how do ice dams damage roofs

How do Ice Dams Damage Roofs?

As winter sets in, homeowners in cold and snowy climates must prepare to battle the elements. One of the most notorious challenges during winter is dealing with ice dams. These icy barriers that form on the edges of roofs might look picturesque, but they can wreak havoc on your home. Let’s take a look at how ice dams damage your roof, how they form, and how to prevent them.


Understanding Ice Dams and the Damage They Cause

Ice dams are solid ridges of ice that form along the edges of your roof. These dams prevent the proper drainage of melting snow and ice, causing water to accumulate and potentially infiltrate your home. While they might seem benign, ice dams have the potential to become a big issue for homeowners. So, just how do ice dams do their damage on roofs?


Water Infiltration

The immediate consequence of ice dams is water infiltration. As the dam forms, it blocks the natural flow of melting snow, forcing water to back up under the roof covering. This water can eventually find its way into your attic, soaking insulation, damaging ceilings, and even seeping into the living spaces of your home.


Gutter Damage

The weight of an ice dam, combined with its freezing and thawing cycles, can bend, severely weaken, or even tear off your gutters.


Roof Damage

 The water that backs up under the shingles and potentially the underlayment (if your roof has it) can cause damage to the wood sheathing below.  Damaged wood can start to rot and sag and cause your roof to look like it’s bowing.


Mold and Mildew Growth

Beyond the immediate water damage, the lingering moisture and dampness provide a perfect environment for mould and mildew to thrive. Mold infestations must be addressed as soon as they are discovered, as they can be detrimental to your health.


How Do Ice Dams Form?

Ice dams form when a combination of factors combine to create the perfect storm.


Inadequate Ventilation

One of the main culprits behind ice dam formation is insufficient ventilation in your attic. When your attic isn’t properly ventilated, warm air from your living space can get trapped in the attic, causing your roof’s surface to heat. This in turn warms up the snow sitting on your roof, causing it to melt from the bottom.


Snow Cover

Snow is required for the formation of an ice dam. When the roof begins to heat, the snow closest to the shingles begins to melt and the snow on top acts as an insulator. The water then refreezes upon running down to the eaves, which is likely colder than the rest of the roof.


Frozen Temperatures

That melted snow can’t refreeze unless the air temperature is below zero. Ice dams are aided in their formation by warmer daytime temperatures that hover around freezing, followed by nighttime temperatures that dive down into the negatives.


How to Prevent an Ice Dam

There is no better way to mitigate the damage caused by ice dams than to completely prevent them from having the chance to form. Unfortunately, depending on the freeze/thaw cycle, this isn’t always possible and Calgary’s weather, with its infamous chinooks, contributes to a scenario that is sometimes impossible to avoid.  There are ways to lessen the severity though.


Proper Attic Insulation

Ensure your attic has the recommended amount of insulation to prevent heat from escaping from your living space to the attic.



Proper ventilation is crucial for maintaining a consistent temperature in your attic. Take the necessary steps to ensure the warm air is able to properly escape your attic. The addition of exhaust vents will allow more warm air to escape and many homes are under ventilated and “air tight”.  Consider adding ridge venting or vented soffits for maximum breathability.


Snow Clearing

If necessary, safely remove excess snow from your roof, either through your own efforts or by hiring a snow removal company.


Heat Cables

If adding ventilation is not in the budget, heating cables are an option.  These cables can be plugged in when snow starts to accumulate to avoid having it build up. We always recommend addressing the ventilation before using heat cables, but they are an option.


While ice dams certainly look picturesque, the damage they can inflict on your roof and home is anything but charming. When it comes to answering the question of how ice dams damage roofs, proper insulation, ventilation, and roof maintenance are the keys. If you have concerns about your roof being prone to ice dams, don’t hesitate to reach out to us.

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