We are in Minneapolis with a 1923 Tudor house. Last year was our first winter in the house. We had bad ice damns last year and there is plenty of evidence it has had problems in the past. The second floor is a full story and consists of a shed dormer addition with no venting that I can see. The rest/original of the roof has minimal venting due to lack of (none) eves. There are only pots, but no soffit venting. Half of the story is unconditioned attic is accessible and is on the same floor as the living space. Access through a full size door. There is a tall knee wall separating the two spaces. There is a strip of inaccessible attic space along the ridge of the house that has a couple of vents as well. The bath and one bedroom have a 45 degree wall/ceiling (against the roof) between the accessible attic and inaccessible attic below the ridge. Before we purchased the home an AC unit (air handler and condenser) was placed/retrofit in the unconditioned space. There is a mess of fiber glass in the attic against the knee wall and blown in cellulose on the floor. I believe this is the cause of most of my issues. My question: can I condition the attic and convert it to an unvented roof with closed cell foam, while leaving the adjacent living space original? Is mixing vented and unvented a bad idea? The only way to access the whole roof would be to remove some of the sheathing, but I would like to avoid that if possible. Thanks in advance. Joe.