Ice and Water Shield: What Is It? Do I Need It?
Ice and water protector, sometimes also referred to as ice and water shield, is a waterproof roof underlayment membrane developed to protect vulnerable areas on a roof from ice and water damage. Ice and water protectors (sometimes called ice and snow shields in cold climates) are made with a rubberized asphalt membrane that goes beneath the shingles of your roof.
Ice and water shield looks like a long sheet of sticky black plastic. It's available in several different brands, including Grace, WeatherLock, Weather Watch, Moisture Guard Plus, and more.
The adhesive back surface of the membrane will bond to the roof deck, which is a superior underlayment for areas where ice dams or severe storms are common. Ice and Water Shield underlayment should be used in conjunction with roof designs that minimize ice dam formation. In cold climates, it is particularly important to provide proper insulation and ventilation to reduce the size of ice dams and to avoid interior condensation. Cathedral ceilings must include ventilation between rafters to allow for air flow to a ridge vent. Well ventilated cold roof designs are particularly important in alpine regions to reduce the size of ice dams which could contribute to structural damage. Several variables will influence the height of ice dams and the membrane coverage required.
Ice and water protector products have a modified bitumen adhesive back surface that is covered by a release film. The film is removed during application so that the membrane will adhere to the roof deck and also form watertight end laps and side laps when properly applied. The modified bitumen is designed to form a watertight seal around the nail penetrations when shingles are applied.
A safety feature of these membranes is a slip-resistant top surface for better traction during installation. Potentially, covering an entire roof with ice and water protector can prevent leaks even after high wind conditions blow shingles off the roof—preventing further damage and making repair easier. However, because the modified bitumen back surface is continuous, these membranes can result in a vapor barrier. Should a homeowner decide to cover the entire roof with ice and water protector, it is even more important to consider proper attic ventilation carefully.
The only real negatives of covering your entire roof with ice & water shield are (1) cost and (2) potential ventilation problems (which are very rare). Ice & water shield acts as a vapor suppressor, so it not only keeps the water out, but also keeps the moisture in.
The good news is that this shouldn’t be a concern if you’ve got a well-ventilated attic. If you don’t have a well-ventilated attic, then that’s just one more reason you are (or will be) dealing with ice dams. If you’re one of the extra-diligent homeowners who requests that your entire roof be covered in ice & water shield, make sure to ask your roofer whether you’ve got adequate ventilation in your attic.
Roof Wolf prefers to cover your entire roof with ice and water shield to offer the most protection possible.