An ice dam is a ridge of ice that forms on the roof as a result of a freeze-thaw cycle. When heat escaping from the attic starts melting the snow on the roof, the water flows under the snow and re-freezes when it reaches an unheated portion of the surface – usually at the eaves. As changing temperatures cause freeze and thaw cycles, the ice dam grows and gets thicker and it starts to spill over the eaves and cause icicles. In the meantime, water is prevented from flowing down the roof and will eventually back up finding its way under the shingles and into the attic and living space of the home causing damage to walls, ceilings and insulation. A thick ice dam can damage roof flashing, fascia and soffits and can even shift vent stacks and create gaps that allow for even more water to seep in through the roof.