adhered underlayments, tested to ASTM D1970. Where it sits in the roof is shown in roof anatomy explained, and Georgia placement is covered in ice and water shield in Georgia.