The Birth of an Ice Dam
Ice dams are a major winter hazard for sloped roofs in cold climates. They are caused by a thermodynamic imbalance in your attic rather than simply cold weather.
When warm indoor air leaks into the attic through unsealed ceiling penetrations, it rises and warms the upper roof deck. This heat melts the snow on the upper portion of the roof. The meltwater flows down the sloped roof until it reaches the cold eaves, which overhang the unheated exterior walls. There, the water refreezes, creating a thick block of ice along the gutters.
How Backed-Up Water Causes Damage
As meltwater continues to run down the roof, it pools behind the ice dam. Because sloped shingles are designed to shed water running downward, they cannot handle standing water.
The backed-up water forces its way under the shingles, breaking down the adhesive starter strips. During overnight cold cycles, this water refreezes and expands, prying the shingle tabs and nails apart. This expansion damages the fiberglass mat, leading to roof-deck rot and ceiling leaks.
Prevention and Remediation Strategies
To prevent ice dams, ensure your attic is well-insulated and properly ventilated to keep the roof deck cool. If your shingles have suffered winter wind or ice damage, a soy-based rejuvenation treatment can restore flexibility, helping protect your roof against future freeze-thaw cycles. To review local climate tips, explore our state roof cost catalog.
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