Blog – Expert Roofing Advice & Tips

How To Prevent Ice Damming

how to prevent ice damming

You might not have heard of ice dams before but it is very likely that you have seen them in the past without even realizing it. One of the most visible signs of ice damming on a roof is icicles hanging off of the eavestrough. 

Ice dams can cause significant damage to your eavestroughs, roof shingles, roof sheathing and even water damage inside your home. So doing everything you can to prevent ice damming is crucial.

While there are a number of ways to help stop ice dams from forming each year, including using a roof rake to remove snow as soon as possible, you can minimize their effects if you take steps to stop ice dams in the long term.   

2 Steps to Prevent Ice Damming

Ice dams form and can be prevented, based on the air temperature in your attic space. When your attic is too warm, due to heated air leaking in from the living spaces below, it melts snow on the roof.

The water runs off the roof until it gets to the roof overhang, which is colder. The water then freezes and starts to block more water from getting into your eavestroughs and draining away. It’s that water back up that can seriously damage your roof’s surface and other parts of your home.

You must do the following to keep your attic cold enough to prevent ice dams, while not compromising the comfort of your home.


  1. Keep Warm Air Out of the Attic – Again, your attic warms up due to warm air leakage from below. In addition to causing ice dams, the leakage is an indication that your attic insulation levels are too low. You should have at least 16-18 inches of batt or blown cellulose attic insulation in a Toronto or GTA home. For fibreglass insulation, it should be at least 22 inches. It should also be dry. If you’ve had ice dams before, your insulation may have become damp and the moisture reduces its insulating capacity.
  2. Allow More Cool Air Into the Attic – Cold air gets into your attic through your roof’s attic ventilation system. If the system is too large, too small or not properly configured, it can let in too much or too little outside air. In the case of too little cold air, your roof may heat up enough to cause ice dams even if you have sufficient insulation. The key to an effective roof ventilation system is to make sure you have vents located low in your roofing system, like soffit vents on the underside of the roof overhang, where air can get in; and other vents, like ridge vents, at or near the peak of your roof, where the warmer air can escape.


Unfortunately, in some situations, the design of your roof can also increase the likelihood of developing ice dams. Although the insulation and ventilation system should be evaluated, if those components of the roof are in good working order then other steps might be necessary. 


This can be the case if you have dormers on the roof that are close together or multiple valleys coming together as both of these scenarios confine the flow of water and snowmelt to one concentrated area. If this is the case, the installation of heating cables may be necessary to keep ice from backing up.

If you enjoyed this post, check out our recent article about all the benefits of maintaining eavestroughs all around your home.

Please note: Chouinard Bros. does not recommend any homeowner complete repairs to their roof of their own. Our technicians are skilled at performing this work and have received years of training to understand how to complete repairs safely.

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