Mold was found under wall coverings on the exterior walls of a dormitory in a northern Midwest city. Determining the cause of the mold growth started with review of construction drawings and interview with involved parties. The investigation required removal of building components to expose the exterior wall construction, evaluation of the operation of the HVAC system, and review of the operation of the building during the past summer. A variety of conditions were discovered that either caused, or exacerbated the mold growth. In the first instance, installation of an air barrier under the brick facing on the building was poorly understood by the architect who designed the building and the contractor who installed it. This was not a great surprise as air barrier membranes were a new technology at the time of construction, and a membrane is thin enough that it appears as a barely visible line on construction drawings. It is not unusual for new technologies, despite being enormously useful, to be poorly understood by those involved in design and construction of buildings. Defects in the design and installation, that arose from this lack of understanding, allowed humid air into the building wall cavities, where it condensed on the back surface of wall coverings during a hot humid August, when the building was only partially occupied. This situation was exacerbated by unattended operation of the air conditioning during this period which subcooled the almost unoccupied building. In addition, details of window installation allowed humid air to infiltrate from the wall cavity into the insulated metal stud wall cavity, adding additional moisture to the situation. End dams were also missing from windows so that rain water could leak into wall cavities. Extensive graphics, including drawings, video and 3D animation were used to illustrate the problems that caused the mold growth, so that all parties could understand the causes of the mold, and properly assign responsibility for the needed repairs.