What is an ice dam, and how does it form?
When snow accumulates on a roof, a cycle of melting and refreezing occurs. In a perfect world, the snow would melt off the roof, enter the gutters, and flow harmlessly to the ground. Or the snow would evaporate from the action of the sun, and never really melt off unless the outside temperature rose above the freezing point. However, two key factors interact to cause problems… the outside temperature and the temperature of the inside of your attic.
The warmer your attic is, the more melt off that occurs at the roof surface. This melted snow would normally flow off the edge of the roof. Under certain conditions, though, when air temperature is very low, the water refreezes at the edge of the roof, where the interior roof surface is not being warmed by the attic. This refreezing gradually forms what is fondly known as an “ice dam”, a growing heap of ice that blocks path of the melted snow.
Once this dam forms to a certain height, the melted snow that pools up behind it can suddenly leak back under the roof shingles and into your home! On a roof with a low slope, it only takes a small ice dam to cause water backup and leakage.
Contrary to popular opinion, gutters do not cause ice dams. However, an ice dam can extend into a gutter if weather conditions permit.
How can ice dams be prevented in the first place? The answer… insulation and ventilation!
Since we have determined the main cause of ice dams to be an overly warm attic, a good start in inoculating your home against ice dams is to reduce the attic temperature by installing additional insulation on the attic floor. Install weather stripping and/or insulation on attic stairways or hatchways, and on attic floor-mounted louvers for whole house ventilation fans. Be careful if there are any exposed recessed light fixtures or vent fans poking through the attic floor. Some of these are not designed to be covered with insulation.
For more information, please feel free to call MI Construction & Roofing at 630-241-0001.
Jack L. Mancione, CEO