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Don Harris CSI, CCS, CCCA, AIA
Senior Member
Username: don_harris

Post Number: 231
Registered: 03-2003


Posted on Thursday, September 17, 2009 - 02:30 pm:   Edit PostDelete PostPrint Post

2006 IECC 502.2.3 states:

"Above-grade walls. The minimum thermal resistance R-value) of the insulating material(s) installed in the wall cavity between the framing members and continuously on the walls shall be as specified in Table 502.2(1)..."

Based on Climate Zone 4A, metal framed wall, R-13 is required.

I am confused with the wording of the code when it says, "The minimum thermal resistance (R-value) of the insulating material(s) installed in the wall cavity between the framing members..."

We know that a typical 6" CFMF wall, brick veneer and R-19 insulation is in reality an R-7 or R-8. So, if all the code requires is R-13 between the framing members the actual R value will certainly be below R-7. I thought the whole idea of the Energy Code was to save energy. Why is the requirement so lax? What am I misreading? What am I missing? Why doesn't the code require an actual calculated R value?
Ronald L. Geren, AIA, CSI, CCS, CCCA, SCIP
Senior Member
Username: specman

Post Number: 798
Registered: 03-2003


Posted on Thursday, September 17, 2009 - 03:11 pm:   Edit PostDelete PostPrint Post

You need to look at Section 502.1.1. It states that the "building thermal envelope" shall meet the requirements of Tables 502.2(1) and 502.3.

Since the definition of "building thermal envelope" describes the assemblies that enclose conditioned space, then entire assembly must have an R-value of 13. Section 502.2.3 only stipulates that the insulating materials can't have an R-value less than that indicated in the Table.

At least that is how I interpret it. FYI, the 2009 IECC doesn't change that much from the 2006.
Ron Geren, AIA, CSI, CCS, CCCA, SCIP
www.specsandcodes.com
David Stutzman
Senior Member
Username: david_stutzman

Post Number: 56
Registered: 07-2002
Posted on Sunday, September 20, 2009 - 02:19 pm:   Edit PostDelete PostPrint Post

502.2.3 indicates that the values shown in Table 5.2.2(1) are the minimum values for the insulation materials, not the assembly. For thermal calculations, though, the effective R-value given by ASHRAE 90.1 should be used. This will reduce the insulation rated R-value by 55-65% depending on stud size and spacing. So that R13 insulation may be as little as R6 effective value. Previously, the full R13 was typically used for energy calculations, so the codes are having an effect on improving energy performance.

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