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Ice and water shield is a self-adhering waterproofing underlayment that is used in roofing to help prevent damage caused by ice dams and wind driven rain. The following are 3 common uses for ice and water shield in the roofing industry.
1. Eaves and rakes - Ice and water shield is used on eaves to help protect the decking and interior of the home from damage caused by ice dams that may occur due to the freeze/thaw during the winter months. Most ice dams will form down near the gutter and allow water to back up on the shingles which then allows the water underneath the shingles where it can find a nail and make it through deck and into your home. With ice and water shield installed (2' beyond the living area) the water will end up on top of the ice and water shield which seals around the nails and allows the water to run down and into the gutter. Ice and water shield on the rakes performs the same way but instead of water getting underneath the shingles from ice dams it is getting underneath from the water rolling over the edge and getting under the shingles either wind driving it or just gravity.
2. Valleys - It now very common to line the valleys (where two different slopes come together) with ice and water shield. Shingles in a valley on your roof will drape or loop from one slope to the other which makes them susceptible to damage from someone stepping in them, hail or a tree branch falling. During rain valleys on your roof carry a large amount of water and if there is any damage to the shingles in the valley there is then a large amount of water getting underneath the shingles. With ice and water shield installed in the valley, the water will remain on top and make its way to the gutter.
3. Flashings and chimneys - Ice water can also be used under flashings and around chimneys to help protect against wind-driven rains and anywhere the water may be slowed and allowed to back up.