I have a 1920's house with knob and tube, Zero insulation, and flooring nailed down in the crawl space behind the knee-wall in my half story. I would like to run with the easy solution for now and just roll fiberglass batts out over the floor, two layers perpendicular to each other. My question is about facing:

Since I would be leaving a 6 inch air gap, between the ceiling and the attic floor, will I cause damage with a facing side down on the attic floor? Or do I need a vapor barrier?

Basically, should I have one layer of batts with the facing down? Then another unfaced on top running perpendicular? Or is the uninsulated air gap going to cause condensation? Seattle WA so this is winter consideration only, no AC.