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

[Kristian Kicinski]

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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