Having served southern New Hampshire communities for many years, we have investigated and resolved hundreds of ice dam problems. Although each case was somewhat unique, they always have two things in common. They happen because melting snow pools behind dams of ice at the roof’s edge and leaks into the house, causing thousands in damages to home owners. Ice dams and the damage that results from them is avoidable.
What Causes Ice Dams?
Ice dams form when melted snow refreezes at roof edges. Three things are required for an ice dam to form: snow, heat to melt the snow and cold to refreeze the melted snow into solid ice. Ice dams can form when as little as 1 or 2 inches of snow accumulates on a roof – if the roof is poorly insulated and air sealed, and the snowfall is followed by several days of sub-freezing temperatures. Ice dams develop as snow on the upper part of the roof melts. Water runs down the roof slope under the blanket of snow and refreezes into a band of ice at the roof’s edge creating a “dam”. Additional snow-melt pools against the dam and eventually leaks into the building through the roof or roof trim.
The reason ice-dams form along the roof’s lower edge is because the upper roof surface is at a temperature that is above freezing while the lower part of the roof surface is below freezing. The upper roof surface is usually located directly above the living space. Heat lost from the house warms this section of the roof, melting snow in this area. During periods of sub-freezing temperature the lower regions of the roof deck remain at sub-freezing ambient temperatures. Roof overhangs are not warmed by indoor heat-loss. The trick is to keep the entire roof below freezing if possible. Roof ventilation helps achieve this.
How To Resolve Ice Dams
The damage caused by ice dams can be controlled in 2 ways: Maintain the entire roof surface at ambient outdoor temperatures or build a roof so that it can’t leak into sensitive building materials if an ice dam forms. If your home experiences ice dams in the winter, please contact us to inspect your home. Diamond Hill Builders will properly diagnose the cause of your ice damns and assure you have proper insulation and ventilation.