Hi! I know that we have to describe the construction of the opaque envelope and reference the 90.1 Appendix A table in the minimum energy performance calculation. Can I use the Appendix JA4 in California Building Energy Efficiency Standard (Title 24) instead of 90.1? Title 24 uses calculation method from ASHRAE Fundamental Handbook to calculate U-values so I wonder if it is acceptable for LEED documentation.
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5912 thumbs up
February 13, 2024 - 12:27 pm
I don't see why not. As long as the Title 24 appendix accounts for the derating of whole assemblies due to structural members it should be fine. If you compare the results from the two do you get similar results? I would assume so but it couldn't hurt to double check.
Jamy Bacchus
Associate PrincipalME Engineers
26 thumbs up
February 13, 2024 - 9:16 pm
The tables aren't identical. My limited use of both is that the CEC JA tables are less optimisitic of the assembly U factors. Some of the discrepancies might be due to assembly construction differences and/or material assumptions. My hunch if one were to cherrypick values they'd use 90.1 Appendix A.
Note: the original post included a link to the prior version of Title 24 rather than the current version. But T24-2019 is still newer than 90.1-2010.
We're in this weird area where newer codes like 90.1-2022 has Table A10.1 Thermal Bridging Psi-Factors and Chi-Factors for Thermal Bridges or BC Hydro's Building Envelope Thermal Bridging Guide prepared by Morrison Hershfield to tell you that 90.1-2010's Appendix A's tables didn't capture as many examples or tell designers how to derate for other types of bridging. If LEED v5 references 90.1-2019, then it too will also be a touch behind these latest methods, but it might have language specifically addressing this. Keen reviewers should take note when the draft is released.
The v4 Energy Update didn't touch this, so we'll have to keep allowing 90.1-2010 Appendix A values to be used even if we know better.