Abstract: With increased emphasis and interest on energy efficiency of buildings and commissioning of building envelopes and mechanical systems, reliance on a tight air barrier assembly plays a key role to minimize loss of conditioned air, which can reduce building-envelope performance and decrease mechanical system efficiency. The importance of the air barrier is often recognized, but the air barrier design and installation is not always given the attention it deserves by the design and construction team. Inadequate drawing details at transitions and intersections and improper detail construction can result in air barrier discontinuities and increased air leakage through the building enclosure. The consequences of uncontrolled air leakage can increase energy costs, promote condensation and moisture buildup issues, cause thermal discomfort, and reduce mechanical system efficiencies. In addition, competitive budgets and accelerated construction schedules can often result in poor workmanship exacerbating the extent of air barrier breaches. These consequences are often observed after building occupancy, which amplifies the total repair costs and disruption to the building occupants. The design community lacks any current industry standards for air barrier construction, particularly to address complex geometries, intersections, or transitions in building enclosures. In some cases, the construction manager and subcontractors do not have a fundamental understanding of the air barrier. As a result, breaches in the air barrier due to difficult transitions or geometries are not identified during construction and repaired. However, field testing of the completed air barrier assembly can identify these breaches. Often, consultants and third-party testing agencies rely on quantitative test methods to determine a whole-building or fenestration air leakage rate. These tests assess the performance of the air barrier assembly as a whole, but may not identify localized breaches. Field testing using qualitative methods can be more effective in evaluating the installation of the air barrier. This paper/presentation will briefly discuss quantitative testing methods and criteria emphasize quality control methods that can be employed during design and construction and provide examples of challenging building geometries, intersections, and transitions that are problematic. By employing effective quality control methods during design and construction, the risk of damage associated with a leaky air barrier can be minimized.