Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question

Revision history [back]

Title 24 vs 90.1 U-factors for metal frame walls

So this has been driving me nuts for a long time, and I thought I'd ping this community for feedback.

Title 24 (part 6), Reference Appendices, JA4 provides lookup tables for the performance properties of envelope construction assemblies. They are supposedly based on ASHRAE calculation methodologies. However, they tend to be significantly different from the values provided in ASHRAE 90.1's Appendix A.

For a specific example that comes up all the time, consider a 2"x6" metal stud wall, 16" on center with R-19 batt insulation in the cavity. Per 2016 T24 Appendix JA4, Table 4.3.3 - U-factor = 0.183 Per Standard 90.1-2016, Table A3.3.3.1 - U-factor = 0.109

That's a huge difference! What makes it worse is that this is the go-to wall type for 90% of the nonresidential projects I see in Southern California. However, Title 24-2016 has mandatory requirements for metal frame walls that say U-0.151 max, which means the construction assembly is "illegal." And even worse, when I'm providing energy modeling services for LEED and tell the architect the U-factor of their wall is U-0.109, and their mechanical engineer providing Title 24 modeling says "nope, U-0.183." (Although honestly, I feel like it's not being mentioned as continuous insulation is still not a thing here, even though Title 24 has essentially required it since 2014. But I digress...)

Title 24 vs 90.1 U-factors for metal frame walls

So this has been driving me nuts for a long time, and I thought I'd ping this community for feedback.

Title 24 (part 6), Reference Appendices, JA4 provides lookup tables for the performance properties of envelope construction assemblies. They are supposedly based on ASHRAE calculation methodologies. However, they tend to be significantly different from the values provided in ASHRAE 90.1's Appendix A.

For a specific example that comes up all the time, consider a 2"x6" metal stud wall, 16" on center with R-19 batt insulation in the cavity. Per 2016 T24 Appendix JA4, Table 4.3.3 - U-factor = 0.183 Per Standard 90.1-2016, Table A3.3.3.1 - U-factor = 0.109

That's a huge difference! What makes it worse is that this is the go-to wall type for 90% of the nonresidential projects I see in Southern California. However, Title 24-2016 has mandatory requirements for metal frame walls that say U-0.151 max, which means the construction assembly is "illegal." And even worse, when I'm providing energy modeling services for LEED and tell the architect the U-factor of their wall is U-0.109, and their mechanical engineer providing Title 24 modeling says "nope, U-0.183." (Although honestly, I feel like it's not being mentioned as continuous insulation is still not a thing here, even though Title 24 has essentially required it since 2014. But I digress...)

Title 24 vs 90.1 U-factors for metal frame walls

So this has been driving me nuts for a long time, and I thought I'd ping this community for feedback.

Title 24 (part 6), Reference Appendices, JA4 provides lookup tables for the performance properties of envelope construction assemblies. They are supposedly based on ASHRAE calculation methodologies. However, they tend to be significantly different from the values provided in ASHRAE 90.1's Appendix A.

For a specific example that comes up all the time, consider a 2"x6" metal stud wall, 16" on center with R-19 batt insulation in the cavity. Per 2016 T24 Appendix JA4, Table 4.3.3 - U-factor = 0.183 Per Standard 90.1-2016, Table A3.3.3.1 - U-factor = 0.109

That's a huge difference! What makes it worse is that this is the go-to wall type for 90% of the nonresidential projects I see in Southern California. However, Title 24-2016 has mandatory requirements for metal frame walls that say U-0.151 max, which means the construction assembly is "illegal." And even worse, when I'm providing energy modeling services for LEED and tell the architect the U-factor of their wall is U-0.109, and their mechanical engineer providing Title 24 modeling says "nope, U-0.183." (Although honestly, I feel like it's not being mentioned as continuous insulation is still not a thing here, even though Title 24 has essentially required it since 2014. But I digress...)