An ice dam forms when heat from the house melts snow on the roof, and the meltwater refreezes at the cold eave and backs up under the shingles. University extension guidance points to attic air sealing, insulation and ventilation as the cure. Raking snow off treats only the symptom.
Key takeaways
- Heat from the attic melts snow from below; the meltwater refreezes at the cold eave.
- Water that backs up behind the ice can get under shingles, even when it has not rained.
- Air sealing, insulation and ventilation address the heat. Raking only removes the snow.
- Do not chip ice off a roof or climb onto an icy surface.
How does a thaw in Kenosha turn into a leak with no rain?
Warm air from the house melts snow on the roof, and the meltwater refreezes where the eave stays cold.
Snow on the roof melts from the warmth rising through the attic. The water runs down to the eave, which stays below freezing, and freezes into a ridge of ice.
Water that backs up behind that ridge can work under the shingles and reach the walls, even on a day with no rain. That is why a leak shows up in a thaw and not in a storm.
What cures an ice dam?
Air sealing, insulation and ventilation address the heat that causes the melt in the first place.
University extension guidance from several states describes the same sequence: seal the gaps that let warm air reach the attic, add insulation to the attic floor, and make sure the attic is ventilated.
The sources used for this guide include no Wisconsin extension figures, so this guide gives no R-values or ventilation ratios. An inspection can show what the attic needs.
Why does raking snow not solve it?
Raking removes some snow and eases the load, but it leaves the heat that melts the snow.
Raking can reduce the weight and the water that backs up, and it is a reasonable short-term step when it can be done safely. It does not stop the melt that makes the dam.
Work from the ground with a long-handled rake where that is safe. Do not climb onto an icy roof to do it.
Frequently asked questions
Is ice on my gutters always an ice dam?
Not always. Ice that builds up along the eave after a thaw is a sign of an ice dam. A technician can check the attic to see whether warm air is melting the snow from below.
Should I chip ice off the roof?
No. Chipping damages shingles, and the work is a fall risk. Ice that is out of reach should be left to a technician, and any water inside the house should be dealt with first.
Does an ice dam mean the roof needs replacing?
Not necessarily. Ice dams are often an attic heat and ventilation problem. An inspection shows whether the shingles, flashing or decking were damaged by the water.
This guide is general information for Kenosha County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.