An ice dam is a large block of ice that forms on the lower edge of your roof. This ice is formed with the upper snow melting and freezing to the bottom of your roof. As it grows a reservoir is formed and water is held and pushed back into your single then home. The permanent solution to this would actually be insulation in the attic. When there isn't the correct amount of insulation during the winter when you are running your heat in the house, some of the heat escapes to the attic. The attic then warms the roof and melts that snow on your roof.