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General => General Forum => Topic started by: CabinNick on September 08, 2020, 05:57:49 PM

Title: Vapor Barrier??
Post by: CabinNick on September 08, 2020, 05:57:49 PM
I am getting read to start installing paneling on my interior walls, but I am a bit confused on whether or not I need to install a vapor barrier  over the insulation. 

A bit of background - I am building in Northeast Oregon, seasonal cabin that will primarily be used in the Spring through Fall, but occasional trips in the Winter.  Cabin is heated entirely by wood stove and water will be winterized.  Cabin is on an insulated crawl space and roof is vented. No AC, dry hot summers, cold dry winters.  Exterior of the cabin is 1" pine board and batten, with house wrap, and then 7/16" OSB.  2x6 studs that will be insulated with R-21 batts and covered in 1x6 T&G knotty pine. 

Question is, whether or not I need to install a plastic vapor barrier on my walls below the knotty pine paneling?  Energy conservation is not an issue, since we are off grid, entirely wood heat and surrounded by millions of acres of firewood.  I thought by code I needed to have a vapor barrier; building inspector is telling me no but insulation contractor is recommending one.  Thoughts? 

P.S. On my to do list is to update my cabin build thread; has been a busy summer but have gotten a lot done and am finally ready to start finishing work. 
Title: Re: Vapor Barrier??
Post by: akwoodchuck on September 08, 2020, 07:08:53 PM
I've always said, if you have a big ol' woodstove cranking (and preferably a window or two cracked open), you definitely don't need a vapor barrier...however I will qualify that by saying your air barrier (Tyvek) needs to be tighter than a duck's butthole....it's air leakage/movement that transfers 99.9% of moisture into wall/ceiling assemblies, vapor diffusion does the rest....
Title: Re: Vapor Barrier??
Post by: MountainDon on September 09, 2020, 10:27:54 AM
According to this map (https://www.certainteed.com/insulation/resources/do-i-need-vapor-barrier/) it appears you should use an interior wall vapor barrier.   This building science article (https://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers) agrees and has more info than you might want.  Near the end of the article it specifies that where you are should have a class three or better vapor barrier.

I think where you are, in your wood heat oly situation you could use one or forgo one and not be in trouble either way.
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