I have a rough-plank gable roof attic space over an old flat tar roof. There is a cement chimney along a now-enclosed wall of this space. I use it for storage. I know I need to insulate the access door, and am wondering if that is all I should do. If I insulate the rafters of this space, how would the heat from the masonry chimney(which I use all winter) affect the humidity---ie: would this create more of a problem to insulate the space? There are no pipes or vents going through to worry about, and the ceiling under the tar roof is insulated, although somewhat minimally. (The house was built in 1933).