Ice dams are the build up of ice, generally along the roofs edge.They are the result of snow melting on the roof and freezing before it has the chance to run off. With a number of such cycles, the dam of ice builds up as more and more water freezes and pools behind the dam. As the ice dam spreads up the roof, water can eventually work its way under the shingles and enter the attic. Once the water enters the attic, it can damage the roof, ceilings, walls and contents of your home. If the attic insulation becomes wet, the value of the insulation is lost and can lead to a rise in temperature of the attic which can accelerate the growth of the ice dams. Look for the formation of icicles, which is a sure sign of ice damming.