Our house is built on a slope, so the staircase to the bottom floor is right above the crawl space (vented; climate zone 3). The staircase is carpeted, and there's no insulation underneath. I can access the underside of the staircase from the crawl space. What is the proper way to insulate a staircase from below?
Can I just use three long batts of fiberglass insulation from top to bottom of the staircase, without cutting it to the size of each step? (i.e., insulation won't be flush against the steps) Or is mineral wool better?
What would be the best way to hold it up there, so they don't fall? I don't have to put a drywall under the staircase, do I?
Should I use faced or unfaced insulation? (I live in a very high fire risk zone, and I read the paper on faced insulation can burn)
Thank you so much.