In climates of moderate to heavy snowfall, ice dams can cause a roof to leak along the eaves. An ice dam forms when snow melts over the heated portion of the house and runs down the roof, freezing at the cold eaves area. Ice builds up along the eaves, trapping drainage in pools that eventually flood under the shingles into the attic.

New roofs on homes in such climates generally receive a special membrane beneath shingles along eaves to prevent water penetration. Proper ventilation does an excellent job of minimizing the thaw/freeze cycle. By building a ventilated, cold roof, cold air can circulate from eaves vents to a continuous ridge vent, neutralizing temperature variations on the roof. Roof insulation helps keep heat in the rooms during winter and blocks heat gain in the summer.

If you can't easily retrofit proper ventilation, you can install electric heating cables along the section of roof above the overhangs.