We use our finished attic space for storage, extra sleeping, and for a photo studio. We have blown insulation under the attic floor and above the ceiling in the finished space. However, we have 2 small rooms that we use for storage and they are not insulated. Last winter I noticed frost on the roof sheeting and on the nails in the unfinished rooms. Our house is 100 years old and the soffits are the orginal so they aren't vented. We do have a small gable vent above the ceiling in the finished part of the attic. We have ice dams on the roof on the south side of the house in the winter. How do we fix the problems of ice dams and frost on the roof sheeting and still be able to use our attic space? There is a gas heater in the finished attic space. We live in Wisconsin.