The Pacific Northwest National Laboratory, Oak Ridge National Laboratory, and the University of Minnesota are conducting a 3-year, multipart study of residential retrofit wall assemblies. The project is funded by the U.S. Department of Energy Building Technologies Office. Researchers will identify, test, and verify the hygrothermal performance of wall assemblies in retrofit applications. This study includes engagement with leading thermal enclosure experts from industry, academia, national laboratories, state, and federal program administrators, through an expert meeting held in Arlington, VA on April 19, 2019. In addition to the expert meeting held in April, this project will involve the formation of an ongoing, expert advisory committee. This report summarizes the discussions and outcomes of the expert meeting. References made to specific organizations or products do not constitute endorsements or recommendations.