Need fiberglass insulation help
I need to insulate the ceiling of my unfinished basement, which also contains a pain in the butt crawl space. The space between the beams ranges from 14"-17" (didn't measure every beam space, just here and there). My beams are 8" deep.
I'm confused that the only insulation I've found by calling around and going to the box home stores is either 16" or 23" wide. Does that mean the insulation itself is that wide, or do those measurements include a few inches for the flaps on the facing? I'm also confused people want to know the size from center of beam to center of beam. Why? The insulation has to fit between the beams and the paper backing will be face up, toward the ceiling. So what's the deal with needing to know center of beam to center of beam?
Would I be better off buying the 23" wide batts and smashing them in? Otherwise, the 16" (whether the insulation itself is truely 16" wide or less) wouldn't fit my wider spaces. The flaps don't matter as I'm putting it paper side up. I'm sure I could cut them all down to about 17", but that would take a load of time (I need about 1100 sq ft). I've read it's bad to smush insulation in 'thick-wise' because it has to be allowed to expand to it's thickness, but is it also bad to smush the sides in width-wise?
What do I do? This is all new to me.