Any roofing system has to have protection from water-related issues. This includes wind-driven rain, flowing water, ice dams, seepage and other water problems. A roofing underlayment system can be used to alleviate water concerns. The best product to use for these water concerns is an ice and water shield product.
Used under standard type roofing and conventional asphalt shingle, ice and water shield will effectively resist water penetration. Areas around vents, chimneys, skylights and valleys are also protected from water intrusion. Anywhere water tends to collect and flow can be kept safe from damage by using an ice and water shield product.
All the products function in the same general way. They keep water from seeping under your roof and doing damage to your roof, attic and even the interior of your home.