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Old 04-09-2011, 10:29 AM   #1
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Vapour Barrier In a bathroom ?


Hi folks

i'm going a little crazy hear reading up on the forums about vapour barriers in bathrooms

i would just like to know how the pro's do it...
i am going to install drywall and concrete board in a new bathroom. My plan was to install concrete board in the shower 'wet area' and green back board in the rest of the bathroom. Tile the shower area, and paint the rest. I plan to install an extractor fan in the ceiling. Do i need a 6mm plastic vapour barrier behind the whole installation of dry wall and concrete board or will this lead to moisture problems?

Also another general question on drywall not related to bathrooms
What is better behind the 6mm v.b... is it better to install paper backed insulation, or non paper backed?

thankyou all for a great forum

barry

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Old 04-09-2011, 11:46 PM   #2
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Vapour Barrier In a bathroom ?


It's always helpful to tell folks where the house is. Buildingscience.com can probably answer your question. I think you'll find that the vb is not a good idea. If you decide to use one, don't worry about the foil faced vs unfaced batts (I assume fiberglass); don't use them at all. Get better insulation. If you decide to use fg, the foil won't matter as it will be a vapor "barrier", of sorts, right next to the poly, so you won't have a double vapor barrier.

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Old 04-10-2011, 12:50 AM   #3
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Vapour Barrier In a bathroom ?


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Originally Posted by jklingel View Post
It's always helpful to tell folks where the house is. Buildingscience.com can probably answer your question. I think you'll find that the vb is not a good idea. If you decide to use one, don't worry about the foil faced vs unfaced batts (I assume fiberglass); don't use them at all. Get better insulation. If you decide to use fg, the foil won't matter as it will be a vapor "barrier", of sorts, right next to the poly, so you won't have a double vapor barrier.
The house is in the mid west indiana
Dont i need to put a 6mm v.b. in on the external facing cold walls behind the dry wall ?
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Old 04-10-2011, 01:56 AM   #4
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Vapour Barrier In a bathroom ?


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Dont i need to put a 6mm v.b. in on the external facing cold walls behind the dry wall ?
Probably not. VB's are being shied away from in most places. Search here and esp on the buildingscience.com site, or greenbuildingadvisor.com. The necessity of a VB is old information; I have one in my house, built in '80, because that is what everyone did. We are very cold, and likely one still would not hurt here. My new house won't have one when we build it next year. Air sealing is the name of the game. Vapor diffusion is a small fry in the water movement scheme. A 1" hole will let more water into a wall than what diffuses through a whole sheet of sheet rock. "No mass" on the VB, in the words of the once-great fighter who Sugar Ray defeated at least once. Check your code, and read it; don't trust an official to tell you. I suspect it says "vapor retarder of 1 perm or less". It may say something different, but apparently the 1 perm is widely adopted. It is the IRC code. That is our code here, and one place I checked on in upper Michigan. "No VB" is a spooky concept at first, but I've gotten over it in the last few years. Study, read your code, and make a call; it's your place.
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Old 04-10-2011, 05:37 AM   #5
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Vapour Barrier In a bathroom ?


I don't ever put a plastic vapor barrier in a bathroom.
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Old 04-10-2011, 08:36 AM   #6
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Vapour Barrier In a bathroom ?


is there any product that could be used as a VP but would let the outside wall in the bathroom Breath a little?
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Old 04-10-2011, 11:39 AM   #7
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Vapour Barrier In a bathroom ?


Vapor BARRIER and breathing don't mix. Vapor RETARDER and breathing do. The whole idea is to retard vapor and bar air. Google the "air tight drywall approach" (ADA), as well as "vapor retarder classes" (Class I, Class II, etc).

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