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Kitchener-Waterloo Home Maintenance - Preventing Roof Ice Dams



Roof Ice Dams can Cause Major Home Damage in Winter

By: William Woolsey, Brookside Roofing
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You've seen it many times - a mass of heavy ice collecting at the eaves of a roof. But did you ever wonder why these hazardous (and dangerous) ice masses and icicles form? The answer is simple: Trapped heat in your attic melts the snow on your roof. The melting snow then dribbles downward to the edges of the roof and re-freezes, over and over again, continually adding more ice mass, and eventually causing havoc to the structure of your roof.

You might not know the extent of the damage until it is way too late: Damage such as

  • warping and detachment of eavestroughs,
  • fascia board damage,
  • roof wood rot, and
  • melting ice leaking into your house resulting in drywall and plaster stains.

Why does this happen?
You might be surprised by the answer. The power of ice is tremendous. When water freezes it expands and creates a huge force that pushes against anything in its way. This powerful force can bend steel like bubble gum. Imagine this huge level of pressure pushing against soft materials such as wood, aluminum, asphalt shingles, or bricks, concrete, and stone walls (all easy prey for ice dams). Clearly, the damage caused can be substantial.

What is the answer?
The only lasting solution to prevent roof ice damming is proper roof ventilation.
Why? Because proper roof ventilation removes the trapped heat in your attic (the very heat that causes ice dams) and studies prove that a cool attic during winter stops the thaw/re-freeze cycle and thus stops the melting snow from re-freezing at the roof edges.

But how does roof ventilation specifically prevent ice damming? The answer is to create an attic temperature that is close or equal to the temperature outside of the attic using specific roof/attic ventilation procedures such as soffit roof ventilation and ridge roof ventilation. Let's expand on these two types of roof ventilation.

Soffit ridge ventilation is a system of openings along the perimeter of your roof. These openings are referred to as intake vents. Their purpose is to allow air to freely enter the underside of your roof which will then travel upwards to the top of your roof directly beneath the roof boards. Ridge ventilation (at the top of your roof) will now complete the process. Ridge ventilation is a continuous vent that is installed along the entire ridge (or top) of your roof, referred to as exhaust vents. Using the wind, ridge ventilation sucks air out of the attic using an energy-free power source, namely Mother Nature. Wind creates a negative pressure that effectively pulls new air into the soffit vents along the entire surface of the attic roof boards, which is then expelled out through the ridge vents.

This creates significant maintenance benefits for the home owner. With fresh air constantly being pumped throughout your roof's attic spaces, any trapped heat is removed. When this heat is removed, the temperature of your attic becomes close or equal to the outside temperature (of course, with good insulating, the house stays warm and does not lose het to the attic). The result is no melting snow to will drip down and re-freeze at the eaves of your roof.

Further improving results
Two final suggestions: first, ensure that the ridge vent is baffled. A baffle is simply a small curve on the ridge vent itself that creates the negative pressure that sucks the trapped heat out of your attic much more efficiently than ridge ventilation without baffles. Without this baffle, the effect will be minimal. Secondly, the area of soffit intakes and ridge ventilation area should be about the same, so that air that flows in can be exhausted. If one is smaller than the other, air flow will be based on the smaller opening(s).


William Woolsey is a roofing and attic ventilation expert with Brookside Roofing, serving Greater Toronto Area home owners for 25 years.

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