LIMITING ICE DAMS

Ice dams occur when heat escaping through an under-insulated and poorly ventilated attic melts the layer of snow resting on the roof. Water flows down the roof beneath the snow layer and remains insulated by the snow until it reaches the lower areas of the roof where it re-freezes. As the cycle repeats itself, the ice at the eaves builds to form a dam that prevents the water from draining off the roof. Eventually the water backs up under the shingles and can seep through the roof deck and attic into the rooms below.

The result, insulation material becomes soaked and anything susceptible to water damage including wood framing, siding, wallboard, paint and wallpaper is potentially ruined. Ice dams can also lead to mold concerns.

How can ice dams be prevented? At one time, attempting to melt the ice along the eaves using electric heating coils was thought to be the answer for ice dams. However, subsequent studies and long-term experience with the use of heating cables, indicates that maintaining a ‘cold roof’ often is the most effective way to prevent ice dams and the resultant damage.

By improving insulation and ventilation, heat from the house that could contribute to rapid snow melt doesn’t make its way to the attic. Having good air flow from the outside helps move out any heat that does build up, so that the underside of the roof stays cold and the snow melts very slowly and uniformly from the ridge of the roof down to the eaves.

Top - Ice Dam Formation

To reduce the possibility of ice dams forming:

• Clean all leaves and other debris from roof valleys, gutters and downspouts before a snowfall.
• Install additional attic insulation so the thermal resistance or R-value matches that recommended by the local utility or required in new energy codes. Homes built before the 1970s, where the insulation has not been upgraded to appropriate levels or was not properly installed, are prime candidates for the formation of ice dams.
• Consider attic ventilation provisions. If necessary, add more ventilation to keep the underside of the roof deck (sheathing) cool and dry to reduce the rate of snow. Vents may be needed at the lower edges of the roof (eave area) and roof ridge for optimum air circulation.
• If this does not correct your ice dam problems, consult with a reputable roofing and/or insulation contractor about making improvements.