Hi,
We have a recurring problem with ice dams on one part of our roof.
I've did as much as possible on the insulation front, but still got the ice dams.
What I found works is to get a "roof rake" and use it to pull the snow off the roof above the area where we get the ice dams. Works very well.
Here is one of them:
Amazon.com: Garelick 89421 21-Foot Aluminum Snow Roof Rake With 24-Inch Blade: Patio, Lawn & Garden
It goes surprisingly fast as gravity is on your side.
But, not to practical for two story houses.
Gary