Where is a vapor barrier required?


Old 07-11-14, 04:46 AM
Thread Starter
Join Date: Jul 2014
Location: USA
Posts: 1
Where is a vapor barrier required?

I've been doing some DIY work around my new house and I noticed that behind the exterior-facing drywall in my bathrooms there is a vapor barrier. It is the only room on the main level that has it though. As far as I can tell, the bathrooms are the only rooms in the house with vapor barriers behind the exterior-facing drywall.

Is this normal? And if not, how much of a problem could it be? I had thought normally they are put on all exterior walls.

This is all on the main floor, not in a basement and there is no 2nd story. The house was built in 1979 and I reside in Michigan if that helps.

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Old 07-11-14, 05:54 AM
Join Date: Oct 2008
Location: New England
Posts: 9,997
Strange to see that on a 79 home, but becoming more common in newer construction. The concept of a (plastic) vapor barrier was oversold years ago and has now given way to the term "vapor diffusion retarders" (VDR), link below.

In some cases a VDR might be more necessary in a bathroom, but new thinking there is to put a delayed off timer (special switch) so the exhaust fan gets rid of most of the excess moisture. So the VB in behind the drywall in the bathroom is doing no harm and the lack of same through the rest of the house is covered by the paint and perhaps a kraft facing on your insulation. Another link.

BTW, the number one issue you should address with a 79 home would be air leakage.

Vapor Barriers or Vapor Diffusion Retarders | Department of Energy
Vapor Retarders and Vapor Barriers | GreenBuildingAdvisor.com


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