vapor barrier with multiple showers

We're redoing a shower in which the tiles were falling off because the drywall behind them were rotting. there was no water damage on the subfloor or the studs, but there were 3 layers of drywall between everything. We've taken out the nasty old shower pan and replaced it with swanstone, but before we hang the hardibacker, I've noticed it looks like we're supposed to have some kind of a vapor barrier behind it. As I've been researching though, it looks like having two layers of vapor barrier is a very bad thing.

I'll back up a minute. We are in a town home and have a master bathroom with no tub and another bathroom with a tub that back up to each other. The neighbors have the same deal except they are a mirror to us, so we have four bathrooms all backing up to each other. In our shower that we are redoing we have about nine inches from the back of their drywall to the front of our studs. I know they don't have any vapor barrier up right now. There is some old pink fiberglass insulation between for soundproofing I would guess. Then there is about 27 inches between our shower and our bathtub/shower drywall (which we will be redoing in the next couple of years). This area has the copper pipes coming up from the water heater downstairs and a couple other pipes. I tried to take pictures, but the area is dark and they aren't coming out will. I'll take some if my description doesn't make enough since though

So do we go ahead with a vapor barrier in each of our bathrooms (eventually)? I've heard there can be some kind of sandwich effect, but haven't seen it actually described.

edit: I should also add that we are going to tile.

Thanks!!!

 

can this thread be deleted? I put it in the wrong place, so I reposted.

 

The vapor barrier is really a moisture retarder to keep the inevitable dribble of water that could eke its way through the grout and cbu to keep from rotting your studs. It won't be the same as a double vapor barrier that you are thinking of on an insulated wall exposed to the outside. I assume you are insulating the walls due to proximity to each other. Have you considered using Roxul as an insulation? It is moisture resistant, mold resistant, fire resistant, just an all around good batt insulation that is easy to install.
Too bad the original contractor chose to use sheetrock to mount the tile on. What a duh moment!! Seems you are doing it right. Let us know if you get stumped on the way. We're here.

 

Thanks for your response!

The walls have old insulation in them that I think is there for soundproofing purposes. We were going to leave it alone mostly because its the itchy pink stuff and I have sensitive skin and didn't see any reason to mess with it...

we're debating the need for even putting up the vapor barrier because there is some room for air flow and it is really dry here (in Denver). I'm leaning towards do it, I just don't want to cause any issues with water getting trapped if/when the neighbors do the same thing.

I'm also concerned because we also only have the walls open about 6 feet high and are leaving the original drywall above that so I'm not sure about how we would do the vapor barrier. any suggestions there? also, how do you seal it around the valve?

 

I'm also a little confused about where a vapor barrier is supposed to end so the drips don't just sit on the subfloor. Does it go into the gap between the shower pan and the CB so it can somehow drain into the shower pan? Isn't there silicon there?

 

Remember this isn't a vapor barrier as such. It is a liner for your shower that will take water to the liner below. Above the shower is no problem. You won't be trapping any moisture between the walls if it is stopped before it gets there. See what I mean? Your neighbor should do the same thing. Overlay the wall barrier over the lip of your pan slightly. You can trim it as you tile it.

I allow 1/4" or so above the lip of the pan to allow all moisture to eke its way down and into the pan, and don't use silicone there. It is unconventional, but 1) I don't have ugly silicone to clean out and replace every so many years, and 2) the wall will stay dry behind the tile. Your tile can jump over the gap you leave with the cbu. You don't want the cbu to sit flush on the pan. Raise it slightly.