Vapor Barrier Needed?


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Old 11-20-15, 07:52 AM
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Vapor Barrier Needed?

The house we bought earlier this year has a vapor barrier in the attic the way it should be. However, it looks like some remodeling was done at some point in the main bathroom and the drywall must have been removed. Along with the drywall, the vapor barrier was removed.

So, at this point I'm wondering what to do. Since the drywall is up already, if I add a vapor barrier now it would be between the studs. It's no longer possible to put one continuous sheet between the studs and the drywall from underneath like you normally would because the drywall is already in place.

So, does it make sense to just put the vapor barrier between the studs up in the attic? I realize it won't be as good of a moisture barrier compared to how a vapor barrier is normally installed. There is not much insulation above this bathroom either so another option could be to use faced insulation over the bathroom. Or, I could leave it as is and just add more insulation up there with no vapor barrier.

What would you guys recommend? Thanks!
 
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Old 11-20-15, 08:30 AM
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The best option is to use two coats of oil paint/primer in the bathroom, that will give you an equivalent vapour barrier. Also, go in the attic and use spray foam and acoustical sealant to make sure any penetrations are sealed tight. More important than that, however, is that you have a functioning bathroom fan that is properly vented to the outside, and that it is used.

Adding more insulation will do nothing to stop vapour from getting into the attic.
 
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Old 11-20-15, 09:17 AM
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Bathrooms can be a bit of a problem with all of the moisture there. Having the drywall, then VB, then framing and insulation means any moisture passing through the drywall gets trapped at the VB layer and ultimately has to dry back to the bathroom. Doing as Keith suggests keeps the majority of that moisture out of the drywall right from the start and any that gets in can dry to the attic or slowly back to the bathroom. Good attic ventilation can handle that small amount.

The other part of the problem is reducing the moisture in the bathroom. Installing a timer on the exhaust fan so it continues to run 20 minutes (adjustable) after being shut off helps to eliminate the moisture before it can become a problem. They make inexpensive switches with the delay option built in.

Bud
 
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Old 11-20-15, 12:55 PM
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Thanks for the replies!

What kind of spray foam would you recommend? I looked into the spray foam they use in new construction in the basement between joists as I want to do some of that kind of insulation as well and the kits were over $300?
 
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Old 11-20-15, 04:23 PM
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Most DIY projects will cut and fit rigid foam boards and seal them with either caulking or can foam. The idea of DIY spray foam is only desirable when the area being filled is impossible to fill with pieces of rigid. It is a nice idea, but it has been expensive right from the start.

Bud
 
 

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