Ice Dams 101: Why They Form and How to Prevent Roof Damage This Winter

If you've lived in Wisconsin for a winter, you've seen ice dams: the thick ridge of ice along the edge of a roof with icicles hanging below. They look harmless, but they're one of the most common causes of winter leaks we see.

How they form: heat from your living space escapes into the attic and warms the roof deck. Snow on the upper roof melts, runs down to the cold eaves, and refreezes. That ice builds into a dam, and the meltwater behind it backs up under the shingles and into your walls and ceilings.

The real fix is in the attic. Ice dams are a heat problem, not a gutter problem. Adequate attic insulation keeps heat in your living space, and balanced ventilation with soffit intake and ridge exhaust keeps the roof deck cold and even. Sealing air leaks around light fixtures, attic hatches, and plumbing stacks makes a big difference too.

Ice and water shield is your backup. Wisconsin code requires a waterproof membrane at the eaves extending inside the exterior wall line. On a new roof, we install it at eaves and valleys so if ice does form, water can't get in.

Clean gutters help. Gutters packed with leaves freeze solid and make ice dams worse. A fall cleaning is a simple, inexpensive step.

What to do if you have one now: use a roof rake from the ground to pull snow off the first few feet of the roof. Never chip at ice with a hammer or shovel, since you'll damage the shingles. Calcium chloride in a sock laid across the dam can cut a channel for water to drain. Avoid rock salt, which damages shingles and plants.

If ice dams come back every year, have the attic evaluated. Fixing the cause is far cheaper than repairing water damage every spring.