Ice Dams

Ice Dams

Overheard at Home Depot: “…I had someone rip off all my gutters so I won’t have any ice dams this year.

Wow. This individual paid someone for the wrong solution. They may have also created some basement water issues for themselves–though that’s a subject for another day. While there is plenty of misinformation out there about ice dams, the building science is pretty clear. Gutters don’t create ice dams. Period.

How Ice Dams Are Created

When I’m explaining ice dams to a customer, I look around for a garden shed on their property or a neighboring yard. It’s a concrete way to illustrate how ice dams are created. I ask people if they ‘ve ever seen ice dams on the shed. Of course, the answer is always “No”.

Ice dams typically form only on heated structures. Ice dams are created when:

  1. there is roof snow to melt
  2. a source of interior heat exists to melt the roof snow
  3. temperatures are cold enough to freeze melted snow into ice.

Here’s the process:

  1. Heat from inside the house migrates to the attic, warming the roof deck above the heated area of the house
  2. Snow in contact with the roof deck melts and runs down the roof edges
  3. At the roof edges (the eaves), the melt refreezes because this area is outside the house heat envelope
  4. This “melt – freeze” process repeats, creating a mound of ice – the ice “dam”

After Ice Dam Has Formed

  1. Snow continues to melt, eventually creating a pool of liquid water above the dam
  2. The pool of trapped water seeps under the shingles and into the house.
  3. The water runs down the inside of the structure, wetting insulation, wood framing, and sheetrock.

Here’s a pool of water behind an ice dam:

Ice DamageThis water had already gotten under the roofing shingles, soaking all of the attic insulation, the sheetrock ceilings, and some of the interior walls – a serious mess.

It’s not gutters. The issue is heat moving to a place where it shouldn’t be (your attic).

For those looking for an in-depth explanation of ice dams, see this article from Building Science Corporation.

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