Winter weather with a combination of snow fall and temperatures hovering at and below 32 degrees can create ice dams that cause water to get trapped
on the roof in a quanity significant enough to flow under the shingles and into a living space in the house. A wall of ice actually builds up in the gutter and "dams" the melting water as it travels down the roof. This can happen in temperatures even colder than freezing because the roof is warm and can melt the snow which in turn freezes when it gets to the colder unheated area down by the gutter. Once the water works its way
under the shingles and through the roof
deck it can do a lot of damage to walls, ceilings, and cause mildew, mold, and
fungus issues. The best solution for this
problem is to install Ice and Watershield
up under the shingles and high enough up
the roof to exceed the common area of
ice dam build up, usually 3-6 feet up the
roof from the gutter.