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Re: GBlist: vapor permeability

Mike see my correction by Marc Rosenbaum - 

I too was under the assumption that icynene was a VR, since I was told that
once it is scrubbed, it looses its perm sealing abilities. I have also been
told that if a cavity is not filled completely on the first go around that
one cannot go back & fill in - it won't stick to itself.

We can debate the various merits of the material, be it green, cheap, or
recycled - but like so much of the insulation business, the thermal quality
and effectiveness is in the hands of the installer.

Anyway - the perm issue:

The 1 perm or pelow seems to be standard - I believe FHA requires a max of 1
perm on the warm side of both wall (except unfurred masonry) and ceilings
and that is the rating for kraft faced f/g batts. If you remember we used to
call it a 'vapor barrier' and it was some Canadians that taught us it was
only a 'vapour retarder' - we may all have to pop for Lstiburek's book or
get him to put it up on the web.

I'm surprised that you all don't have a ceiling VR requirement, one might
think that might be where a high amount of the mositure might get to. Maybe
out there you don't have a stack effect ... And are your f/g guys taping w/
expensive tape or caulking with messy caulk or lapping & by how much the poly ?

Frazer Dougherty                doughf@mindspring.com
North Fork Retrofit             doughf@aol.com (fallback)
website: http://www.home-performance.org


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