About 30 years ago it became fashionable to install the house heater in the attic. This made sense, there is no baseboard heat so you can put your furniture on any wall, and there is no noise inside of the house when the heater kicks on. As with any great idea there can be unintended consequences. The unintended consequences are ice dams. Houses that never had ice dams now do. When the heater kicks on it puts off heat in the attic (along with the many feet of feeder tubes) spewing heat directly on the roof causing the snow to freeze causing ice dams. Your attic floor is insulated, so the heat form the units go directly to the roof.
When we look at a roofing project we look at everything. We will look at the roof, insulation, and venting. By looking at all three aspects we can design a way to minimize the destructive ice dams.