Over the past decade, energy codes have brought a number of changes with respect to improving the performance of the building envelope both in design and construction. Most notable is the increasing importance placed on air‐leakage through the enclosure and how this often unknown value affects many of the energy efficiency metrics that define the performance of the building. Currently, there are multiple codes and standards requiring varying levels of air tightness as well as varying levels and methods of verification. As the requirements and performance implications become better understood, common design and construction practices will experience shifts toward better performance as was experienced in the early years of the USACE requirements on which the private sector codes are based.

Through a review of multiple case studies of current enclosure consulting and whole building air leakage testing, including high‐rise, multi‐family, and historic renovation, this paper will discuss these codes and standards for validity, impact and relevance. Additionally, the metrics of air‐leakage as part of the overall energy model will be discussed along with the implications of what varying levels of acceptable air leakage can have on material selection, construction type, level of quality control, and even complexity of performance testing.