Work on the design of the new building began in the summer of 1999. The North, Garden and West Wings as well as the adjacent Dorsett Hotel were demolished to make room for the addition. Building 11 and the Johnson Wing underwent substantial renovation.

The entire mechanical and electrical infrastructure was renewed. A new central chiller plant totaling 3600 tons was installed. Plant operators are able to control plant operation to minimize electric costs as the load profile of the building changes. New gallery climate control was provided throughout. System features include new adjustable constant volume reheat air handling systems, twinned to provide for standby operation during scheduled maintenance or in the event of equipment failure. Outside air is pretreated prior to introduction into gallery air supply.

Contaminants are removed from the gallery air supply through a total of four passes of particulate filters and five passes of gas phase filters. The Museum's building automation system maintains precise temperature and humidity control, monitor and record system performance, and automatically adjust the system over time to minimize fan, cooling, and reheat energy consumption. In addition, all aspects of the Museum's electrical and sprinkler systems were modernized. Construction began in the spring of 2000. The Museum closed for 18 months in early 2003. The expanded Museum opened in November of 2004, commemorating its 75th anniversary.