As far as I know, it’s important to have outdoor air that flows under the roof in cold climates to avoid ice dams. Otherwise insulating the roof deck is just fi

As far as I know, it’s important to have outdoor air that flows under the roof in cold climates to avoid ice dams. Otherwise insulating the roof deck is just fine and possibly even advantageous. An unconditioned attic is not so great because it’s difficult or impossible to do a good job of avoiding leakage into the living space. Also, any mechanical equipment in the attic would like to be in conditioned space.