My house is a "garrison" colonial...second floor sticks out farther than the first floor walls, with a 1-1.5 foot overhang front and back. A while back, I discovered that this "soffit like" area, under the overhang, is only covered by a thin sheet of vinyl siding, attached to the underside of the 2nd floor joists. outside air (I believe) just flows in and out of the ceiling/floor cavity. I know that in the morning, when I put my feet on the floor, it is icy-cold. I'm thinking that the warm air that is piped up to my second floor is being sucked right out of the house through this flaw. (not the "air" itself, but the heat, through conduction). So, the question is, what should I do about it? I'm thinking that the thing to do is to remove that vinyl soffit/cover/whatever you call it on the underside of the joists, stick an appropriate chunck of fiberglass bat in there (just the length of the overhang area), then cut foam-board insulation to fit between each joist to plug the gap, and seal it with caulk or spray-foam to make it air-tight. I don't know how they normally sheath a garrison...like when they don't use vinyl siding, but in this case, you couldn't just nail a long 1x board...like the roof's soffit, say...because then the vinyl siding wouldn't fit back over it. So the only way I can think to seal up the holes is to "plug" them w/ foam board. the vinyl will go back exactly the way it was.