Big Green: Effective R-value of rigid insulation with z-furring

[Christopher Sweetnam-Holmes]

FYI-  We've done a Multi-Family with a similar approach to what Meg has
described- however we Used a nice product from James Hardie called AP Foil
Faced PolyIso insulation.  

The assembly was-  6" metal stud, 4.5" AP Foil Faced PolyIso insulation.
With taped joints, Vertical Metal hat Furring, - The poly iso was anchored
using long 5.5" Screws through the metal furring, insulation and into the
studs.  The hardie planks are mounted on furring.

The foil facing in this assembly works as an a vapour barrier.  We've loaded
all the insulation on the exterior and found that it functions optimally
this way. And while it seems at first counter-intuitive to have the vapour
barrier on the outside,- it does in fact work-
I can elaborate if anyone is interested.

Cheers,


Christopher Sweetnam-Holmes, 
B.I'ntl. Bus., B.E.D.S. (Arch), 
LEED Accredited Professional
---
EcoCite Developments
innovative.urban.green
innovateur.urbain.vert
www.ecocite.ca
 
514.524.0191
m:613.263.0801 
f:514.523.0436

 

-----Original Message-----
From: biggreen-bounces at lists.biggreen.org
[mailto:biggreen-bounces at lists.biggreen.org] On Behalf Of Meg Needle
Sent: January 16, 2008 5:49 PM
To: Kristian Kicinski; biggreen at lists.biggreen.org
Subject: RE: Big Green: Effective R-value of rigid insulation with z-furring

We usually design similar walls with the Densglas between the metal studs
and the rigid insulation.  You can still dampproof the Densglass and then
install the insulation with small button fasteners instead of the z-strips.
We usually have masonry veneer so the masonry anchors can be the type of
system to secure the insulation to the sheathing.  However, in your case,
the rigid insulation can be speced t&g so with the Densglas backing you can
probably find a screw type button fastener for the insulation.  We have had
good luck fastening the Hardi through the foam to the studs or possibly even
the Densdeck with the right screw fasteners and spacing.  By eliminating the
z-channels, you'll minimize your thermal bridging and, most likely be able
to use the full R-value of the foam.  You'll need to make sure your dew
point is not in the stud cavity though.  With some evaluation, this might
prove a good alternate.
 
Meg
Lord Aeck Sargent Architecture
 

________________________________

From: biggreen-bounces at lists.biggreen.org on behalf of Kristian Kicinski
Sent: Tue 1/8/2008 1:24 PM
To: biggreen at lists.biggreen.org
Subject: Big Green: Effective R-value of rigid insulation with z-furring


Hello BigGreen:
I am looking for information on how to calculate the effective r-value of
rigid insulation when it is installed between metal z-furring channels.
 
Our wall assembly is as follows:
6" metal studs with R-21 fiberglass batts 1" vertical z-furring attached at
each stud
R-5 polyiso rigid insulation installed between z-furring 1/2" Exterior
gypsum sheathing (dens-glass gold) Fluid-applied air barrier (Henry's)
Cement board siding (Hardi)
 
During design we intended the rigid to be installed over the studs with no
z-furring in order to prevent thermal bridging in the assembly, and for the
gypsum sheathing to then be fastened through the rigid.  However, the
contractor has already begun installing the z-channels, so now I am trying
to determine the effect this will have on our energy performance, since the
z-channels create a thermal bridge through all the insulation.
 
Thanks,
Kristian Kicinski
 

Kristian Kicinski AIA
LEED Accredited Professional

Bassetti Architects
71 Columbia St. #500 | Seattle, WA 98104 P (206)340-9500 | F (206)340-9519

kkicinski at bassettiarch.com <mailto:kkicinski at bassettiarch.com> 

 

 
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