How to Prevent Ice Dams

Glistening icicles may look beautiful – but they may signal trouble. That’s because the same conditions that allow icicles to form can also lead to ice dams.


Ice dams are thick ridges of solid ice that build up along the eaves of a home. They form when part of your roof warms up enough to cause snow to melt. The melting water flows down to another part of the roof that is cooler (generally over the eaves or a better insulated part of the attic), and the water refreezes. The ice forms a small dam that becomes larger and larger as more melt water refreezes. Eventually, water backs up behind the dam and works its way under the shingles and into the house below.

Homeowners are left cursing dams that leave them with warped floors, damp drywall, peeling paint, stained and sagging ceilings, torn off gutters, loosened shingles, damaged siding, and soggy – often moldy or mildewy – insulation.

Clogged gutters don’t cause ice dams but they can make a bad situation worse. Rather, a poorly ventilated attic space is generally to blame for these roof wreckers. When the weather warms, it’s a good idea to make sure your attic space is adequately insulated and ventilated; a ridge vent paired with continuous soffit vents will circulate cold air under the entire roof. You’ll also want to seal any gaps that let warm air pass into the attic from the rest of the house. Consult a professional for the best way to avoid ice dams and water damage in your home.

If you have a furnace in the attic, insulation will help – but may not completely prevent ice dams. If you know your home is at risk, you may want to attach special heat cables along the edge of the roof in a zig-zag pattern. The cables, which can be purchased at hardware and home improvement stores, help equalize your roof’s temperature by heating it from the outside. Heat cables must be installed before bad weather strikes.

If you’re already dealing with ice dams, these tips may help improve the situation:

  • Fill the leg of an old pair of pantyhose with a non-corrosive, non-staining ice melter such as calcium chloride. Lay the hose onto the roof so it crosses the ice dam and overhangs the gutter. The calcium chloride will melt through the snow and ice and create a channel through which melted icewater can flow.
  • Do not attempt to chop up ice dams with a hammer or shovel – you’ll just damage your shingles and gutters. Plus, the chunks of ice that fall to the ground can prove dangerous in their own right. Instead, pull snow off the roof with a long-handled aluminum roof rake while you stand safely on the ground. Specially designed roof rakes have wheels that allow for smooth operation and can quickly change the exterior temperature of your roof without damaging shingles.

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