Ice dams, and ensuing roof leaks, can occur on almost any home in the winter if certain unique weather conditions are present. The photo to the left shows a common ice dam forming. The thawed slush travels down to the edge of the roof, where it re-freezes before leaving the roof. The trough at the upper portion of the dam holds the water and slush. Some freezes, building the dam even larger. Other moisture will find its way under the shingles and into the home.
Ice dams occur when snow accumulates on the roof to such an extent that it creates an insulating blanket over the roof and attic. They can also occur during minimal snowfall if the attic has insulation which is insufficient or improperly applied, and if there is insufficient ventilation in the attic. Proper ventilation can be blocked by heavy snow.
If the attic becomes warm enough to heat the roof deck to 32F or above, snow will melt. If the soffit regions (roof overhangs) are cooler than 32F, the melting snow will re-freeze over the soffit, creating ice, which will grow into a mass similar to a dam, blocking melted snow from running down the slope. This snow melt will then back up, usually finding its way into the home through the smallest openings in the roof structure.
There are ways to eliminate or greatly reduce ice dams. Methods include properly insulating and ventilating the attic, and removing snow from the roof as it accumulates. Snow removal should be performed with proper snow roof rakes, and always from the ground.
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| Ice dam beneath bathroom vent |
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| Ice dams can also occur beneath sources of warmth, such as the bathroom ventilator shown in the photo to the left. In this case, use of the bath vent melted snow below the vent, then as the snow melt traveled down the slope, quickly refrozed. As the dam increased in size, the water pooled around the hood, eventually finding its way into the roof system and into the living areas inside. Here, removing the snow cover, and carefully creating a channel for any remaining moisture to travel past the dam, stopped the leaking.
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| How not to get rid of ice dams.
Take a close look at the photos on the left. As I climbed the ladder to inspect the roof of this home, I noticed a series of gashes (see the upper photo on the left) in the shingles a bit above the edge of the roof. As I went up the roof and looked over the ridge, there was the splitting maul still laying on the roof. Busting ice with a maul on a roof is hard work and usually does serious damage to the roof.
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