Vapor barrier

[Danj6767]

Have all
My first post here I've been a long time lurker.

I'm building workshop next to house, 32X20 I've passed structure and electric inspection. I'm not doing insulation now faced on walls and mixed faced and unfaced on ceiling. I've looked around but can't seem to find the information I'm looking for. What is the general consensus on vapor barrier on walls and ceiling? I'm at the point I gotta decide the ceiling and walls will have 1/2 sanded plywood..

Looking forward to to your input...

 

[bullnerd]

Whats your location?

 

[Danj6767]

Central Iowa...

 

[Marctrees]

Danj - in your climate the VB is placed immediately behind the interior wall finish, in this case the 1/2" ply.

If alot of your ceiling does not have at least the kraft paper, you should put 4 mil poly up immediately behind your 1/2" ply.

Vapor barrier thinking is morphing in recent years, but most experts still agree on what I said in YOUR geo area and NORTH of there.

In rough terms, starting maybe ?500? miles South of you, the newer thinking is generally NO VB.

And, in the southern states, the VB is placed on the OUTSIDE of the insulation.

This is very summarized in general.... but in YOUR area and N of you it goes on the INSIDE side of the insul.

Marc

https://www.iccsafe.org/wp-content/uploads/proclamations/TN06-Vapor-Retarders_pdf.pdf

Below is written by THE guy that is considered the most knowledgeable on this subject.


https://www.buildingscience.com/sit...te/pdf/RR-0410_Vapor_Barriers_Wall_Design.pdf

 

[yeldogt]

I would not use plastic ... it's a class 1. Traps moisture ...

Read the studies ... be aware of the dates .. some are old.

What do you have as outside sheathing?

Your post is a little confusing on what you are actually doing ...