ice dam

How to Help Homeowners Understand Ice Damming

Print Friendly, PDF & Email

The cold winter season is the time when many homeowners see icicles hanging from their eaves and/or water coming in the house due to ice damming on the roof.

There are three main causes of ice damming:

  • Poor insulation from a house ceiling. An attic with inadequate or deteriorated insulation can cause ice damming.
  • Lack of ventilation. A house with proper ventilation allows the necessary cold air to mix and cool the hot air from the house, which slows the snow melting down.
  • Leaking gaps between the living space and the attic. These spaces allow extra heat to “escape” into the attic, which warms the space and melts even more snow.

Snow on the roof will eventually melt, but if the heat from the house causes the snow closer to the roof to turn into water, then that water can either go down slowly to the gutter or travel under the shingles. There is no heat at the gutter, so snow will remain there, creating a barrier. The water that is moving down will hit that cold snow barrier and then freeze again. This creates a dam (ice damming), which will hold the remaining water on the roof.

Shingle roofs are designed to shed water; they cannot handle having it freestanding. That is why a good quality leak barrier is needed at the eaves. To help your homeowner understand the importance, you can perform a simple test with a bottle of water. This will show that every nail going through the leak barrier is automatically sealed.

The most important thing a contractor can do to help homeowners with ice dam problems is to first clean the snow off the roof (following strict safety rules) and then create exits for the trapped water.

In the long term, the contractor should:

  • Seal the living space.
  • Install adequate attic insulation.
  • Make sure that the attic is properly ventilated.

Preventing ice dams and icicles may not be possible at all times, but these are measures that can be taken to help stop water from entering the house.

There are 6 comments

Add yours
  1. Dave Bolender

    I agree – great article
    However, there is a 4th factor that contributes to ice damming, which has nothing to do with attic air-sealing, ventilation and insulation. It is “solar heat gain” from the sun itself. My Toronto, Ontario neighbour asked me (this week) about large icicles hanging from his garage eaves along with the ice dam above the icicles, while his upper house eaves were fine. As the garage is unheated, he could not understand it?

    I explained to him that it was all to do with the exposure of his lower garage eaves and the way the sun tracks across his house and property, plus the fact that this section of eaves becomes shaded very quickly, after bright sun exposure – even on a freezing cold winter day. In fact I have confirmed up to a 25 degree (celsius) temperature swing several times, when air temperature is -10C, but the roof or surface temperature is +15C in bright sunlight. This is the reason for this ice damming. It is also why snow will melt on an asphalt driveway when air temperatures are freezing. Yesterday – here – was very cold at -12C, but two ice patches on my driveway were melting and running water in the clear, sunny day.

  2. John McLellan

    Very important information Paulo.
    Ventilation, insulation and air sealing are three very important factors,but the fourth cause of ice damming is not often discussed: inconsistent shadowing on the roof caused by dormers, walls & sometimes trees. Take a snowy roof at -5°C (22°F) on a sunny day; The sun melts the snow and the water runs into shadowed areas on the roof where it re-freezes causing intermediate ice damming. This can also cause ice dams and leaking on unheated garages, sheds and outbuildings. As you mentioned, not all ice damming can be prevented, but knowing this Fourth Cause makes it easier to sell Leak Barrier and full deck production on these unheated portions of roofs.

  3. Rock and Tait Exteriors LLC

    Great article- I shared it to our Facebook pages! As a GAF Master Elite company we specialize in proper ventilation techniques. Plus we are insulation specialists too so we can help with preventing ice dams as much as possible that way.
    If you are in the Western/Central Wisconsin area (Hudson-Eau Claire-Wausau) call Rock and Tait Exteriors to start with a free estimate! 1-800-519-9894

Post a new comment