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RE: Vapor Barriers for Wood

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Glyn-
 
I have seen a major developer we design for typically wrap the end of the beam with continuous aluminum flashing (termite shield) and then grouting the pocket solid around the aluminum.  My concern with this is that I see the potential for moisture to condense on the surface of the metal in humid conditions since the metal flashing is in direct contact with the concrete and generally remains cool.  It would seem that this detail may draw moisture to the end of the beam at the pocket.  I know that there typically is no attachment of the beam to the wall, so the wrapped and grouted detail would seem to provide more support for lateral loads than the air gap detail.  I know this doesn't completely answer the question, but I hope it helps a little.
 

Albert J. Meyer, Jr., P.E.
Martin-Espenlaub Engineering

-----Original Message-----
From: Glyn Boone [mailto:BooneG(--nospam--at)trusjoist.com]
Sent: Wednesday, January 10, 2001 10:28 AM
To: seaint(--nospam--at)seaint.org
Subject: Vapor Barriers for Wood

When an untreated wood beam frames into a pocket in a concrete or masonry wall, the codes require some type of protection.  Typically, I have seen a treated sill with an air gap around the beam or some type of vapor barrier.
 
Does anyone have some good industry recommendations?  What is an acceptable vapor barrier (metal, builder's felt, termite shields, etc)?  What about wrapping the end of the beam in aluminum trim and leaving no air gaps?
 
Thanks,
Glyn