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This is my first winter in my current house in northeast USA with lots of snow. There is a ~2ft overhang on the roof all around the house (for better or worse, as noted in another question with pics of roof). As I smack large icicles off the edge of the eaves to avoid them getting too big/heavy/hazardous, I wonder if we'll have ice dams at this house.

The attic could use more insulation and ventilation but it does have some, so that has me on the lookout for ice dams. So far we have tons of snow accumulating on the roof (including the peak) and icicles but no visible bulks of ice on the gutters/roof edge.

I'm wondering how the long overhangs would affect ice dam formation. One thought is that if an ice dam forms and water is sitting above it, the overhang could be damaged (and the rest of the roof due to the weight) but I'd expect water would not dam far up enough to go into the house/walls. Another thought experiment tells me that the overhanging 2ft of roof will be far colder than the rest of the roof (being exposed to outside air beneath it rather than attic air), which could lead to very large and heavy ice dams?

Looking for some expertise/experienced views on this. Thanks in advance.

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Longer overhangs could impact ice dam formation, but it does not seem to be a significant factor. As this page from the University of Minnesota outlines, heat loss through the roof is the big contributing factor. They even go further and say that air leakages around light fixtures and such on the ceiling of the top story are the biggest culprits. Nowhere on that page is the size of the roof eaves even mentioned.

Longer eaves could increase the size of the ice dams, possibly preventing or delaying damage to the structure of the house. Or the water may freeze before it reaches the edge of the roof, as if the eaves were shorter. It probably depends on the temperature differential on the roof and how cold it is outside.

In any case, icicles are a sign of heat loss through the roof, and corrective action is advised. It may be as simple as adding insulation in the attic, but may involve sealing up areas around light fixtures, moving exhaust ducts (e.g., driers), using fireplaces less, etc.

  • Couldn't icicles be a normal result of snow melting, and a good sign that snowmelt is flowing off the roof edge rather than accumulating on the roof edge? – cr0 Jan 9 '18 at 20:15
  • If the temperature has been high (above freezing) then possibly. The size of the icicles in that case should be proportional to how long the temperature has been above freezing. You definitely want the snowmelt flowing off of the roof rather than damming up, but you only get dams when the outside temperature is below freezing and there is something warming up the snow on the roof. – mmathis Jan 9 '18 at 20:45
  • Got it. Today and tomorrow the temperatures are above freezing (for the first time in a while). There were icicles forming during freezing temps but I didn't notice ice dams. This morning is the first time I noticed ice dams (a wall of ice forming on the edge of the roof). Hoping warmer temps for at least 2 days will help resolve it, but later today I'll also toss some 'salt blocks' up on the roof to create channels for water to flow out of the dams. – cr0 Jan 10 '18 at 13:47

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