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Old 08-19-2011, 08:30 PM   #1
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Insulating wall between showers .. vapor barriers?


Hi folks,
I have two back to back bathrooms that share an interior wall. So the showers are back to back, separated by what is called a "wet wall" that housing the plumbing for these showers. I insulated this wall for the sake of some soundproofing. I used unfaced Roxul comfortbatt R25. Now my tilesetter is installing a tar paper type barrier and cement backer on these walls. This wall connects to an exterior wall.

My question is about the vapor barrier being placed by the tilesetter. This will sandwich the insulation between two barriers. I thought this might cause condensation in the insulation.

I still have access to the insulation on one side. So, I can remove the insulation in this section of the wall if there is a potential for moisture problems.

I'm located in the Northern California Bay Area.

Any thoughts would be appreciated.
Thanks.
Rick

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Old 08-19-2011, 11:56 PM   #2
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Insulating wall between showers .. vapor barriers?


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My question is about the vapor barrier being placed by the tilesetter. This will sandwich the insulation between two barriers. I thought this might cause condensation in the insulation.
You are correct.

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Old 08-20-2011, 01:23 PM   #3
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Insulating wall between showers .. vapor barriers?


Thanks for the reply. I noticed that the vapor barrier he is using is a asphalt kraft paper which is being installed in an overlap fashion.

So, to avoid any possible moisture problems, I think I'll remove the insulation in that section of the wall while it is still open.
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Old 08-20-2011, 06:53 PM   #4
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Insulating wall between showers .. vapor barriers?


Historically what I have done with back-to-back wet walls is to build a sound reducing wet wall. Too late now for you but for future reference and others.

This is done by using a minimum of 2X6 lumber (2X8 is better) for top and bottom plates. Then, the studs would be 2x4's, one group favoring one side (shower) and another group favoring the other side (other shower). The 2X's are staggered so as not to interfere with one-another from one side or the other. This way when the wallboard and plumbing is attached to the respective wall studs any sound from one shower cannot be transmitted through the wall studs to the other shower. Same goes for water travelling through the plumbing conduits.

In addition I would also use either waterproof wallboard or liquid waterproofing to waterproof the wallboard. This way no moisture can get into the wallboard and condensation is very much less likely.

Make any sense?
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Old 08-20-2011, 09:53 PM   #5
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Insulating wall between showers .. vapor barriers?


check on the permeability of what you have. felt paper is not a vapor barrier; real asphalt kraft paper may be, but you have no cold side to condense on, do you? no cold, no problem.
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Old 08-21-2011, 01:24 AM   #6
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Insulating wall between showers .. vapor barriers?


Actually, the wet wall was constructed just as Bud described. And the walls are being covered with kraft asphalt paper and cement backer board which will be further waterproofed with Hydroban.

There won't be much temp difference in the bathrooms. I don't think there will be a situation like an exterior wall in which there is colder temps on the outside and warmer temp on the inside. So, I agree, I don't think there would be a problem.

I spoke with my tile contractor and he advised that he has been using this system on interior walls, containing insulation, for many years without a problem. So for now, I feel it is ok to leave the insulation in the wall and proceed with the job.
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Old 08-21-2011, 12:04 PM   #7
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And the walls are being covered with kraft asphalt paper and cement backer board which will be further waterproofed with Hydroban.
Technically, there's the error right there.
The industry recommendation is to not do both. That is what can hold moisture in the cement board if it should accumulate for whatever the reason. One or the other is okay.

The conduits still have the ability to condensate.

You do whatever you think is best.


Quote:
I spoke with my tile contractor and he advised that he has been using this system on interior walls, containing insulation, for many years without a problem.
Well of course he has. I don't know of any contractor that would discuss his past failures with a new client. He could easily upgrade his knowledge and get in tune with industry recommendations if he wanted to.

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