Ice dams develop when snow is on the roof, outdoor temperatures are only slightly below freezing, and there is spot or generalized heat loss from the house into the attic/roof section of your house that accumulates under the roof deck. The heat melts the bottom of the snow pack, the melted snow runs down the roof until it gets to the overhang of the roof. Without the heat from the house, the water freezes, creating an ice dam.
What is ice and water shield?
The most common approach in preventing ice dams is a precaution from keeping the ice dam from getting inside once it has formed. This is an ice shield membrane sometimes called Ice & Water shield. Ice and water shield is a self-adhering rubber roof underlay that seals to the roof deck and should be applied a minimum of three feet up from the roof edge. Ice and water shield should also be applied under valleys, around chimneys, skylights and other problem areas. There are many ice shield membranes available on the market, what they do is seal down to the wood roof substrate (plywood or nominal lumber) and also seal around any nails. This ice shield should extend from your gutter line, at least 24″ past the exterior wall.
Why we use ice and water shield?
Ice and water shield is the premium protection against ice and water problems. In weather conditions such as heavy snow and ice this membrane will provide maximum protection for your roof which in turn is protecting your home and all the valuables inside.