It is very common to find insulation in the floor joists above your head in an unfinished basement or crawl space. Unfortunately, for homes in our area, this is not where you need insulation. I will go as far to say “it is a complete waste of money.”
As a general rule the entire envelope of your home should be insulated. If your basement, attic, or crawl space has duct work in it, then it is part of your home’s thermal envelope. Insulating the walls of the basement or crawl will increase the overall efficiency and comfort of your entire home.
Insulation, specifically fiberglass insulation, is often used in the floor joists in a basement or crawl space. If it is not in contact with the floor surface above, then it does not perform as intended. If you push the fiberglass in place then you smash the R-value out of the insulation so it does not work. If you want to insulate between floor joists, I recommend using spray foam insulation, but again, just insulate the walls.
