Dark Skies Ahead

Changes to this obscure rule could leave Midtown East streets shrouded in shadow

City Terrain Development East Urbanism
Changes to this obscure rule could leave Midtown East streets shrouded in shadow. (Alan Cordova / Flickr)
Changes to this obscure rule could leave Midtown East streets shrouded in shadow. (Alan Cordova / Flickr)

The streets of Midtown East could get a whole lot darker thanks to changes in a little-known equation (outside of architecture, anyway) used to calculate shadows cast by tall buildings.

The city is looking to change a method developers use to calculate how much sunlight a building will obscure once it tops off. Crain’s reports that the Waldram diagram, as it’s called, will be toggled to encourage taller buildings in Midtown East as part of that neighborhood’s anticipated rezoning.

To illuminate city streets and sidewalks that snake through urban canyons, the formula dictates that building taper sharply as they reach towards the sky. Typically, when architects build tall, they are presented with two options: They can create classic, “wedding cake” style buildings with tiered setbacks aligned to the zoning, or they can use calculations like the Waldram formula to attain a smoother, graduated facade. Due to building codes that require multiple stairwells and additional smoke ventilation shafts, building tall becomes less efficient (i.e. more costly) as skyscrapers butt up against building codes and the formula, which applies in Midtown only.

The city is hoping that the rezoning will spur the development of more Class A office space in the 73-block district, which is losing potential tenants attracted to towers in the Financial District with larger floor plates. Consequently, proposed changes will permit towers up to 40 percent taller—and bulkier—than those currently allowed.

The Department of City Planning (DCP) estimated that the rezoning will lead to the construction of a few new towers, so it’s unlikely that the entirety of Midtown East will be shrouded in perma-dusk in the future.

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