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Preparing for the Future: Lessons From Hurricane Sandy

Posted: 04.14.2017 no comments


Ground floor is not quite the term for it. At a new gallery, classroom and office building under construction in the West Chelsea neighborhood of Manhattan, the main floor is more than four feet above the ground.

This is no mere design conceit. Elevated floors are an imperative in flood-prone areas like the site of the new building on West 26th Street, only 400 yards from the Hudson River. West Chelsea was hit hard by Hurricane Sandy in 2012. So was Lower Manhattan, where Savanna, the real estate investment concern behind the 26th Street building, owned two office towers that were knocked out by flooding.


“We learned a lot firsthand during Superstorm Sandy,” said Peter Rosenthal, a principal at Savanna and its director of development. Building a ground floor that is not on the ground is one way to defend against an ominous future.


To accommodate the elevated floor, the second story is set higher than usual: 20 feet above street level. The extra height also allows for a mezzanine that houses the fire alarm system and other electrical switchgear. A decade ago, this would have been put in the basement.


The only significant infrastructure in the basement is a 500-gallon fuel tank for the standby electrical generator on the rooftop. It, too, will be protected. The tank is anchored to the concrete floor to prevent flotation, Mr. Rosenthal said. The fuel pumps are submersible and will occupy watertight enclosures. The whole basement is meant to work as a kind of reverse bathtub, keeping groundwater out with a membrane made of high-density polyethylene that runs under the concrete floors and outside the walls.


The 18-inch foundation slab beneath the building is three times thicker than it would need to be in the absence of a high water table. That adds 650 tons of weight to the slab, which is anchored to the underlying bedrock. These measures will keep the basement — in essence, a watertight vessel — from bobbing like a giant cork from the upward pressure exerted by surrounding groundwater.


Read the entire article at The New York Times.