The second phase of The National Renewable Energy Laboratory’s Research Support Facility (NREL RSF) completes the NREL Campus in Golden, Colorado. RNL designed the addition to be one of the most energy efficient office buildings in the world and the higher thermal constraints and new window and curtain wall system offered J.R. Butler a challenging but rewarding project. A change in the overall construction system had J.R. Butler install the windows in Rocky Mountain Prestress’s yard.