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How to prevent ice dams

An ice dam is the attic's heat melting snow on the roof. Seal the attic, insulate it, keep the vents open, and pull snow off the lower edge.

1 min read

What an ice dam is

Snow on the roof melts where the roof is warm, and the water runs down until it reaches the cold edge over the eaves, where it freezes. The ice grows into a dam, the next melt backs up behind it, and the water works under the shingles into the attic or the walls. NDSU Extension says they are most common when there is snow on the roof, heat is escaping through it, and it is just below freezing outside.

The fix is a cold roof

"The key to limit or prevent the formation of ice dams is to ensure your roof is constructed properly with sufficient attic insulation and enough ventilation to keep the roof near outdoor temperatures," says Ken Hellevang, an engineer with NDSU Extension.

In the attic

  1. Seal the holes first. Heat leaks into the attic where plumbing, heating and electrical lines pass through, around recessed lights, and around the hatch or ladder. ENERGY STAR's attic air sealing project covers how, and says to do it before adding insulation.
  2. Then insulate. NDSU Extension says attics in northern climates need roughly 15 inches of blown-in insulation, about R-50.
  3. Keep the air moving. Some heat always reaches the attic, so vents in the soffits and at the ridge or gables carry it out. Baffles hold insulation back from the soffit vents so they stay open.

On the roof

After a heavy snow, pulling the snow off the lowest few feet of the roof with a roof rake, from the ground, takes away what a dam forms from. NDSU's engineer warns that heat tape on the roof treats the symptom, not the problem.

When to call someone

A dam already leaking into the house, or a roof you would have to climb onto, is work for a roofer.

The steps for roof and eaves

  • Make sure the roof vents are openSoffit, ridge or gable vents let the attic's heat out before it melts snow on the roof. Leaves, paint or insulation pushed against a soffit vent can close it.QuickSource
  • Pull snow off the lower edge of the roofIce dams tend to form low on the roof, over the eaves. Clearing the bottom few feet after a heavy snow, with a roof rake from the ground, gives the dam less to work with.A projectSource
Check them off on the houseThe whole checklist

Sources

  1. NDSU Extension: Reduce ice dam and icicle damage ag.ndsu.edu
  2. ENERGY STAR: Attic air sealing project energystar.gov
  3. ENERGY STAR: Seal and insulate with ENERGY STAR energystar.gov

Drafted on October 26, 2026 with a language model from the pages listed above, each opened that day, and sampled by the editor after publication. Every figure is computed by the same code the tools run, and a test fails the build if one stops matching.

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How to prevent ice dams | Winterize House