My interpretation is that a 450k sqft. footprint * 6 floors = 2.7M sqft of total space.
If you look at the revised elevation in the app it appears that there are 5 or 6 floors, it's kind of unclear.
The initial documents refer to almost 2.7M sqft of total floor area (although only refer to 5 levels, not 6).
http://webcast.ottawa.ca/plan/All_Im...12-20-0038.PDF