Roof Ice Dams

If you drive in the colder climates, you have likely seen this highway sign, “CAUTION ICE ON BRIDGE”

So, what does that have to do with my roof?

Let’s start with some basics. The ground does radiate some heat, even in winter. Even when the outside air temperature is below 32 degrees Fahrenheit, mother earth continues to radiate its heat to the earth’s surface and does battle to delaying ground frost. Eventually, the air temperature continues to drop until frost occurs. Now let?s cross that bridge. The air surrounding the bridge, including under it, is far from mother earth?s heating influence. So, the cold air is going to do its job. Any water or moisture can now freeze that is on the bridge surface. Keep this thought while we go to your winter climate home.

It’s two o’clock in the afternoon and look at all that beautiful snow on your roof. As you enjoy the warmth inside your home, the heated air rises against the ceiling and actually raises the air temperature of your attic. Together, the warming attic and the sunshine beading down on your roof (about 38-40 degrees Fahrenheit) will start to melt the snow.

Now, your roof eaves tell you the snow is melting by the constant dripping. Then, the sun goes down and so does the air temperature. The constant dripping at the eaves of your roof slows down and starts to freeze. Remember why the ice on the bridge formed? The same applies here, your eaves are just like the bridge. There is freezing air just waiting for that next drip. Actually, this is the beginning of icicles, destructive, roof damaging icicles. As the icicles get longer and longer, they also get wider. To make matters worse, the warm home continues to melt the snow on top of the roof. The melting snow rolls down to the eaves and collects against the eave gathering ice. This is known as ice damming.

The destructive ice starts to work its way back up the roof and under the shingles. Your roof protection has been compromised. It’s just a matter of time before this repeated scenario makes its way, as a ceiling stain. So, what can be done to reduce destructive ice damming? Insufficient attic ventilation and inadequate attic ceiling insulation are the first things to look for. The proper amount of ceiling insulation will minimize the upward heat loss from the living area, which will then allow the attic ventilation to do its job.

As far as knowing if there is sufficient ventilation in the attic, you can simply record the outside air temperature and then the attic temperature. Ideally, your attic space should be within 15 degrees Fahrenheit of the outside air temperature. The overall goal is to influence the accumulated snow on your roof via effective ceiling insulation and ample attic ventilation, so the snow collectively and uniformly melts off. Depending on your attic configuration, there is a formula to figure it out. However, it’s then time to call a qualified licensed general contractor.

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