Sol, from Sudbury, Ontario, has terrible ice dams, as you can see in the photo. They are directly over his bay window. Take a good look at the house design. The bay window comes right out to the edge of the roof, preventing any possibility of any ventilation up over this area. In addition, because of the angle of the roof and the jut-out of the bay window, there must be very little insulation over this area. These two things, together, will guarantee the melting of the bottom of the snow pack and the creation of ice dams. The only solution, short of raising the roof a foot higher, is to put in de-icing cables like Easy Heat from Heron Cables and paying the electrical bills.
This house design is born out of pure ignorance, whether it was originally built this way, or someone innocently simply extended the living room. Overhangs, soffit ventilation, space for insulation are all there over the edge of the house for a reason, and if you violate these things, the house will fight back, with ice dams and wet ceilings. Unfortunately many carpenters are quite competent at cutting boards and fitting trim, but have no concept of how a house works. Sorry about that Sol.