Ice Dam Formation

Ice Dam Formations are an all too prevalent in many Northern climates throughout the United States. As soon as your roof has snow and ice accumulation for extended period of time, your home could be susceptible to this issue. Many factors can contribute to this issue, but attic ventilation is generally the best place to start in addressing this concern.


How does an ice dam form?


  • Snow accumulates on the roof.
  • The roof warms up from heat loss within the house and from solar heat generated. 
  • This warming is just enough to partially melt snow turning it to water. The water then runs down the roof line underneath the snow until it gets to the roof edge.
  • At the roof edge, the surface temperature is lower again causing the water to refreezes into ice. (This is sometimes visible in the form of icicles hanging down.)
  • Over time, the snow can continue to melt higher on the roof, drip down as water and refreeze as ice at the roof edge. As more water comes down, it can build up the ice and act like a dam keeping the water from running off properly. 
  • As additional water comes down, it can be trapped behind the dam of ice. It can back up under the shingles and leak into the warmer attic and melt into water. Leaks can then occur in any number of places in the house. 

How can this risk of ice dam be mitigated?

  • The attic temperature should remain as close to outside ambient temperature as possible. If the attic remains colder, you reduce the cycle of melting, freezing, and melting snow.
  • It may seem counterintuitive but under these conditions, you want your attic to be as cold and drafty as possible.
  • The attic should be well insulated away from the living areas with warm air leaks to the attic minimized.
  • The attic should be well ventilated with outside air. The cold air needs to be brought into the attic to keep roof and eaves at outside temperatures.

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