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I'm assuming, from what you describe, that you don't really have any
space between the metal cladding and the rigid foam or between the
rigid foam and the rubber? You don't have a real "drainage plane," in
other words, nor do you have moving air in those places, right? Still
(non-moving) air counts as a part of the R-value of the wall. If
you've got moving air between the foam and the rubber then the foam
sheathing isn't doing you any good.<br>
<br>
I am also pretty durn certain that putting rigid foam on the inside,
sandwiching open-cell foam in there, would be a very bad thing. You
need your wall to dry to the inside, and rigid foam definitely acts as
a vapor barrier. I believe <a moz-do-not-send="true"
class="moz-txt-link-abbreviated" href="http://www.buildingscience.com">www.buildingscience.com</a>
has the
permeability of different materials listed somewhere... Sounds to me
like you've got the airflow taken care of with the exterior stuff? Do
a blower door test FIRST, seal things up, then add insulation.<br>
<br>
I *think* you could do cellulose in the stud cavities instead of
open-cell foam. You should check to make sure you have enough foam on
the outside to prevent condensation on the interior face of the foam or
plywood. You need to do a... shoot... what are they called? The thing
where you figure out where that critical dew point inside the wall is.
You want the dew point somewhere inside the foam, so there's no
condensing surface. I *think* if your foam isn't thick enough and your
dew point is somewhere inside your cellulose that you have to do
open-cell foam instead? Can anyone confirm this... will condensation
occur on studs that are surrounded by dense-packed cellulose? That
seems so unlikely to me.<br>
<br>
-Kat<br>
<br>
<br>
<blockquote cite="mid:726109.26321.qm@web114615.mail.gq1.yahoo.com"
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valign="top">--- On <b>Tue, 11/9/10, J Messerschmidt <i><a
moz-do-not-send="true" class="moz-txt-link-rfc2396E"
href="mailto:John@fourpointscg.com"><John@fourpointscg.com></a></i></b>
wrote:<br>
<blockquote
style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px;"><br>
From: J Messerschmidt <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E" href="mailto:John@fourpointscg.com"><John@fourpointscg.com></a><br>
Subject: [Greenbuilding] Insulation Problems<br>
To: "Greenbuilding" <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:greenbuilding@lists.bioenergylists.org"><greenbuilding@lists.bioenergylists.org></a><br>
Date: Tuesday, November 9, 2010, 3:08 PM<br>
<br>
<div class="plainMail">Hi Listers,<br>
I have a 2 story house under construction, framed and sheathed, with no
windows yet in Queens, NY. It's a renovation only by DoB standards.
Some of the foundation is still there, otherwise it's new
construction. Don't tell anybody. No thought had been given to green
building or building science until now. The outside has been insulated
with 2" Dow styrofoam, but every 24" going up the wall is a horizontal
z clip, attached to the sheathing, where the bronze panel cladding will
be attached. Is that a clear description? So the profile from the
inside out is 2x6 wood studs, 3/4" plywood, some kind of rubber painted
onto the plywood that could serve as a vapor/air barrier, and 2"
styrofoam, cut every 2 feet going up the walls, with z clips in
between, and then the bronze siding.<br>
<br>
Can't take any of that off and start again, so I'm figuring the space
between the styrofoam and the rubber, as well as the space between the
styrofoam and the panels would have to serve as the drainage plane.
Question 1: Can I count this r-10 styrofoam as part of the whole wall
r-value?<br>
<br>
Question 2: For the inside, we are thinking of spraying open cell foam
in the wall cavities to prevent air flow and increase the r-value. If
we installed 1" rigid with no foil, behind the sheetrock, I think this
would block conductive heat loss and would not add another vapor
barrier. Do you think this would work?<br>
<br>
</div>
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