"Sidewalk sheds consist of pipes, beams, planks and plywood. They can be a few feet or a few hundred feet long, and they make it possible to walk in New York without getting beaned by bricks falling off buildings. The bricks land on the sheds instead. During the real-estate boom, New York had between 4,000 and 6,000 sidewalk sheds. During the real-estate bust, New York still has between 4,000 and 6,000 sidewalk sheds. Construction sites have gone dark, but façades keep buckling and cornices keep cracking as if nothing had happened to the economy."There's also a nice slideshow.
Photo by Matthew Craig.