[Fuzz]

I re-did my bathroom a couple years ago. It's a house from the 50's, presumably before plastic was invented. Certainly vapour barrier anyway...Behind the poorly reno'd vinyl tub surround, layer of drywall and original weird tile board was wax paper overlapped but not taped over minimal amounts of insulation.

There was only a small mould spot at the window, but that was because the window was a bare wood frame with 2 un-edged pieces of glass. I'd suspect that it is to dry here for mould to be much of an issue, unless the area has other contributing factors. Everything else behind the mess had no signs of mould and was bone dry.