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Some of the tallest residential buildings in the world soar above Central Park, including 432 Park Avenue, which rises 1,400 feet and features an array of penthouses and apartments for the ultrarich.

But 432 Park also has an increasingly common feature in these new towers: swaths of unoccupied space. About a quarter of its 88 floors will have no homes because they are filled with structural and mechanical equipment.

The building and nearby towers are able to push high into the sky because of a loophole in the city’s labyrinthine zoning laws. Floors reserved for structural and mechanical equipment, no matter how much, do not count against a building’s maximum size under the laws, so developers explicitly use them to make buildings far higher than would otherwise be permitted.

The towers benefiting the most from the zoning quirk have all sprouted during the past half-decade: enormous glass and steel buildings with lavish condominiums that sell for millions of dollars. Many line the blocks around Central Park, some of the most expensive and coveted real estate in the city, and have become second homes for Chinese billionaires, European tycoons and out-of-state hedge fund investors.