Increasing ventilation, adding insulation and sealing air leaks that warm the underside of the roof are effective ways to prevent ice dams. Preventing the underside of a roof from becoming warmer than the eaves and keeping the roof cold stop ice dams from forming.
Ice dams form when snow and ice that have accumulated on a slanted roof begin to melt from heat escaping to the underside of the roof. Because the air temperature keeps the eaves cold, the water running down the roof freezes when it reaches the eave and accumulates to form a dam or wall of ice that prevents water from draining and running off. The remaining meltwater accumulates to form a reservoir that saturates the roof sheeting, soaks through the roofing material and leaks inside the building.
Preventing an ice dam requires maintaining the underside of the roof and eaves at the same temperature. Adding insulation to the attic floor to prevent warm air from rising to the roof’s underside can be an effective method of keeping the roof cold. Sealing any leaks that allow the warm air to escape into the attic is also effective. Properly venting all heat-causing appliances such as heaters, electric dryers, stoves and fireplaces can help minimize the build up of warm air in an attic. Some buildings may require installing a ventilation system that draws cold air inside the attic and forces warm air out.