Insulation under crawl space
Use R-39 fiberglass batt insulation if you can. Put the Kraft-side UP, towards the 'heated' floor. NOT the other way around.
RE: How to keep it from falling down - There are a few ways. First, do your best to get it to 'fit' in the joist-bays evenly. Don't stuff too hard. Do you best to get the Kraft up to and touching the bottom of the sub-floor. THen, you can staple or tack up chicken wire. What I did, instead, was run nylon string in a zig-zag pattern and wrapping it around each nail as I went. I didn't use staples but, instead, I used roofing nails. The 1" ones. The pattern was about 12" apart from the preceeding wrap. You don't want any 'gaps' in the 'web' that are larger than that because the insulation may fall through.
You didn't mention anything about a crawspace or what. Is his home a mobile home? ANd where does he live? This would help w/my answer.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!
If it's a basement, a dehumidifier might be worthwhile.
[This message has been edited by rpxlpx (edited February 26, 2002).]