insulating a house without exterior sheathing or vapor barrier
I live in Atlanta, Ga and purchased a 1-story 1200 sf, 1930s bungalow on a +/- 2' brick crawl space. It is in need of updating and repair, which I am in the middle of completeing now. I have completely gutted a bathroom and kitchen and rebuilt from the piers up. I have subfloor down but still have exposed stud walls on the interior.
When I did the interior demo work I was amazed to see that the 1x12 exterior siding was nailed directly to the studs on the wihtout any exterior sheathing or vapor barrier. My question is before I install drywall what is the best way to insulate these walls and install vapor barrier if necessary without removing all the siding?
I've looked into open cell foam but my kitchen and bath are too small of a job making it very expensive (no economy of scale) I've also heard of using closed cell foam too but reports are not good with regards to its insulation value. My gut reaction is to just add fiberglass insulation (won't absorb moisture) and then use "greenboard" or some other moisture resistant wallboard or regular wallboard with a vapor barrier installed before hanging drywall. Unfortunately removing the siding is not an option as both are in mid stream of walls and I really don't want to add that to my already long to do list.
Any advice would be greatly appreciated.