Preventing heat loss into the attic and removing snow from the roof are two ways to prevent ice dams. Keep the attic cool by sealing gaps, adding insulation and improving attic ventilation.
Ice dams form when the roof heats up due to warm air in the attic. This melts the snow on the roof. When the melted snow reaches the cold edge of the roof along the eaves, it refreezes and turns to ice. The dam continues to grow as the ice builds up. Water can leak inside the roof and along the walls.
Minimize the transfer of warm air from the home to the attic to prevent the heating and freezing cycle. Sealing around recessed lights, chimneys, ducts and gaps in walls prevents the heat from entering the attic. A layer of insulation can also keep the attic cool in the winter.
Ventilation in the attic draws warm air outside and brings in cold outside air to keep the attic cool. Adding vents and keeping them unblocked helps improve ventilation.
Because snow is the cause of the ice dam, removing it from the roof is a temporary way to prevent a problem. Home improvement stores sell roof rakes designed to pull the snow off the roof. Use the rake with caution to avoid damaging the roofing material. Never climb on a snowy or icy roof to remove snow.