I want to insulate in between joists to reduce heat loss to an unheated basement. I had in mind to use fiberglass insulation. My problem is how to keep the insulation in place. SInce it is underneathe the floor joists it will fall down, short of putting in a ceiling I haven't found another solution. Is there an easy way to hold it in pllace or is there another type of insulation (Rigid) which would solve this problem.