Insulating attic knee walls
Our old house has a finished attic room that is not insulated. We are embarking on insulating the knee walls and the small bit of the ceiling we have access too from the rest of the unfinished attic. Our access to the back side of the knee walls is pretty good.
I know I need to seal the air gap between the floor joists. For that I'm planning to cut some rigid foam insulation to rough size and then seal it in place with some expanding foam.
What I can't figure out how to do is get the fiberglass batts to stay in the stud bays. Should I minimally staple them in place and then cover it all with more rigid foam insulation? Or just space some 1x2s across the studs? What I don't want happening is that in 3 years (or whenever) the fiberglass batts have slumped down into the bottom of the stud bays.
I also can't figure out if I should be using a vapor barrier. I live in the Los Angeles area, as I know that makes a difference. The best guess I have so far is that a vapor barrier is unnecessary in my area, and if I use one it should be next to they drywall.
I also realize I asked quite a few questions here. Thanks for any input!