I am redoing a shower, tearing off old tile, replacing green board with Durock. I need help on whether I should or should not put a plastic sheet, vapor barrier over the studs before putting in the Durock. I am in a second floor condo and I don't want any water getting behind the shower walls and dripping down into the lower unit. I have read some other posts on this topic. Some feel the Durock should "breathe" to dispense any moisture to prevent mildew for forget the plastic sheet. My worry is if my unit causes damage below- I have to pay to fix it. I want things waterproof. I read another post suggesting a 12" strip of plastic along the top of the tub area with the plastic overlapping the lip of the tub and sealed against it. That ought to be water proof and leave the Durock above the strip free to breathe. In any event, I'd welcome any opinions on the issue of a plastic vapor barrier under/behind Durock. Thanks.