you may be correct, especially when it rains in the winter. Regardless of why, an ice damn can cause problems. Typically older homes without roof ventilation and poor insulation are the culprit. When your heat from the living space escapes into the attic excessively, it will melt snow on the roof which in turn will run down the roof till it hits the eve's (over non-heated area) and freeze. The correct amount of insulation will retain the heat in it's proper location. Ventilation will allow the heat loose to exit the attic without melting the snow. A minimum of R-38 in the attic is recommended.
You very well may be fine with your insulation and ventilation but it cannot hurt to check because if not, you will be dumping money "out the window" so to speak. I would say by what I saw at my house this winter so far that I have severe heat loss and in my attic. My insulation barely covers the 2x6 ceiling joists which is roughly a R-19 (poor) Most houses in da UP are not insulated at all, go figure, we burn wood and heat our houses around 75 degrees easily and you'll see huge ice sickles forming, getting bigger and bigger, sometimes creeping up the roof. It's when it gets under the roof and creeps where the damage occurs
