[SlowSL]

Hey guys, I hate to even post this as it's been discussed a million times all over the internet, but the answer still remains open, with lots of different arguments and ideas as to why it should be done a certain way, and no clear cut answer that I could find.

I'm remodeling my bathroom, and specifically, a new bathtub/shower is going in, and I'm installing tile in the surround. I plan to use either Redgard or Kerdi for the waterproofing on top of cement board. My question is this, one side of the tub is on an exterior wall. My exterior walls have insulation without paper, and some type of plastic as the vapor barrier covering the studs/wall on the interior side (Home build in 1970). People suggest not using a vapor barrier if you are waterproofing on the shower side of the cement board, because the cement board would be sandwiched and there would be nowhere for the moisture to escape IF it was to get past the water barrier. but then people argue that in their case it did not meet code unless a vapor barrier was installed on exterior walls. I've even read people suggest keeping the vapor barrier, but adding furring strips to the exterior studs to keep a 1/4" air gap between the vapor barrier and cement board. I'm ready to finish this project, and I have yet to find a straight answer. Could someone please help?

 

[NotYerUncleBob2]

There's no "straight answer" because it depends. Canada I think requires a polyethylene vapor barrier no matter what (even though it's counterproductive in many scenarios) while depending on your climate zone in the US it will either help or hurt in the long run.
You could use a "smart" vapor retarder that blocks bulk movement of moisture while opening when the conditions are right to allow drying. Not sure in your scenario, but it might be a solution.

 

[SlowSL]

There's no "straight answer" because it depends. Canada I think requires a polyethylene vapor barrier no matter what (even though it's counterproductive in many scenarios) while depending on your climate zone in the US it will either help or hurt in the long run.
You could use a "smart" vapor retarder that blocks bulk movement of moisture while opening when the conditions are right to allow drying. Not sure in your scenario, but it might be a solution.

Thanks,
I've decided I'm leaving the vapor barrier and making sure I do a good job waterproofing the surround. There was no sign of moisture in the area after all these years, so hoping it stays that way after the remodel.