New York Times reports:
The developers William L. and Arthur W. Zeckendorf are paying a record $600 per square foot this week for unused development rights, sometimes called air rights, so that they can add floors to a planned ultraluxury tower on 60th Street in the old Silk Stocking District, according to real estate executives....developers are willing to pay a premium for development rights that will allow them to add more floors, building higher than they otherwise could.
