Good morning, all,

Do any of you know why the U-values in Appendix A of ASHRAE 90.1-2013 (Table A2.3.3) for a metal building roof are different than those in the 2010 edition (Table A2.3)? In 90.1-2013 they no longer match the U-values in the tables in Chapter 5 for the given insulation system. The same is true for metal building walls. Did they change what is included in the assembly, like film coefficients, or calculate thermal bridging differently? If so, why didn't the assembly values in Chapter 5 change? Any insights would be appreciated. I didn't find any errata for this on ASHRAE's website.

Thanks,
Keith Swartz, PE, BEMP
Senior Energy Engineer | Seventhwave | Madison.Chicago.Minneapolis
(formerly Energy Center of Wisconsin)
608.210.7123 | www.seventhwave.org