 In November 1988 , Salomon Brothers withdrew from plans to build a large new complex at Columbus Circle in Midtown and agreed to a 20 @-@ year lease for the top 19 floors of 7 World Trade Center . The building was extensively renovated in 1989 to accommodate the needs of Salomon Brothers . This led to the alternative naming of the building as the Salomon Brothers building . Most of three existing floors were removed as tenants continued to occupy other floors , and more than 350 tons ( U.S. ) of steel were added to construct three double @-@ height trading floors . Nine diesel generators were installed on the 5th floor as part of a backup power station . " Essentially , Salomon is constructing a building within a building – and it 's an occupied building , which complicates the situation " , said a district manager of Silverstein Properties . The unusual task was possible , said Larry Silverstein , because it was designed to allow for " entire portions of floors to be removed without affecting the building 's structural integrity , on the assumption that someone might need double @-@ height floors . " 
