I have a friend who recently bought a house and the insulation under the house is seperating and pieces of it are hanging down all under the house. The insulators stapled strings between the joists to hold the insulation, but it just wasn’t enough. It looks to me like one would need to crawl under there and staple up some sort of mesh to hold the stuff up. That doesn’t sound like much fun. Any suggestions?
When we lived in Western Washington, the contractor stapled Tyvek under the floor insulation. He put string up first, just to hold the FG in place, then put up the tyvek. The floor was catilevered out over a hillside and really made a difference in the heating. It lasted the 10 years we lived there, don't know about it now :-(
Is this a crawlspace or piers?
What is your climate?
If a crawlspace search for information on conditioned crawlspace. Get rid of the floor insulation and insulation the foundation walls.
Up here in Alaska we use plywood. But all the houses are post and pad or piling, mnay without any skirting. I've seen similar construction in western WA. If your crawlspace is exposed to the elements I would definitely suggest that. We typically use 3/8" CDX plywood. In addition to keeping the insulation up it keeps the vermin and the wind out. If you are not exposed to the elements like this the chicken wire or Tyvek mentioned above would work fine. No the job isn't going to be pleasant. Wear long sleeves and get a helper to position the stuff. Good luck.