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Fellow Modelers who have working in Massachusetts or with the newer codes with envelope thermal bridging requirements; I am seeking guidance about how you’ve gotten nearly any envelope to work. Accounting for derating factors is taking assemblies that would normally be good or high performance and making them drastically worse in calculated performance.

For example, within the Massachusetts Appendix A example calculation: MA Example Wall Starts Clearfield: U_assembly – 0.045 / R_assembly -22.2 Adding Linear Thermal Bridge – ONLY – Adds U-0.15 Clear field + Linear: U_assembly – 0.19 / R_assembly-5.2 Continuing to add the other derating factors Final Assembly U_assembly-0.25 / R-4

That’s an ~80% reduction in thermal performance(?!?!?!). Even adding CI to an assembly, the derate methodology compounds to make nearly any assembly nearly impractical.

To add insult to injury the Baseline Assemblies do not have this same derating method – despite having the same Linear, interior wall, or fenestration elements. Thus, a Baseline gets a U_assembly-0.051 / R-19.6. How is this even legitimate?

Would love to hear others’ experience with these calculations and any successful approaches.

Fellow Modelers who have working in Massachusetts or with the newer codes with envelope thermal bridging requirements; I am seeking guidance about how you’ve gotten nearly any envelope to work. Accounting for derating factors is taking assemblies that would normally be good or high performance and making them drastically worse in calculated performance.

For example, within the Massachusetts Appendix A example calculation: calculation:

MA Example Wall Starts

Clearfield: U_assembly – 0.045 / R_assembly -22.2 -22.2

Adding Linear Thermal Bridge – ONLY – Adds U-0.15 U-0.15

Clear field + Linear: U_assembly – 0.19 / R_assembly-5.2 R_assembly-5.2

Continuing to add the other derating factors factors

Final Assembly U_assembly-0.25 / R-4

That’s an ~80% reduction in thermal performance(?!?!?!). Even adding CI to an assembly, the derate methodology compounds to make nearly any assembly nearly impractical.

To add insult to injury the Baseline Assemblies do not have this same derating method – despite having the same Linear, interior wall, or fenestration elements. Thus, a Baseline gets a U_assembly-0.051 / R-19.6. How is this even legitimate?

Would love to hear others’ experience with these calculations and any successful approaches.