Re: [GBlist] vapor barrier

[Sacie H Lambertson <dlambert@grasshoppernet.com>]

Hmm,
	Still a bit of a conundrum. IF if were possible to really seal the EPS,
then I would leave it at that, and let it be the vapor barrier, but my
experience to date is that this is not entirely practical.  If I were
applying the foam adhesive between each 2' width of the EPS blocks then I
would be assured it would be OK, but my diligent crew, regardless of my
exhortations, will not get it all sealed, therefore I feel I may need a
separate barrier.   (I've just spend hours foaming between sections of the
EPS walls where they supposed to be already sealed).  Several responses
have indicated that felt is not a vapor barrier however but kraft paper is,
so maybe I'll go that route.   As an aside, I'm not all that concerned
about protection of the decking, since our summer weather produces
relatively little rain and we'll be doing the entire roof in sections (and
I have some big tarps).
	And because the metal roofing is attached to the roof via straps of metal,
there won't be the traditional felt on top of the EPS; it would be
redundant to place it both under and over the insulation.  On another
project, when I placed SIPs (which are EPS sandwiched between OSB) on a
roof I placed felt on top (to protect the OSB) and taped the seams of the
OSB underneath with Tyvek-type tape to make sure warm moist air did not
leak from the interior in the winter.  I think a metal roof is particularly
susceptable to too much trapped moisture.
	Thanks to all for your responses, most appreciated.   Sacie Lambertson

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