[Greenbuilding] [BULK] Re: Mold questions

[Kidd, Peter]

Not all foams, just those that do not use air as the blowing agent.
LTTR is the accepted measure of this effect.  Polystyrene's are quite
stable in R-value.  Polyiso for one example declines to a relatively
stable value in something like two years.  Some claim that hermetic
enclosure of foams that use lower conductivity gases allows them to
retain their higher R-values, but I'd be skeptical.  

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Lawrence
Lile
Sent: Wednesday, August 30, 2006 12:53 PM
To: Greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] [BULK] Re: Mold questions


 


>Lawrence Lile has mentioned that he caulks the stud/ sheeting
connections and the horizontal spaces between the sheeting to prevent
moisture infiltration. Another way to do this, add some insulation, and
cut down on all that caulking would be to install inuslboard with the
aluminum foil coating on it. The foam panels can cover the joints
between the sheeting if offset by, say, 12".  Being foam, the moisture
won't pass through the panels. The joints between the foam panels can be
taped over with Tuck Tape or some such.

I decided to avoid the foil faced insualtion, prefering materials that
allow some moisture transport.  Extruded foam does allow some moisture
to move (not a lot) whereas foil faced does not.  I am convinced that
the ability to dry is more important than low permeability.  

Also, I am worried about placing the foil faced on the outside of a
house, the wrong side for a vapor barrier in my area.  In addition, I
have understood that the foil faced insulations, which start out at a
really high R value, end up outgassing the blowing agent and then losing
R value over the years.  All foams have this problem, but the
polyisosyanurate has the problem to a greater degree.  This comes from a
contractor, I don't have a reference for any reasearch on this.  

The manufacturer of Extruded foam board recommends a 1/4" gap between
boards for expansion and moisture movement, with no tape cover.  Tyvek
over the top will keep air from moving through the gaps.  

Your Mileage May Vary, of course. 

--Lawrence Lile


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