So confused?!?!


  #1  
Old 06-05-13, 07:32 AM
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So confused?!?!

We are renovating a house from the 1950's in North Carolina. I had always assumed that the vapor barrier on the wall insulation should be facing the living area on the exterior walls. However after reading the buildingscience.com I'm not sure that is right. Can anyone guide me. Does the vapor barrier face outside or in? We are in zone 3 FYI

Thanks
 

Last edited by mwood2278; 06-05-13 at 07:44 AM. Reason: added info
  #2  
Old 06-05-13, 07:57 AM
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When you say facing.... Are you refering to thermal reflective barrier?
Vapor barrier is installed on the warm side of the exterior wall. It's normally the last item before your wall covering (drywall, plaster, etc).
 
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Old 06-05-13, 08:09 AM
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Oh I see what it is. I thought it was a vapor barrier attached to the insulation but I think the craft paper on it is the vapor retarder?
 
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Old 06-05-13, 11:24 AM
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Hi mwood, change is certainly confusing on the internet as old, new, and everything inbetween remains forever. The change that has occurred with vapor barriers is two fold.

One, they now prefer the term "vapor diffusion retarder" (VDR) as many materials provide different degrees of resistance to the movement of moisture vapor.
Vapor Barriers or Vapor Diffusion Retarders | Department of Energy

And two, it is now understood that vapor diffusion, moisture vapor moving through building materials, is far less of a concern than air leakage. So a well air sealed wall poses little concern.

Adding to the above, the old rule (which I grew up with) of installing the VB on the warm side of the wall runs into trouble in mixed climates, winter heating (it would go inside) and summer cooling (it would go outside). With the well insulated and air sealed walls we can build today, except for the deep south and the far north, we can omit the true vapor barrier and allow normal materials acting as vapor diffusion retarders to slow the moisture transfer, yet still allow drying of the wall. They say it better than I so here is another link. This one references several other articles as well.
Vapor Barriers Redux | GreenBuildingAdvisor.com

If you have the Kraft backed insulation in place on the inside it probably isn't going to do any harm because it still performs as a Class II VDR.

I'll let you read and see if any questions (confusion) remains.

Bud
 
  #5  
Old 06-06-13, 06:46 AM
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Thanks I think that's a little clearer.
 
 

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