I’ve noticed on several post where tar paper is referred to as a “vapor barrier”.
It had been my understanding that tar paper was a moisture barrier, blocking moisture in it’s liquid state, but it was breathable and would allow vapor, ie water vapor, to pass thru it.
Is tarpaper a true vapor barrier, the same as plastic sheeting?
thanks…st
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>> Is tarpaper a true vapor barrier, the same as plastic sheeting?
No. It's a lot more permeable than 6 mil polyethylene, but it is a lot less permeable than sheetrock, or cellulose insulation. Maybe it falls in the category of vapor retarder.
http://cebq.org/techinfo.html