How many walls do I vapor barrier in tub alcove?

Discussion in 'Remodel Forum & Blog' started by ironspider, Jan 8, 2009.

  1. ironspider

    ironspider Member

    Greetings all,

    Got my tub shimmed and in place now in the tub alcove. I got some 6 mil vapor barrier and I am ready to put that up before I get on to the cement boarding and tiling and such.

    My question is though, do I vapor barrier all three walls of the surround (it's a right drain alcove so I have the left wall [exterior wall], back wall, and then the right wall [where the plumbing is]) or just the back and left walls?

    Oh, quick addon question, do I need to use cbu on the back side of the wall with the plumbing? or just the side that faces the tub? I'll throw in a quick terrible diagram explaining (I mean do i need to use CBU on the red line in the diagram below or just in the gold areas?):


  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Use CBU on all sides. Where there may be insulation already, so you don't end up with a vapor barrier sandwich, cut the existing vapor barrier (random slices are okay) then install a new, intact one on all three walls. Lap the vapor barrier over the tiling flange, ideally, either notch the studs or shim them so the cbu doesn't get bowed out and run that down over the lip. If you are using a larger tile, you can stop the cbu above the flange slightly. Cut the vapor barrier prior to tiling, ensuring it is still overlapping the tiling flange. The cbu should go up at least to the level of the showerhead, but can run higher if you want.

    For good tiling help, check out Lots of pros there that can answer tiling questions.
  3. frenchie

    frenchie Jack of all trades

    All three walls, but just the side facing the tub.

    BTW, make sure you get a decent seal around the plumbing fixtures, that's where most leak damage occurs.

    Your description was a bit confusing - did you add this question later? Because reading Jadnashua's response, I get the impression you hadn't posted the picture yet, when he answered.

    Anyways - looking at the drawing: yes to all the yellow, no to the red. The red side of that wall gets no vapor barrier, and does not need to be CBU, it can be drywall.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    I beg to differ...compromise the existing vapor barrier on the outside wall above the tub, and run a new one over it (you don't want two layers!), and run that one down over the tub lip just like on the other sides.

    Drywall on ANY side of a tub/shower is a lousy solution and DOES NOT meet national codes or the TCNA guidelines. Yes, that wall doesn't get anywhere near as much spray as the others, but is does get wet. The paper on drywall only needs to get wet a little and mold can start. Why risk it? CBU will not degrade even if you soak it in a tub of water...drywall gets really nasty.
Similar Threads: many walls
Forum Title Date
Remodel Forum & Blog Many Many Thanks To All Of You Aug 12, 2005
Remodel Forum & Blog What insulation for 2x4 exterior walls Oct 29, 2014
Remodel Forum & Blog Walkout basement finishing - insulating walls above and below grade Sep 9, 2014
Remodel Forum & Blog DUROCK Cement Board for Exterior Walls Dec 25, 2013
Remodel Forum & Blog Finishing Basement - Insulating Walls and Floors May 16, 2013

Share This Page