This presentation analyzes the projected energy consumption of two Chicago Class-A multi-tenant high-rise office buildings: 150 North Riverside and 110 North Wacker. The two buildings are similar in terms of floor plate, building height and site location. The major difference is that the timeframe for the design phase was separated by approximately five years. During that time, the allowable energy consumption requirement was reduced by 27.2 percent. The presentation explores the ways that the energy reduction was accomplished and what, if any, effect it had on the architecture. The revisions to the energy code were made primarily due to improvements in the performance of the building enclosure and LED lighting. Unless we revise criteria such as eliminating floor-to-ceiling glass, it seems that we have reached the point of diminishing returns for reductions in base building energy usage.