Bill writes from Rochester, Michigan: "I have a half basement and half crawl space. When I bought the home the crawl walls were insulated with batts and the floor is covered with plastic. The house above the crawl still gets very cold in the fall and summer. We have hardwood floors, so it gets really chilly. Can I insulate the ceiling/underside of the floors? If so what should I use? I heard I may want to seal it off by stapling plastic to the floor joists after putting insulation under the floor? Is that recommended?"

Answer: Yes, you can insulate the underside of floors under a crawl space. I recommend using unfaced PINK FIBERGLAS® insulation to fill the entire cavity between the floor joists. You should not use plastic film after the fiberglass has been installed because the plastic would create a double vapor barrier. Also, plastic is never recommended in below-grade applications. Plastic is too strong of a vapor barrier in high moisture areas such as crawl spaces and basements.