ICE DAMS (Causes & Preventions)


ICE DAMS (Causes & Preventions)


The icicles hanging from the roof may look pleasant, but in actuality they are evidence of an issue called ice dams. Ice dams cause water damage to the house. Water stains on walls and ceilings, wet insulation, mold and mildew growth, damaged sheathing and roof structure, warped floors, damaged gutters etc., are the results of ice dams…

How Ice-Dams Form

What Cause Ice-Dams

The snow on the roof melts by hot air inside the attic. This melted snow then runs down, and it freezes again when it reaches the lower part (roof overhang/eaves) of the roof because this part is cold underneath. The formation of ice on the eaves is known as ice dams. This melted snow also turns into icicles near the roof edges.

With time, a big dam of ice forms near the edge of the roof. The melted snow will eventually start to back up. The shingles are designed and laid in a way that they shed (they are not watertight like flat roof membranes) water from the roof, but when the water begins to flow backward/upward, it eventually seep under the shingles and from there, it enters the house and causes damages.

  1. Lower amount of attic insulation: It leads to more heat loss and contributes to higher attic temperature.
  2. Air leakage from the house into the attic space: Air leak can be through attic access hatch if not correctly sealed, the gap between the walls and ceilings, through ceiling lights, whole house fan, chimney penetrations, holes etc.
  3. Inadequate attic ventilation: The best practice is that the air enters from the lower outer part (soffits vents) of the roof and evacuate from the top (maximum or ridge vents). The cold air (from the outside) entering the attic will prevent the hot air (leaking into the house) from melting the snow.
ice dams

How to Prevent the Formation of Ice-Dams

  1. Install underlayment (a watertight membrane that prevents the water that seeped under roofing shingles from entering the house)
  2. Install drip edge flashing (a flashing installed near the roof edge)
  3. Add or increase the attic insulation.
  4. Improve attic ventilation.
  5. Seal any hot air leakage from the house into the attic (this will also reduce your heating costs).
  6. Install heating cables in a zig-zag pattern on the roof edge. Make sure they are ON before the snowfall. (heating cables are not the best solution because they sometimes increase the chances of roof leak)
  7. Some temporary measures are: raking the snow with a snow rake, making a channel to allow an easy path for water.

Written by: Amandeep Singh

Building Inspector
M.Eng. Civil Engineering (Concordia Uni.)
Pictures from: Carson Dunlop


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