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Air barrier around shower mixing valve

slader99 | Posted in General Questions on

Any ideas on recommended detailing around a shower mixing valve?

My primary air barrier is sheet material on dry side of wall (membrain). 2X6 roxul insulation with sheathing and then another 1.5″ of roxul comfort board on the exterior.

I’ve spent quite a bit of time caulking seams at tops and bottoms of stud bays, sealing up all possible holes in my sheet air barrier but now I’m scratching my head on the shower mixing valve detail. Insulation and vapor barrier is in…



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  1. GBA Editor
    Martin Holladay | | #1

    My advice is to stop worrying. Repair the MemBrain around the valve stem as best you can with a high-quality European tape, leaving enough room for the valve stem to rotate.

    Then when you install your escutcheon, use a small amount of caulk or plumber's putty at the perimeter of the escutcheon.

  2. Expert Member

    The valves are designed to keep water out of the wall. They do a good job of keeping air out too.

  3. GBA Editor
    Martin Holladay | | #3

    One more point: No one should ever install any plumbing in an exterior wall!

  4. Expert Member

    That's pretty big interdiction. Don't you think that in the case of a deep wall, where all the insulation can be located on the exterior side of the water lines that it can't be done effectively?

  5. GBA Editor
    Martin Holladay | | #5

    If you are designing a wall with all of the insulation on the exterior side of the water lines, then I strongly recommend that you install the air barrier on the exterior side of the water lines, too.

    If Colin were to follow that advice, he wouldn't be facing his current dilemma (the situation with a shower mixing valve that penetrates his air barrier).

    That said, I'll agree that I'm talking like a Vermonter. In Vermont, you really don't want any plumbing in your exterior wall. But you won't have problems with that approach in San Diego or Miami. And even in Atlanta, you can get probably away with it -- but there were a lot of frozen pipes in Atlanta over the last two winters.

  6. slader99 | | #6

    I wanted to keep the shower plumbing off the exterior wall but the boss over-ruled me. I did win a couple small battles; we only have a single pot-light in the upstairs ceiling. I'm not so worried about R value with 2X6 insulation and the full 1.5 exterior insulation in a 4c zone.

    More worried that an upstairs shower stall would be the worst place for warm moisture laden air to deposit its water on the way out of the house.

    There's conflicting advice about caulking all the way around an escutcheon (leave a small gap at the bottom for moisture to drain back into the shower). This advise is probably more geared towards the installation on an inside wall where vapor/air sealing is a non-issue? Sealing all the way around is probably in my best interest given my circumstances?

    I've already sealed the vapor/air barrier to the outside plastic rectangle of the mixing valve housing. I'll now try and do my best to seal the inside of the plastic housing the the outside of the mixing valve body.

    Thanks for the input guys, have a great day!


  7. Expert Member

    I wasn't thinking about the air barrier - which shows i'm a bit thick as that's what the question is about.

  8. Aquatiteman | | #8

    Hi there, I have just become a member so my reply may be too late....however I have developed a range of products that do exactly this....sealing the penetration in the wall lining around your shower mixer and or tap is vital to the integrity of the waterproofing of a wet area. Have a look at for an overview of the Wetwall Caddy how it is installed and how it actually performs. I would love to hear from anybody who may find this product beneficial to their business. Thanks

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