The American Iron and Steel Institute (AISI) has published AISI S250-21, "North American Standard for Thermal Transmittance of Building Envelopes With Cold-Formed Steel Framing, 2021 Edition,” as a single source for calculating the thermal transmittance (U-factors) of walls and ceiling/roof envelope assemblies that contain cold-formed steel framing. The standard is intended for adoption and use in the United States, Canada and Mexico and is available for free download at www.aisistandards.org.
AISI S250-21 was developed to eventually supersede the many methods currently found in various energy codes and standards, most of which are limited to calculating wall assemblies at 16 or 24 inches on center framing only. The standard’s mathematical options are divided into: