Ice dams are created when an existing snow blanket begins to melt and water runs downward. The water pools against frozen snow mounds below and refreezes, building an ice dam. Later, more melting snow causes water to pool at the dam. Destructive forces go to work. The roof can leak. The weight of the dam, its melting, refreezing, expanding and contracting can put pressure on gutters and other trim.
Since lost heat is a huge contributor to the formation of ice dams, checking the attic and roof before winter is the beginning of defense. Water seepage from previous winters may have damaged insulation. Additional insulation may be needed. Before snow falls, placing heat tape in a zigzag pattern on the roof is another help toward preventing the buildup of ice dams. You can use the heat tape as soon as snow season begins to help melt ice before it accumulates at an excessive depth.
Those holiday cards adorned with icicle-draped country cottages look nostalgic and cozy, but the truth about icicles is not charming. Icicles form where heat is lost from the house, so each monster icicle represents the expense of lost heat. Additionally, heavy icicles can break and fall. Commercial heat tape can create a drainage path for melting snow and ice. Where icicles would have formed, ice melts and drips away.
In the best of cold climate building and renovating situations, vents would pass through a minimum of unheated space. Ample insulation would surround all vents. In cold climate reality, ice can accumulate around vent stacks. Additionally, plumbing vents can produce vapor which can in turn condense and freeze. Wrapping commercial heat tape around accessible vent pipes helps to keep them open and doing their job, providing ventilation.