Ice dam cometh?

Illustration of an ice dam on a roof.

I have a weird fascination with icicles. During the winter, I like to travel around certain neighborhoods and scope out the size of icicles hanging off of houses. While they can appear to be "beautiful," I recently learned how truly ugly they can be. Not only are icicles a sign of inadequate attic insulation, it could be a start of a serious problem — ice dams.

What is an ice dam?

According to the University of Minnesota, "an ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow from draining off the roof."  That water will back up behind the ridge and can leak into the home, damaging walls, ceilings and insulation.

What causes an ice dam?

That same article from the University of Minnesota contains a very detailed diagram as to how an ice dam can form. Here a simplified diagram I created that illustrates what happens.

First the house must have snow on the roof and the temperature of the upper part of the roof must be above 32 degrees for an extended period of time (a result of heat loss in the home), and the lower portion of the roof must be below 32 degrees for an extended period of time because of the temperature outside. The snow on the roof melts and gets trapped behind an ice dam that formed on the overhang, possibly involving a frozen gutter. The trapped water has nowhere to go except through your roof and into your home.

How do you prevent an ice dam?

The best way to deal with ice dams is to prevent them. A short term solution is to rake the snow off of your roof, so there's nothing that will freeze into a dam and nothing that can melt. A long term solution is to make sure your ceiling and attic spaces are airtight, well insulated and cool. That will prevent heat loss in your home and help maintain uniform temperatures on your roof.

I received my ice dam and insulation education a couple of months ago when we had an energy audit and insulation upgrade in our house. Every year, we had some spectacular icicles above our kitchen, heater and dryer vents. We finally decided that we had to do something about it. Not only was our attic space leakier than a balloon with a hole in it, the little insulation that was there was completely inadequate. After having the work done, we noticed that our home felt warmer within one day. And those icicles that always appeared off the back of our house have vanished.

Winter's not over yet and in some parts of the country, it has just begun. Consider speaking with a contractor to make sure the insulation is sufficient in your home for the icy months that may come.



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