Do long roof overhangs influence ice dam formation?

Question

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.

Answer 1

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.