by Don Friedman on January 19, 2017

The Cathedral of St. John the Divine, on Amsterdam Avenue in Morningside Heights, has a dome roof at its crossing. The dome is of Guastavino construction, is 135 feet in diameter at its base, and very thin, with a thickness to span ratio of 200. That is slightly greater than the thickness to diameter ratio for a chicken’s egg shell. In short, the dome is a marvel of masonry design and construction.

Here’s the punchline: it’s temporary. Or, more likely, “temporary.” The plan for the cathedral was meant to include a very large crossing tower

and the dome was meant as a temporary roof during construction, to allow the interior space to be used. And then construction stalled for most of the twentieth century. And Guastavino construction became famous for its unique properties. And people came to love that huge tile dome.

Work on the cathedral may or may not continue, and if it does the building won’t be completed any time soon. As things stand, I expect the temporary dome to stay even if the crossing tower is someday (the twenty-second century?) built.

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