I have removed lath and plaster ceiling in cellar of our 17th century stone farmhouse (was cracking, sagging). Dining room above. Want to insulate between joists in most effective way. I know sheepswool is a favourite but I think Celotex etc are OK in these sorts of situations? My plan would be to tightly fit between joists and leave bottom of joists exposed. Do I need any sort of vapour barrier or can I rely on the foil on each side of the Celotex? There is excellent ventilation in the cellar which will be maintained.