Below this post is a great article about preventing ice dams. I wanted to also talk about a couple of other ways you can deal with ice dams if the items in the previous post are not in your budget.
Roof de-icing kits can come in handy with roof areas that are chronic ice dam problems. There are certain cases where the architectural design of a roof does not allow for good positive drainage. Often times a complex roof design will leave you with areas where the snow and ice build-up becomes trapped. If this section of your roof faces North or East it can take days and sometimes weeks before it melts off. This is a good place to use a roof and gutter de-icing kit. This product is basically a heating chord or element that runs inside the gutter and in a zig-zag pattern on the roof. The only draw back is that you must have an outside electrical outlet to plug it into. I would not recommend this for the entire perimeter of your roof but it is effective in those problem areas. I have a couple of customers who have installed this product and have reported that it works great. I have included a couple of pictures that I have taken of the de-icing kits being sold at Home Depot and Lowes.
Jeff Pendergraft/Eclipse Roofing, inc.