I need to insulate under a floor that has hydronic radiant heat. I am going to use fiberglass batts between the joists of the floor, with the kraft vapor barrier upward (toward the warmer area). The area under the joists is an unvented crawl space.
I have a good bit of R-30 batts, 10 1/4 x 16, left over from another project. I would like to use it in the spaces, which are a true 6 inches deep (combination of old full-sized lumber and engineered beams). I could simply strip off about 4 inches of the fiberglass, but I hate handling that stuff any more than necessary. If I compress the batts into the 6 inch space, am I significantly compromising the R value? I realize it won't be R-30, but will it be less than R-19, which is the common value for 6 inch insulation?