Johnny writes from Albuquerque, New Mexico: "My house is about 65 years old. I have 2x6s in the attic with 3" to 5" of blown fiberglass, no vapor barrier at all. All inside ceilings are plasterboard (sort of a cross between plaster and drywall? I forgot the trade name some time ago), with many layers of latex paint over that, I'm sure. I have 3 passive gable vents maybe 20"x15" each for ~1200sqft of attic. No eave or peak vents at all.

I'd like to add insulation, and I've read arguments for and against kraft faced batts with regard to moisture retention, etc. So, put new fiberglass with kraft facing under the old, or just fill up to the top of the 2x6s with unfaced and then put unfaced R30 over that, or take it all out and start over, or what? It seems to me that adding a lot of insulation, like I'm thinking of doing, causes more temperature differential and is more likely to condense moisture out of the hot air inside.

Also, I have a 2'-3' crawlspace under the house. The floor for the house is 2x6s again with no insulation. What to use there? There are small vents along the foundation into the crawlspace."

Answer: Provided the gable ventilation is adequate, you can fill the 2x6 cavity with unfaced insulation. Then place additional unfaced insulation on top, placing it perpendicular to the first layer.