February 27, 1997

Minimize damage from this year's ice dams and prepare for next winter

With all the snow and cold temperatures of this winter, you may have some unwanted icicle decorations hanging from your roof. If you do, then you probably have ice dams building up, which can cause damage to your house.

A specialist in wood science at the University of Minnesota says a combined short- and long-term approach can help minimize that damage. According to Tim Larson, you can take limited steps to keep existing ice dams at bay this late in the winter. But it is more important for you to prepare for future years by hitting ice dams at their source. "Ice dams can be prevented by controlling the heat loss from the home," says Larson.

An ice dam is a ridge of ice developing at the edge of a roof which prevents melting snow from draining off the roof. The dam grows in size as it is fed by the melting snow above it. The water above will back up behind the ice dam and remain as a liquid. This water will find cracks and openings in the exterior roof covering and flow into the attic space. From the attic it could flow into the home and damage exterior walls, insulation and the ceiling finish. This may lead to the growth of mold and mildew, which could have an adverse impact on the occupants' health.

Ice dams are caused by non-uniform roof surface temperatures. These occur due to heat that comes from the house. The heat can move through the ceiling and insulation, or if there are cracks or openings in the ceiling, the warm air from the house will rise into the attic space and heat the roof as well. "There is a complex interaction between the amount of heat loss from a house, snow cover and outside temperatures that leads to ice dams," says Larson.

How should a homeowner deal with ice dams? Over the long term, you can increase your ceiling or roof insulation to cut down on heat loss. You can also make the ceiling airtight so no warm air can flow from the house into the attic space. However, you should evaluate the impact air tightening will have on ventilation systems, combustion devices and other exhaust systems. Natural roof ventilation can also help maintain uniform roof temperatures. Weatherization contractors are professionals who can deal with the heat transfer problem.

For more immediate action, you can take the following steps:

• Remove snow from the roof. A "roof rake" and push broom can be used to remove snow. However, performing this work on or below the roof can be very dangerous. It's best to have professionals do this job.
  
  
• In an emergency situation to stop water from continuing to flow into the house structure, make channels through the ice dam. Hosing with warm tap water will do this job. Work from the lower edge of the dam up. The channel will become ineffective within days, however, and is only a temporary solution.
  
  
• The ice dam can be removed from the house but places the roof and the remover at tremendous risk. This also should be done by professionals.

For further information on ice dams, refer to the Minnesota Extension Service Distribution Center online catalog for item FS-1068, Ice Dams, at http://www.extension.umn.edu/catalog/item.html?item=1068.

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Source: Tim Larson, (612) 624-6289
Editor: John Winzenburg, EDS, (612) 625-6243, news@extension.umn.edu

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