The Energy Code does not identify where within the assembly the air barrier is to be installed. So, that is left up to the design professional based on the project type, geographic location, and their experience. 

So where should the air barrier be placed within enclosure assemblies?

Uncontrolled airflow within a building enclosure can cause damage to building components. Though our harsh winter conditions in Minnesota and areas our firm services, we have had the unique opportunity to see through our forensics investigations, monitoring of existing buildings, and extensive design consultation, areas of concern to designers, contractors, and building owners. In addition, how to prevent and remediate problems will be outlined.

Distance from heat sources, air cavities, air movement within assemblies through uncontrolled flow, and lack of interior air barriers are all considerations that should be taken into account when designing exterior wall assemblies and transitional details, especially between plane changes. When professional experience is absent or solutions are not included due to budget constraints, moisture damage still occurs in code compliant extreme cold climate buildings. Through experienced design by an Architect, upfront review and analysis from a consultant, and knowledgeable construction by a contractor, proactive measures to prevent building damage can be incorporated into construction.