Ice Dams – A Little Known Cause of Damage to Your Home
For a pdf of this article, click here.
Ice dams can occur when as little as 1 or 2 inches of snow accumulates on a roof. Ice dams build up as snow on the upper part of the roof melts, and water runs down the roof under the snow and refreezes into a band of ice at the roof’s edge. Ice dams form along a roof’s lower edge, usually above exterior walls. Heat lost from homes at this point aggravates snow melting and ice-dam development. The increased heat loss is usually caused by insufficient insulation between the top of the wall and underside of the roof. Heat loss also occurs at wire and plumbing penetrations in exterior and interior walls due to lack of proper sealing or insulation.
If the ice dam causes the roof to leak, the insulation can be damaged. And wet insulation doesn’t work well. Over the long term, the insulation compresses. This thinner insulation means less effective insulating qualities and heat lost. As a result, it will cost more to heat and cool your house. Not to mention the potential damage to a homes framing, and the growth of mold and mildew.
Check your home carefully when ice dams form. Investigate even when there doesn’t appear to be a leak. Look at the underside of the roof sheathing and roof trim to make sure they haven’t gotten wet. Make sure the insulation in the attic is dry. If you are unable to verify roof sheathing and insulation integrity, call a roofing professional.
The damage caused by ice dams can be controlled by maintaining the entire roof surface at the outdoor temperature.
For Preexisting homes:
Immediate action: Remove snow from the roof. This eliminates one of the ingredients necessary for the formation of an ice dam. A "roof rake" and push broom can be used to remove snow, but may damage the roofing materials.
Long-term action: First, make the ceiling air tight so no warm, moist air can flow from the house into the attic space. After sealing air leakage paths between the house and attic space, consider increasing the ceiling/roof insulation to cut down on heat loss.
Emergency situation: Where water is flowing into the house structure, making channels through the ice dam allows the water behind the dam to drain off the roof. Hosing with tap water on a warm day will do this job. Work upward from the lower edge of the dam. The channel will become ineffective within days and is only a temporary solution to ice dam damage.
For new construction: Preventing an ice dam is easy. Design the house to include plenty of ceiling insulation, a continuous air barrier separating the living space from the underside of the roof, and an effective roof ventilation system. Insulation greatly reduces the flow of heat from the house to the roof surface, and a good roof-ventilation system helps keep the roof sheathing cold.
