Understanding laboratory uncertainty and its relation to code compliance

Many codes, guidelines, and standards have requirements for the STC ratings of walls. Often, field testing is also required to show compliance. We expect variation between the lab and field performance of an assembly, and that variation is commonly attributed to construction differences in the assembly and the presence of more flanking in the field. This approach tends to ignore any uncertainty in the laboratory performance of the assembly and implies that there is one "right" STC rating when tested in a lab. In reality, there is also variation between labs when testing the same assembly. Understanding that uncertainty allows designers to make better-informed decisions. Laboratory uncertainty is defined through inter-laboratory studies (ILS), but the last ILS for ASTM E90 was over 20 years ago and conducted on low-STC steel panels that don't represent typical construction. This presentation covers the results of a new study that included over 80% of North American accredited labs using higher performing, commonly used, steel stud wall assemblies. The authors will present the uncertainty determined by the study and discuss how consultants can use this information to better evaluate laboratory test data for code compliance.