Steve writes from Villa Park, Illinois: "I am hoping you can assist me with a few quick questions on insulating an unfinished attic/crawl space. I own a home that was built in 1923. While re-wiring the front half of the house, I discovered the insulation in the floor of my unfinished attic was quite old and in poor shape. This explains the high electric & gas bills during my 1st year of living in this home. I am about to re-insulate the floor and an inside wall of the 10' by 30' space. The floor has typical joists (I think 2 x 16 material) and is above my living room. The inner wall is 2 x 4 construction and divides the attic from an upstairs hallway and bedrooms. The roof is uninsulated and has two vents in it (one on either end). Your website indicates that I need an R-value of 49 for my area (Zip Code 60181), however you only sell insulation that goes up to an R-factor of 38. I would assume this means I need to put down two layers of insulation. My question is can I put two layers (one on top of the other) between the floor joists? I do not want to do a criss-cross pattern since I plan on decking over the insulation/joists and use the space for storage. If I can do this, would I use unfaced insulation on the bottom, and faced insulation on the top? Also, what are the advantages/differences to foil vs. paper facing? Also, is there any advantage of insulating the roof joists, even though it is a vented crawl space? Or, is this just a waste of money? Finally, should my roof vents be closed/sealed for the winter?"

Answer: For the attic floor, fill the cavity with unfaced insulation without compressing the existing insulation. Compressing fiberglass insulation will cause it to lose R value.

For the interior wall, if the studs are 2" by 4" you can install high density fiberglass insulation with an R-value of 15.

Don't be concerned about the facing. With the floor, you are putting insulation on top of existing insulation and you don't want a facing between or on top of the insulation. For the wall, an interior surface is already in place and will prevent you from attaching a facing properly. You shouldn't have any moisture problems with proper ventilation. Keep the attic vents open in winter and summer; ventilation is important to help moisture and excessive heat escape from enclosed areas below and at the top of a home. Ventilation helps prevent damage to building materials and structural components such as the roof.

There is no reason for insulating the attic rafters unless you are planning to finish the attic for living space. If not, it would be a waste of money.