An ice dam is a condition which develops along a cold eve where snow on a roof melts over the warmer living area then runs down and refreezes at the gutter or eve. Water then backs up under shingles and leaks into the living area. Most new home warrantees exclude this condition but try explaining to a new home buyer who just spent hundreds of thousands of dollars on a new home that the water leaking into their living room is not covered.
There are a number of steps that can be taken to reduce the number of incidents if not prevent them all together. Cold well ventilated attics are less prone to ice dams because the roof is not as warm a vaulted ceiling area or an area that is not properly vented. Try to avoid vaulting roofs all the way to the underside of the rafters and provide good ventilations.
We installed a membrane such as Grace's Ice and Water shield above the eves. The membranes prevented backed up water from entering the living space. This simple detail virtually eliminated the problem. It worked so well that we added the membrane to other problem areas such as roof valleys and where dormers me roofs. We also used it on roofs with shallow roof pitches.
If the membrane is not installed during construction there are a couple things you can do. First us a roof rake to remove the snow before it builds up. This can be problematic in heavy snow of overnight snow fall. The only prevention is installing a heating cable in the gutters, downspouts and in diagonal patterns above the eve. These cables will form paths for water to run off. This method works reasonably well as long as you remember to turn on the cables. Your new homeowner will likely not appreciate the cable on the roof.
Original Content copyright 2011 Thomas Robinson
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