City Hall has finally found a way to personally benefit from the fitful rebirth of ground zero. A year ago, Deputy Mayor Dan Doctoroff pledged that the city would rent up to a third of the office space in 4 World Trade Center if no other tenants emerge by early 2009 — a key financing commitment for the three towers that developer Larry Silverstein will soon start building. Yesterday, Doctoroff told us that the city was planning on making good on that pledge — and that relocating city workers into the new Fumihiko Maki–designed skyscraper could benefit everyone, including us taxpayers. "Too many of our workers are in substandard space," Doctoroff said, "and this gives us an opportunity to upgrade some and perhaps sell some buildings that are better used for residential." Because condo demand is outpacing the need for office space down there, this could be a deft, profitable maneuver for the city. At the same time, having a guaranteed tenant would take the heat off Silverstein (and his lenders). Since many city workers are toiling in basements and too small spaces, this could be a hat trick not even Silverstein's architects could've designed. —Alec Appelbaum