Ice damming occurs when ice and snow laying on a rooftop melts due to warm inside temperatures. The melted snow flows to the eaves where it freezes again causing an ice dam. Snow continues to melt but the liquid can not drain because it gets caught in back of the ice dam. Water can work its way under the roof covering and infiltrate into the eave areas. Water can also find its way behind the exterior siding which will cause wood rot and mold growth inside the walls. Wood rot damage caused by ice dams can be extensive.
Usually damage is localized at some of the eave areas and can sometimes be viewed during an inspection of the attic space. Ice dams most often occur on lower sloped roofs, or roof surfaces that have multiple transitions from high to lower slopes. Ice damming causes damage to the eaves because it is here that the water refreezes and causes the dam.
Ice damming usually occurs when temperatures are slightly above freezing and when overnight temperatures are below the freezing mark.
One solution for ice dams is to install additional attic insulation and to increase attic ventilation. By increasing ventilation air temperatures in the attic space remain cooler so the snow and ice will not malt as quickly.
When new roofing material is installed, the addition of weather and ice shield along all of the eave areas of the home should help protect the roof sheathing from ice damming conditions.
Heat cables are another method to help keep ice damming at a minimum. The cables are very effective but must be turned on prior to the snow fall to be effective. Heat cables are not designed to be left on all the time because there is an increased risk of overheating and fire. Heat cables must be powered by ground fault circuit interrupter electrical receptacles. It is best too replace the heat cables every two years in order to keep the cables in good condition.
Ice damming can be corrected, the preferred method is to add insulation and increase ventilation. More then one method may be needed to correct the condition in severe ice dam cases.