Most slender building

The most slender building is 111 West 57th Street (also known as the Steinway Tower), a luxury residential development in New York City, USA. The building is 435.3 m (1,428 ft) tall but only 18 m (59 ft) wide at its base, giving it a slenderness ratio of 1:24. The building was topped out on 29 October 2019.

111 West 57th Street is the latest in a sucession of narrow residential skyscrapers that have gone up along the southern side of Central Park in Manhattan (an area now known as "billionaire's row"). Others include 432 Park Avenue (slenderness ratio of 1:15) and 220 Central Park South (slenderness ratio 1:18).

This style of building has emerged as a consequence of sky-high real-estate values, which make it commercially viable to build extraordinarily slim towers on small, awkwardly shaped lots. In order to recoup the costs of construction on a tower like this, which hs a gross floor area of just 29,357 m² (315,996 sq ft) spread over 84 floors, the apartments have to sell for at least $3,000 per square foot (almost twice the average for Manhattan, which is already the highest-priced real estate in America).

These super-tall and super-slim towers have only become technically possible fairly recently, thanks to a number of technological advances. These include high strength concrete formulations and better computer simulation of wind-loading forces. To counter the predicted wind load, 111 West 57th Street was designed with what's called a "tuned mass damper" in the upper part of the building – effectively a giant pendulum whose movements counter the swaying effect of the wind.