[Greenbuilding] Insulation Problems

[JOHN SALMEN]

The thermal bridging is pretty significant – group in Vancouver did some
modelling and based on 3” of extruded with horizontal z strips at 24”
spacing reduces the insulation effectiveness to 66% of its total with a wood
cladding due to the bridging. So your r10 does become an r6.6 if isolated
from the metal copper cladding (which would reduce the insul value more). 

 

Vertical wood battens or ½” foam strips would have the benefit of providing
a drain space behind the cladding as well as a thermal break. I think I
would also include a wrap over the foam before adding strips (as you don’t
know how good the liquid wrb is).

Alternatively you could add the proposed 1” layer as an exterior wrap (wrb)
instead of in the interior which would also bring up the value of the 2”
wrap – would still add a vertical spacer.

 

 

JOHN SALMEN ENVIRONMENTAL DESIGN

4465 UPHILL RD,. DUNCAN, B.C.  CANADA, V9L 6M7

PH 250 748 7672 FAX 250 748 7612 CELL 250 246 8541

terrain at shaw.ca

 

  _____  

From: greenbuilding-bounces at lists.bioenergylists.org
[mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Alan
Abrams
Sent: November 11, 2010 8:23 AM
To: J Messerschmidt
Cc: greenbuilding at lists.bioenergylists.org
Subject: Re: [Greenbuilding] Insulation Problems

 

building on John S's comments...

...are there some semi rigid strips of something like neoprene that could be
applied over the outside face of the z-bars, that would have sufficient
resistance to compression to support the cladding yet still provide some
thermal breakage before the cladding is attached?  this assumes that the
potential for heat loss through the bridges is so great that even the
addition of R-0.5 btwn bars and cladding would be significant.


AA



Alan Abrams
Abrams Design Build LLC
A sustainable approach to beautiful space
 <mailto:alan at abramsdesignbuild.com> alan at abramsdesignbuild.com
 <http://www.abramsdesignbuild.com> www.abramsdesignbuild.com
202-726-5894 o
202-437-8583 c
202-291-0626 f





On Thu, Nov 11, 2010 at 11:02 AM, J Messerschmidt <John at fourpointscg.com>
wrote:

Hi Thomas,

I love the suggestion of taping the seams and taping the board to z bars.
With the air leakage to the outside eliminated that would bring us a lot
closer to the r-10, and it would be a proper drainage plane.  My concerns
are, what kind of tape and how does water escape if it does get in?  2" of
xps has permeance of .55.  Will that allow vapor  to escape? What about bulk
moisture?  Behind the xps is a liquid applied membrane that probably has a
very low permeance, so it has to dry to the outside.  

 

Lastly, looking at the interior wall assembly, if the open cell foam has a
perm rating of 8, and 1" of polyiso has a perm of 2.33, this could be a well
insulated wall and will still dry to the inside.  Right?  Unless I'm missing
something, we'd end up with about an R30 wall.  I'd be very happy with that.
What do you think?  

 

 

Thanks!

 

John

 

 

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