The Colorado Carpenter: Ice Dams on the Darn Roof

Posted by Kevin Stevens | Dec 28, 2011
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Photo: Kevin Stevens of KMS WoodworksA lot of people have heard the expression, "If only these walls could talk." In our homes our walls do tend to talk, but rather than speaking with tongues, they use sign language — some peeling paint here; some staining there. This type of communication is clear to an experienced observer that something is amiss. These observations are not limited to the inside of a home.  Keeping an eye on things outside can also prevent issues from getting out of hand.  Case in point: ice dams.

What's an Ice Dam?

An ice dam is not some pet project of a cold climate beaver, but a phenomenon of heat loss and roof top snow.  In cold areas that receive snowfall, ice dams are common on homes that are not as well insulated or sealed as their non-ice-dam-hosting neighbors.  An ice dam forms as snow melts on a warm roof surface, then flows down to the cooler eave and freezes. Given a level of accumulation, this “dam” can trap even more water which can then leak under shingles, penetrate roof sheathing and cause a number of water related issues.

Causes of Ice Dams

The root cause of ice dam formation is heat loss into the attic space that then flows through the roof decking and melts the snow above.  This heat loss can be due to a number of issues. The two top contributors are insufficient insulation and air leaks.  Depending on your location, recommended attic insulation amounts vary from R-30 to R-60. For those not familiar with these levels, R-30 roughly equates to about 9 ½” of fiberglass.  If your home has the proper thickness of insulation but you are still getting ice dams then you may has excessive air leakage.  Common air leaks occur around pipe penetrations and other fixtures that may enter the attic space. Poor or non-existent attic ventilation can also contribute to ice dam formation.

Treatment and Prevention

Like a medical condition, treatment is possible to render the symptoms of ice dams less damaging.  The symptoms here are the dams themselves, which can be treated with electric heating elements, which prevent the snow-melt from re-freezing, or by mechanical means like chipping, shoveling, etc.  Another treatment is to reduce the ill effects of ice dams (namely the water intrusion and damage they cause) by applying an "ice and water shield" membrane below the roof’s shingles along the eaves.  In many cold climes the installation of this protective membrane is a code requirement.

Both of these mechanisms treat the symptoms of ice dams — not the cause.  As is common in most scenarios, prevention is the better route to treatment. To prevent ice dams from forming, a well insulated and sealed attic space will prevent the snow from melting from lost heat in the first place. Added ventilation can help, but if not combined with insulation and sealing it can add to heating costs.  When thicker levels of insulation are used it is important to provide an air break from the eave to a point above the level of insulation. This is easily done with special baffle panels designed for this simple task. The use of these baffles allows for a uniformly "cool" roof deck.  Visual inspection of snow loads can show how effective your prevention plan is working.  An easy way to see if the snow on your roof is melting is to compare the heated space with a non-heated space, like a garage.  If the levels of snow are about the same, then you’re on your way to an ice dam free home.

Kevin Stevens is a Networx - - writer. Get home & garden ideas like this - - on Networx.

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