There is a TON of info out on the WEB that comes up when you use one of the popular search engines to locate info on this subject. If you go to Alta Vista Search, and enter in, +"ice damming" and press , you'll get a ton of sites that mention the phrase, 'ice damming'. If you're not familiar with web searches, this is a good time to grab a friend or try and learn on your own. In the mean time, if you need something right now, go to Smart Home, peruse the next few pages at the site, and you'll get 1 perspective on ice damming. As I mentioned earlier, there are TONS of sites to visit on this subject.
So, I'll spare any details on your question here because this is 1 question that is best answered by reading info at a few WEB sites. Good luck! Certainly, if you have any more questions, post 'em up!