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▣ How to Prevent an Ice Dam

posted by Steven Listino on January 17th, 2011 at 9:49 AM

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An ice dam is a ridge of ice that forms along the lower edge of a roof and blocks melting water (snow) from running off the roof. Over time, the dam of ice builds up as more and more water freezes and the runoff water pools behind the dam--eventually working its way under the shingles right into the roof structure--and even down into the house. Ice dams are caused by heat loss from the house, so in newer construction with good insulation and proper attic ventilation--ice dams aren't much of a problem. However, in older homes--ice dams remain a constant problem and cause millions of dollars worth of damage in northern climates. Here's how you can prevent an ice dam on your roof.

  • 1. Understand that ice dams are caused by heat loss from inside your house. Heat rises into the attic, warms the attic and the underside of the roof and helps melt snow when the warm sun is shining. To prevent ice dam formation in older homes, you need to prevent this heat loss.

  • 2.  Ensure your attic insulation is up to modern standards. Modern building codes require attic insulation to be at least R 38 or even higher. This is approximately 12 inches of fiberglass bat insulation.
  • 3. Allow cold outside air to flow through your attic. A properly ventilated attic has open soffits (under the eaves) where outside air can come in and upper vents (either individual roof vents or a ridge vent) that allow the cold air to move up underneath the roofline and out the top. This air movement keeps the roof cold and prevents an ice dam from forming.
  • 4. Install baffles between the roof joists to stop any insulation from migrating over the top of the soffits, blocking the air and preventing proper air movement.
  • 5. Insulate and seal all openings from the house into the attic. This includes plumbing stacks, heating ducts, attic access hatches, pot lights and ceiling fixtures. Any and all of these openings into the attic will allow warm air into the attic raising the temperature to help melt snow on the roof.
  • 6. Prevent a large buildup of snow on your roof. A roof rake will allow you to pull any snow buildup off of your roof while you stand safely on the ground.


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