I’m finishing an attic and want to know if I need to insulate the attic floor before laying the flooring. If so, which way should I face the paper backing on fiberglass insulation? You talk about facing it toward the heated space, but if both spaces are heated, which way should it face, or should I use nothing at all? -Nicole
The paper facing on insulation contains a waterproof layer which acts as a vapor barrier to keep moisture from condensing when warm and cold air meet. In your case, since both the attic above and room below are heated, you can use unfaced insulation without a vapor barrier, faced insulation, or no insulation at all.
The reasons to consider installing insulation when finishing an attic are to provide soundproofing and keep the heat downstairs when the attic room isn’t being used. If you plan on using faced insulation, put the facing down toward the lower level ceiling, since hot air—and the moisture in it—rises.
Good luck with your project,