I've noticed that when my childrens' bedrooms are closed and the stove is heating the house exclusively at night, that one of the bedrooms is noticeably colder than the other by the time it's morning. Below the cold bedroom is an unfinished space with the furnace, and it stays approx 55F during the winter. Below the other bedroom is a bathroom that has insulation and drywall on the joists. Would it help at all to insulate the joists below the cold bedroom? Was thinking kraft faced R-19 with the flaps, easy to staple up. Kraft faced so the liklihood of fiberglass flying around is less. Thanks in advance!