[Strawbale] Vapor Barrier (was: Pressure-treated Wood Foundations ( PWF) )

[Shody Ryon]

--- Speireag Alden <speireag at gmail.com> wrote:

> Sgrìobh Shody Ryon:
> 
> >I don't know. Did you say that installing a vapor
> >barrier interior to the insulation would prevent
> >condensation in the insulation space?
> 
>      Yes.  Properly sealed, it will.  But vapor
> barrier isn't the same 
> as Tyvek, which is what most people mean when they
> say "house wrap". 
> Tyvek is intentionally vapor permeable, so that it
> sheds any rain 
> which gets through the siding, but lets vapor out of
> the wall, so 
> that by the time the wall cools enough to permit
> condensation, it's 
> dried out and there won't be any condensation to
> worry about.
> 
>      A vapor barrier is simply polyethylene plastic,
> usually 4-mil or 
> 6-mil poly.  In a cold climate, you put it to the
> interior of most or 
> all of the insulation.  That way the warm,
> moisture-laden air on the 
> inside of the building can't get into the wall in
> order to cool off 
> and dump its load of water.
> 
> >I thought
> >that some SB builder on this list do not use
> membranes
> >and plaster directly on both the int and ext of the
> >SBs themselves.
> 
>      That's true.  That's because a wet-applied
> plaster, done 
> properly, can do a pretty good job of air-sealing a
> wall, and so no 
> plastic membrane is necessary.  Though you still
> need to seal at 
> outlets and where the plaster butts up against wood
> and window 
> framing and such.
> 
> >If that is the case, I wonder if I can build a wood
> >frame house with no membrane and expect superior
> >results.
> 
>      Only if you use wet-applied plaster and seal
> all the openings.
> 
>      It's often possible to violate standard
> practices, but you should 
> only do it if you understand thoroughly what you are
> doing.  They 
> usually standard for a reason.
> 
> -Speireag.
In California there was a process of installing a "one
hour fire wall", used to isolate hi risk areas such as
an attached garage from the living space made from
5/8" gypsum board that was "fire taped", meaning it
had at least one coat of joint compound on it. I alway
thought if it sealed fire that it might seal air to
some degree, if care was taken around penetrations
esepcially elec boxes, inside and out of the box. In
the states there was trouble caused by nonbreathable
vapor barriers and I thought those were no longer
used, for about the last 20 years. All the gypsum
board taping I have seen has been high quality in
terms of air seal accept for plumbing and elec
penitrations, which never sealed inside the elec
boxes. This is from years ago and mild climates.
> -- 
> A wise man will make haste to forgive, because he
> knows the true 
> value of time, and will not suffer it to pass away
> in unnecessary 
> pain.
> --Samuel Johnson, lexicographer (1709-1784)
> 



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