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How the Weather Can Undermine Your Ice Dam Prevention

I offer a lot of advice on how homeowners can prevent ice dams on their roofs.  I also often give that advice when I’m standing outside with a homeowner, showing homeowners trouble spots on the roof.

Unfortunately, I have never been able to say, “If you take steps A, B, and C, you will never have to worry about ice dams again.”  Although probably 95% of ice dams are caused by factors inside the home like attic bypasses and poor insulation, the other 5% are caused by good old Mother Nature.  There’s only so much you can do to prevent those.

Warmer days, colder nights

Ice dams are possible any time you have above-freezing temperatures during the day and below-freezing temperatures at night.  Water melts on those warmer days, regardless of the condition of your insulation or your attic temperature.  Much of it will run off your roof during the day, but it’s a slow process.  There’s ample time for it to refreeze, which often happens as the sun goes down and the nighttime lows approach.

It doesn’t need to be a downright warm day to cause runoff that leads to ice dams.  It can happen with a 33F day and a 29F night.  Even a 20-degree day with powerful sun can melt a lot of snow.

Radiant heat

The sun won’t go away for the winter, though sometimes it may feel like it.  It will always produce heat.  On days without thick cloud cover, that heat can still melt the snow on your roof.  The heat passes through the snow and gets down to the black, heat-absorbent asphalt of your roofing tiles.  (You may not wear black much during the summer, because you know it absorbs heat rather than reflects it.)  The shingles melt the snow from underneath, and you’ve got runoff and the possibility of ice dams.

Mild days 

If it’s going to get cold, the ice-dam-prevention lobe of your brain should want it to get really  cold. 10-degree temperatures are preferable to temperatures around 31 or 32.

Why?  Because when the temperature is just under or at freezing it only takes a little heat from your attic to pushing rooftop temperatures above 32 degrees.  This means you might have done everything right on your insulation, ventilation, and attic bypasses, and still find yourself facing an ice dam.  The attic will never be as cold as it is outside, no matter what you do.  “Just a little warmer” can fry enough snow to wake the ice dam gods wake from their slumber.

What now?

You’re still not completely helpless in the face of weather.  If you rake all or most of the snow off your roof you’re removing most of the raw material for the ice dam.  If there’s nothing for Mother Nature to melt, there’s no ice dam.  Of course, it’s hard (and often impossible) to get all the snow off your roof with a roof rake.  Still, you’ll reduce significantly your chances of getting an ice dam if you take up the roof-raking habit and stick to it.

You can also watch the weather closely.  If you think the conditions are prime for a weather-created ice dam, consider turning the heat down a little more that day.  If you normally keep it up at 78 maybe take it down to 70 (if your significant other doesn’t wring your neck).  This will further reduce the amount of heat that may contribute to ice dam formation.

Again, there is no perfect solution.  Bad luck can befall even the most ice-dam-proof home and ice-dam-fightin’ homeowner.  The good news is doing everything in your power is almost always enough.

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