Steel Framed Wall for baseline case

LEEDuser Basic Member

0 thumbs up

November 4, 2021

Hi folks,

I am creating wall assembly layers for baseline case. I am using DC energy code not LEED. But thought of taking help from the wisdom of this forum.

As per code, I trying to create assembly layers to get U-0.058. The materials per code are Stucco(R-0.08), two layers of Gypsum board (R-0.56+R-0.56), insulation (R-15+R-8 c.i.), interior air layer (R-0.68). The effective cavity insulation R-value for R-15 is 6.4 as per table, combining all layers, I am getting R-16.28 or U-0.061.

That is, R-total=0.08+0.56+6.4+8+0.56+0.68=16.28; U-total=0.061

Could somebody help me on this? how do I get U-0.058 using these layers? Kindly enlighten me if I am missing something.

Thanks,

John

Post a reply

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Fri, 11/05/2021 - 14:27

Depending upon the software you are using there are usually more than one option for how you enter the wall U-values. Instead of the layer-by-layer method is it possible to simply enter a U-value for the assembly as a whole?

Jamy Bacchus

Associate Principal

ME Engineers

LEEDuser Premium Member

29 thumbs up

Sat, 11/13/2021 - 07:27

are you including the exterior air film? i don't see it in your calc. see 90.1's Appendix A A9.4.1 Air Films.
what's your framing? is it wood or metal stud? what spacing and what depth?

You can look at the 90.1 lookup tables in Appendix A to see if your assembly should be 0.058, but for building walls you can do this within the software either by layers or usually a simplified approach.

you can also check out other tools and resources:

CA Title 24 Joint Appendices (JA4) JA4.1.2.1 Determining R-value and U-factor of Construction Assemblies
Applied Building Technology Group’s online tool
ekotrope’s online tool
ORNL’s online tool

none of these will deal with the thermal bridging calcs now part of the DC code. at some point you might want this great free guide:
Building Envelope Thermal Bridging Guide (BETB) v1.4