Ice dams are one of many challenges that homeowners face during the winter months. As the name implies, an ice dam occurs when a thick ridge of ice forms at the edge of the roof, building up along the eaves. This buildup of ice prevents melting snow from draining off the roof as it should. When this occurs, water could leak into the home, causing everything from warped floors, walls and ceilings to soggy attic insulation—the perfect environment for mold and mildew.

How it happens

Ice dams form when heat collects in the attic and warms up portions of the roof, but not the eaves. Snow begins to melt on the warm roof, but then it freezes when it reaches the cold eaves. A dam forms, water backs up behind it, and then it flows under the shingles and into the house. When icicles form along the edges of your roof, it's often the sign of an ice dam problem.

What causes the roof to warm up in certain areas and stay cold in others? The answer is fairly simple: Heat traveling from the house to the roof. This can take place via conduction, which happens when heat travels through solid; convection, or rising air; and radiation, which is the transfer of heat through electromagnetic waves. Let's take a closer look:

• Conduction: Heat moves through the house by conduction through the slanted portion of the ceiling where there may not be adequate space for insulation.
• Convection: Because insulation is warmer along its top surface, the air above that surface rises and transfers the heat by convection to the roof.
• Radiation: The temperature along the top surface of the insulation is higher than the temperature of the roof sheathing, and that transfers heat outward by radiation.

Heat is transferred via leaks in the attic, through exhaust systems in the kitchen or bathroom, and through wood stoves and fireplaces, to name a few.

What you can do

If the problem occurs before you've had a chance to take preventive measures, use a roof rake to carefully remove the snow from your roof. It's important to use a proper rake that won't damage your shingles. If water is leaking into your house, create channels in the ice dam that make it possible for water to drain off the roof. Remember, ice dam prevention begins with controlling the loss of heat from your home and keeping your entire roof the same temperature. Here's how: 

• Increase ventilation in the space between the insulation and the roof sheathing to carry away any heat that leaks through.
• Add insulation to your living space to prevent the conduction and convection of heat through the ceiling.
• Seal any areas where warm air may leak from your living spaces into the attic.