Signs your roof is vulnerable to ice damming

Prevention begins in the attic

Q: I have a question about attic insulation. I was under the impression that attics should remain ventilated and uninsulated to prevent the buildup of ice dams. Can you clarify?

I have a walk-up attic with floorboards. There is insulation under the floorboards, but nowhere else. There are two walls (inverted v-shape) at the two ends of the house, and in between just the slanted roof down to the attic floor. All the wood framing is exposed. There are two circular vents in the roof.