This report summarizes the major findings from a field study of the Region 8 Headquarters building for the Environmental Protection Agency (EPA) in Denver CO. This report constitutes one of three case studies we are conducting. The overall goal of these studies is to collect whole-building performance data from selected operational buildings that are using underfloor air distribution (UFAD) as their primary means of space conditioning. By conducting a series of field investigations, the overall performance of underfloor air distribution (UFAD) buildings can be assessed with a consistent protocol that includes collecting data from utility-bills, occupant surveys, performance data from an advanced portable measurement cart, plus other available information on design, commissioning, operations, and lessons learned from conditions in the field. To conduct such case studies, CBE developed a performance assessment protocol [Bauman 2008] that includes the approaches that are briefly described below; the respective key findings accompany each discussion. A glossary of the UFAD terms used in this report is included in Appendix C.