Insulate Under Floor: Fiberglass insulation batts or rolls are the most economical and easiest DIY choice for insulating between the floor joist in a crawl space. The U.S. Department of Energy recommends R-11 (3½”) insulation under floors in warm climates and an R-25 (6” to 8”) in cold climates.

Should I insulate between floor joists?

For optimal energy efficiency, your home should be properly insulated from the roof down to its foundation. ... In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below.

Is it worth insulating under floorboards?

Generally speaking, you only need to insulate the ground floor. If you're on an upper floor, you don't usually need to insulate your floor space. However, you should consider insulating any floors that are above unheated spaces such as garages, as you could be losing a lot of heat through those.