Not What It Looks Like

by Don Friedman on February 1, 2016

This is not a seismic separation:


That’s 20 West Street (AKA the Downtown Athletic Club) on the right, 21 West Street on the left. These buildings, completed in 1930 and 1931 respectively, were constructed long before anyone in New York thought about designing buildings for the effect of earthquakes. And if you’re not designing for earthquakes, you’re not leaving a seismic separation between buildings to prevent pounding.

So why is there that very narrow space between these two high-rises? It’s hard to say. Having it is a terrible waterproofing problem: the side walls of both buildings are exposed to water and freeze-thaw cycles and cannot be maintained because the space is too small. So the masonry in that area can only deteriorate and never be fixed.

A common problem with side walls in the pre-separation era is that blind-built masonry – when the mason is working from one side of a wall and cannot see or reach the other side – is always of poor quality. Mortar squeezes out during construction and cannot be struck off the brick faces, and alignment is more difficult. Leaving even a small gap alleviates these problems. So that might be the answer.

Another possible answer is that sometimes builders are faced with contradictory surveys of the land. Pulling the construction back slightly, to the location of the innermost surveyed lot line, avoids the possibility of an embarrassing mistake in locating the building.

Finally, given that the buildings were constructed almost simultaneously, at the end of the 1920s boom, it’s possible that neither AEC team knew what the other was doing when construction began.


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