Re: Insulating ductwork?
Originally Posted by keith3267
I can assure you this is not quite correct. I highly doubt the ( air leaky ) crawl space will provide warm enough air to rise and warm the bottom of the floor. Air that stratifies ( meaning it moves ) will not insulate.,only trapped ( non moving ) air would act as an insulator.
Adding insulation to the underside of the floor is most likely required by code and it does work to prevent heat loss from the living space above and help warm the floor to increase comfort.
If your subfloor is either plywood or OSB then you don't require a vapour barrier since those panels are considered a vapour retarder, I would recommend using unfaced batts and applying housewrap to the underside of the joists. The house wrap will be an air barrier preventing cold air drafts from the crawlspace entering the joist bays and reducing the insulation performance of the batts.
One area that's often overlooked is along the base of the wall. Sealing along the baseboard will prevent cold air infiltration and cooling the floor.