Now that we have finally had our first appreciable snowfall in the Rochester MN area we have to be on the lookout for Ice Dams. Ice dams are the result of snow melting on the roof due to poor insulation. Ice dams, which are a ridge of ice along the eaves are the result of the interaction among the homes heat loss, the amount of snow cover, and outside temperatures. In order for an ice dam to form, the upper portion of the roof must be above freezing, and the lower portion near the eaves below freezing over a period of time. Melting snow from above travels down to the eave and re freezes, over time this builds up and results in the ice dam. As water builds up behind the dam, it will eventually find cracks or openings under the roofing covering and flows into the attic space, into the insulation and possible the walls.
Ice Dam / Roof Cross Section
To help eliminate, reduce ice dams, you should resolve any insulation issues. Secondly, use a snow rake to pull snow from the eaves. Another method is to install the wire heat tapes. These devices are typically strung in a zig zag fashion along the edge of the roof, up past the cooler portion of the roof. The heat tapes will keep an open path in the ice or snow that will allow water to escape.