The original building was one of the few in the Loop to survive the Chicago fire in 1871, though about a third of it was still destroyed. William Hale, founder of the Hale Elevator Company, purchased the building in 1882 with the intention of building a 16 story skyscraper, but the bank refused until their lease ran out in 1894.
Because of the steel frame, it allegedly took less than two days to erect each of the newly added 13 stories.
Note: although this fact originally came from Chicago at the Turn of the Century in Photographs (great Sunday morning browsing), great details are available in the National Register of Historic Places, to which this was added in 1970.