The existing upper deck was completely rebuilt in the early 1970s after the Bears left, and that was all done in the offseason. Of course, that was a build in-place, and this time they will also be adding the external concourse. David is correct in saying that the steelwork necessary for the new concourse has been completed on the 3B side. Massive "x" beams are visible in the photos at BCB. They will have to tear up portions of the 3B concourse to build access from the Cubs' dugout. Looks like they will go in underneath the new gate.