We are planning on converting an attached garage to living space. To do so, I will be putting in floor joists that will not be sitting on the garage slab floor. They will be raised to meet the floor height of the rest of the home's living space. My question is this: do I need a vapor barrier between those floor joists and the current garage slab floor? The garage (and home) is 26 yrs old, if that matters. I don't notice moisture (condensation) on the floor on warm, humid days, but we have the door open most of the time. I certainly don't want moisture ruining the insulation I plan on hanging between the joists and/or creating a problem for the living space itself. If I do need a vapor barrier, I am assuming I would use a large sheet of plastic and lay on the slab floor and then up the exposed garage foundation wall (on which I will be setting the joists). Does that seem correct? Thanks for any help!

I have an old home that flexes year to year and requires re-leveling once in a while. I'm interested in spray foam insulation, but concerned that the flexing might cause the foam to split from the joists and allow air to pass through. Is this an issue? I imagine that foam insulation is designed to flex with your house, but haven't found any information about it on the net.