Yesterday’s picture of the St. Paul Building (repeated above) had an interesting detail in the background. The problem of how tall a chimney should be has been around ever since people started building cities: it has to be tall enough so that smoke (and potentially burning cinders) don’t blow onto a neighbor’s roof or into a neighbor’s windows; but the taller a chimney is, the more vulnerable it is to lightning strikes, weathering, and high winds.
The rapid pace of tall-building development in New York in the late 1800s, coupled with the fragmented land ownership of lower Manhattan, meant that a related chimney problem became common: what happens when a tall building is constructed next door, and the chimney that was tall enough isn’t any more. Here’s a close-up of the picture, showing the St. Paul Building on the left and its older, shorter neighbor on the right:
Those things on the left, angled up and away from St. Paul, are chimney flue extensions for the lower building. There’s a minimum code distance that a flue is allowed to be from a neighboring building, so the extensions slope away until they reach that distance, turn vertical briefly to help ensure a decent draft, and end. The picture is clear enough to make out the metal struts supporting the flue extensions off the top of the old mansard roof.
That type of extension is problematic in cases like this, where the new building is literally three times the height of the old one. The extension simply doesn’t get the smoke far enough away from the upper floors of the new building. However, that’s a moot point, as we don’t have many of this kind of extension, because for a long time we’ve had a building-code provision that puts the onus for addressing chimneys on the people building the new building. Instead of a lot of low and angled extensions, we have a lot of tall extensions that are built into the new building, and carry the flues all the way up.
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