Its that time of year again when the snow flies and with it comes ice dams. As the snow pack begins to build up on roofs it begins to act as an insulator. Improporly vented or insulated house will being to melt the snow from the bottom. As the melted snow runs down the roof it will inevitably run into cold air be it from the over hang or out from underneath snow. As the dam begins to build up, eventually the melted snow can know longer flow off the roof and begins to travel back up the roof.
Some people think that taking a snow rake to the edge of the roof is the solution. There are two significant problems with this theory. The first is that raking the snow off the roof also removes some of the granules from the shingles which shortens the life of roof. The second is that in conditions of extreme cold, only removing the lower couple of feet of snow can back the ice dam farther up the roof.
Solutions to ice dams include: proper ventilation with a soffit and ridge vent, installing a new roof with a minimum of six feet of ice and water barrier, proper attic ventilation, and the best is all of the above.