Vapour barrier behind bathtub

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Posted by: from Chatham
1/8/2018 at 2:10:58 PM

I am redoing by bathroom and I have already installed the bathtub. One of the ends of a tub is on an outside wall. I forgot to put the vapour barrier up before installing the tub so there is a small section behind the bathtub that I'm not going to be able to have vapour barrier. This section is only the hight and width of the a standard bathtub.

Is this going to cause a problem or should I be taking out the tub and plumbing?


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Frank from Reno Force in Princeton
Date/Time1/8/2018 at 3:11:43 PM

Hello Brian.. if not to much trouble do your best and remove the tub and install it however that being said it's a small area and won't be a issue as long as it's insulated you should be good, my first choice is to try and fix it first.

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Date/Time1/8/2018 at 3:23:08 PM

Hello, their should always be a vapor barrier on outside walls. The correct way and to insure no issues in the future it would be recommended to install prior to the bathtub installation along with appropriate tuck tape seam application.

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Date/Time1/8/2018 at 3:33:40 PM


If you can drill straw sizes holes into each area between outside studs. Fill these area's with expansion foam insulation. Available at any big box store. Be sure to fill the areas plus some above the installed vapour barrier.

The spray foam insulation will act as a vapour barrier.


James Fram

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Date/Time1/8/2018 at 3:54:00 PM

Hi there,

The general purpose of Vapour barrier is to to keep water vapour from coming into contact with your drywall and causing mold amd to act as a air barrier.Many years we built with little or no V.B without many issues. With being a small area and with open area under tub you should not have issues with mold because you will have some air penetration. If insulated properly you will be ok.. ideally it should have been done but I don't feel it necessary for you need to remove the tub. That being said..the newer and subsequently, more air tight the home the more important it becomes to maintain that standard.

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Date/Time1/8/2018 at 5:03:24 PM

Hi Brian,

Best to do it properly remove it and install the vapour barrier it could be a very expensive mistake for you. That is my best advise better to be safe than sorry.


Darren Smith

Allure Construction & Restorations Inc

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Date/Time1/8/2018 at 7:05:49 PM

Hi Brian,

I know is sucks, but I highly recommend you remove the tub and install the vapour barrier. Insulation is part of a system and does very little for you with the vapour barrier.

Hope this helps.


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Date/Time1/8/2018 at 9:13:39 PM

Yes 6 mil Vapor Barrier is important to be sealed on all exterior walls and ceilings from floor to ceiling and use duct tape for joints and caulking at the base. If it's not a big deal I would recommend moving the tub and installing a vapor barrier properly or forever have a cold draft

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Ken from Ottawa Bathrooms in Ottawa
Date/Time1/9/2018 at 11:08:56 AM

I would recommend removal and properly redoing as well...if you don't, you could have issues with freezing on that wall...all it takes is a bit of cold draft..l.then you will be redoing entire project...

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Date/Time1/10/2018 at 10:00:40 PM

The vapour barrier should be sealed all the way on all sides however you can just move on if it's too much work would be involved!

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