The abrupt switch was made early this morning because the subcontractor handling the sprinkler system installation lacks all the pipe necessary in the Phase 2 area where actual conditions above the ceiling including plumbing and ductwork differ significantly from the construction plans, which were based on the original 1960s era plans for the building. Conditions above the ceiling in the northeast quadrant of the building are much more standard and the pipe required there is onsite. The switch will help avoid delays in the work on the 3rd floor overall while the pipe with adjusted dimensions for Phase 2 can be obtained.
A new phasing schedule with the sequence adjustments described above is expected to issued soon, within the next day or so.
For more information about the work on the 3rd floor and the construction project overall see the library's construction blog.