What Are Ice Dams?
Ice Dam Diagram from Michigan State University
Ice dams are a ridge of ice that forms along the edge of the roof that traps melting snow. They are caused by the combination of heat loss from the home through the attic, snow cover, and freezing outdoor temperatures.
When heat is able to accumulate in the attic, it causes the upper portions of the roof to warm up. This melts any snow gathered there. The water from the melted snow then runs down the roof toward the edge. As it nears the edge, the temperature of the roof drops, allowing the water to refreeze before reaching the gutters. This cycle leads to the formation of a ridge of ice. As the ridge grows, more and more water is trapped behind it, hence the name ice dam. The pooling water is then able to infiltrate the shingles and enter the attic through any small cracks or gaps.
Oh No, Ice Dam(age!)
Ice dams can cause damage to a home in several ways, each of which is expensive to resolve. Firstly, when water is able to seep into roof structures and attics, water damage is nearly inevitable. Mildew, mold growth, and costly wood rot can take root, leading to expensive remediation costs. If these issues are allowed to worsen for an extended period, the water damage will continue to spread to the other areas (think warped floors and ugly water stains on the ceiling) and damage the contents of the home. Other potential damages include roof failure and deterioration of gutters from excessive snow and ice dam weight.
Reducing the Risk of Ice Dams
Ice dams can lead to costly damage to roofs and home structures.
It can be extremely difficult to rectify the situation once an ice dam has formed, so it’s best to take action beforehand to protect your roof and house:
- Clean gutters before snow arrives. Thoroughly clear them of sticks, leaves, and other debris.
- Use a roof rake to reduce the amount of snow accumulated on the roof.
- Clear snow and icicles from gutters regularly.
- Improve attic ventilation and insulation.
The surface temperature on a roof is higher if the attic is poorly ventilated or insulated. This, in turn, leads to snow melting and starting the ice dam formation process.
Ice and Water Shields
Adding ice and water shields during re-roofing can help prevent water from entering the house and mitigate the effects of ice dams. These self-adhesive membranes work as a waterproof barrier beneath the shingles. When ice forces water under the shingles, shields prevent it from reaching the interior and causing damage. To make them more effective, Ellen recommends installing the water shields a few feet from the edge of the roof.
An ice and water shield is a waterproof membrane that is installed beneath the shingles to protect the more vulnerable areas of a roof. These shields are adhered to the roof deck, typically in 3-ft wide strips, along the eaves and valleys of the roof and other key spots such as around chimneys and skylights. Since ice and water shields must go below the shingles, these must be installed during re-roofing.
Why not just install ice and water shields across the entire roof? Ice and water shields are not typically installed across an entire roof as they can form a vapor barrier. This traps moisture between the membrane and the roof deck and can lead to condensation and water damage. If shields are going to be installed across the entire roof, proper attic insulation will be critical in preventing vapor barrier issues.
