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SESK: Stuff Everyone Should Know · sesk.info/home-ice-dam

What mainly causes ice dams on a roof?

Heat escaping from the house melts snow unevenly on the roof.

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  1. Gutters that are too clean
  2. Heat from the house melting snow unevenly ✔
  3. Too much snow alone

Why: Heat leaking from the house warms parts of the roof, so snow melts, then refreezes at the colder edge. That ridge of ice traps water, which can leak into walls and ceilings.

Huh, didn't know that: Ice dams can lead to mold and mildew, so dry any wet areas right away.

The dad joke
Did you see that all the snow and ice are melting? Yes, I thaw!
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References

Answer: Heat from the house melting snow unevenly. Heat leaking from the house warms parts of the roof, so snow melts, then refreezes at the colder edge. That ridge of ice traps water, which can leak into walls and ceilings.

  1. UMN Extension: Ice dams extension.umn.edu/node/7346
    It is primarily heat flowing from the house that causes the nonuniform temperatures of the roof surface leading to ice dams.
    Checked 2026-10-10.
  2. ENERGY STAR: Attic insulation project www.energystar.gov/saveathome/seal_insulate/attic-insulation-project
    Combined with attic air sealing, it can also help to alleviate the formation of dangerous ice dams in the winter.
    Checked 2026-10-10.

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