[Greenbuilding] [BULK] Re: [BULK] Re: Mold questions

[Lawrence Lile]

You can make a really interesting insulation detail, which works best in
hot climates, by installing layers of foil faced material with air gaps.
Turns out a 1/4" air gap with two faces of shiny material is a really
effective insulator.  Can't remember the actual numbers, but it is way
more than the R1 you'd get for a normal still air layer, and it works
better as the temperature goes up.  Doesn't work any better than a
normal air gap at low temperatures.  You'd probably want to seal it top
and bottom lest it become a chimney, and the bottom seal should allow
moisture to seep out, so caulking is out.  

--Lawrence Lile

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Chris
Green
Sent: Wednesday, August 30, 2006 2:15 PM
To: Greenbuilding at listserv.repp.org
Subject: [BULK] Re: [Greenbuilding] [BULK] Re: Mold questions
Importance: Low

Lawrence Lile wrote:
> 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.
I've recently heard this too. In fact, the buyer of the house I'm
working on mentioned it. And he's an insulation contractor. I think that
we are using the styrofoam and foil Insulboard because it has the foil
and reflects the heat back into the house and wall cavities. I assume
this will help create a warmer and drier stud cavity, but since this is
a desert area (about 5" of precip  a year) the type of moisture problems
found in, say, Oregon and the Olympic Peninsula/ Puget Sound area aren't
a problem.
> The manufacturer of Extruded foam board recommends a 1/4" gap between 
> boards for expansion and moisture movement, with no tape cover.
I wasn't aware of that. Thanks for mentioning it. I'll scratch the
taping idea off the list of notions... :-)

Cheers,

Chris Green.

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