Vapor barrier floor?

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Old 11-21-19, 05:02 AM
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Vapor barrier floor?

I thought the idea with a vapor barrier was to literally encase the room in barrier to stop moisture but I never see any plastic under the flooring taped to the wall barrier.
doesn't this allow moisture in through the flooring and into the cavities and walls?
 
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Old 11-21-19, 07:33 AM
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You could use a vapor barrier that way but water could neither move into or out of the room that way. They are typically used to stop water from moving through a surface where it would be normally expected to do so, like a wall exposed to outside air.
 
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Old 11-21-19, 10:44 AM
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I got the impression that vapor barriers were often not applied in the joist cavities and therefore moisture could always get in there.
should I be putting barrier against the insulation even in the cavity area against the wall?
 
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Old 11-21-19, 11:12 AM
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First, you need to make sure you are code compliant, so I would start with the local AHJ. From what I know, Canada tends to be a little behind current thought of vapor barriers not being necessary so you may have to use one regardless.
 
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Old 11-21-19, 12:36 PM
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The thinking here is due to climate. Lots of potential for condensation especially on solid wood wall houses.
 
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Old 11-21-19, 04:48 PM
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Same question though...
what use is a vapor barrier on a wall if no-one puts barriers on the floor or in the joist cavities (especially when only partly renovating).
Seems like a huge gap in the house for moisture to enter.
 
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Old 11-21-19, 05:56 PM
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Concrete slabs are considered sufficient. If a crawlspace with a dirt floor, then a vapor barrier is recommended.
 
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Old 11-21-19, 06:45 PM
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I mean room vapor barriers. Eg bathrooms
 
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Old 11-22-19, 02:27 AM
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Canada tends to be a little behind current thought of vapor barriers not being necessary
You want to be careful if considering vapor BARRIERS, unless you have the ability to monitor and control moisture you could be creating a big problem with a sealed environment!
 
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Old 11-22-19, 06:00 AM
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I thought the idea was to prevent condensation on cold outside walls especially solid wood ones
 
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Old 11-22-19, 06:27 AM
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The idea of a vapor barrier is to keep your insulation dry.
Fiberglass lose R value when it becomes wet and takes forever to dry out.
Also it helps reduce drafts through the wall.
 
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