Keep roof drainage systems clear
Keep all drains, gutters, and downspouts free of debris and vegetation that may restrict proper flow.
Consider heat sources
Remove or relocate heat sources that are installed in open attic areas directly under the roof.
Insulate light fixtures in the ceiling below an unheated attic space
Insulate attic penetrations
If you have penetrations into the attic, such as vents, seal and insulate them so that daylight cannot be seen and airflow is minimal.
Install heating cables on flat roofs
Install heating cables on eaves, gutters, and downspouts or around roof drains on flat roofs. This will not remove an existing ice dam, but will create effective channels that allow water to drain off safely.