Eight of the world's skinniest skyscrapers

Defined as a structure with a height at least ten times its width, "pencil towers" have become more popular in the past few years — especially in congested metropolises such as Hong Kong and New York City . Recent improvements in building materials, such as higher strength concrete, have made it possible to build thinner walls, with fewer interior structures, allowing for the construction of more unconventional designs. Here are eight of the world's most interesting examples: Architect: Shop Architects Location: New York City, United States The slimmest of the slimmest is Steinway Tower , or 111 West 57th Street. At 435 metres and 84 stories high, this residential tower in Midtown Manhattan is one of the tallest buildings in the US. However, its bragging rights come from its astounding 24:1 height-to-width ratio. Due to its slenderness, the topmost stories sway during windy weather. Designed by Shop Architects, the building towers over the 16-storey Steinway Building, where famous piano makers Steinway & Sons once had a store. Architect: BDP Quadrangle Location: Toronto, Canada Designed by BDP Quadrangle, the 54-storey tower is set to replace an office building constructed in the 1960s. However, building a 19,459-square-metre structure as a pencil tower is not without its challenges. “Every caution must be taken to avoid harm to nearby structures as well as to not prevent the already busy street from slowing to a crawl," the designers told Dezeen. "What 15 Toronto lacks in width, it more than makes up for in height," project architect Emily Li said. "Standing at 54 storeys upon completion, it will have no trouble standing out amongst its peers in the city's financial district." Architect: Adrian Smith + Gordon Gill Architecture Location: New York City, United States The second-tallest building in the Western Hemisphere is also one of the skinniest. Located at 225 West 57th Street in Midtown Manhattan, the building reaches an impressive 472 metres. Although the mixed-use Burj Khalifa is significantly taller, Central Park Tower is the tallest primarily residential building in the world. Interestingly, Central Park Tower was designed by Burj Khalifa architects Adrian Smith and Gordon Gill. Architect: Fender Katsalidis Architects Location: Melbourne, Australia Phoenix Apartments rises 28 stories or 88.5 metres high, on a site just under seven metres wide. The skyscraper was initially planned to be 40 storeys, but was reduced due to worries that it would tower over adjacent buildings. It sits on the site of the old Phoenix Hotel, owned by Aussie rules football legend Lou Richards, and a meeting place for Melbourne's newspaper journalists. Architect: Rocco Yim Architects Location: The Peak, Hong Kong Located in The Peak of Hong Kong Island, the third Tregunter tower was completed in 1993 — 12 years after the first two were built. The 66-floor skyscraper was designed by Rocco Yim Architects and is noticeably taller and more slender than its siblings, with the top floor standing at 327 metres above sea level. Architect: Glancy Nicholls Architects Location: Birmingham, England More than 116 metres tall and only 9.5 metres wide, 211 Broad Street will become the UK's first residential pencil tower when it is completed. The project was approved by the Birmingham City Council in February and promises to transform the city's skyline. The tower will include about 264 rooms, as well as amenities such as a restaurant, gym and residents' lounge. Architect: Dennis Lau and Ng Chun Man Architects & Engineers Location: Hong Kong Island, Hong Kong A luxury apartment tower on Hong Kong Island, the 252-metre Highcliff tower looms over the southern slope of Happy Valley at a whopping 75 stories. Completed in 2003, the structure has a 20:1 slenderness ratio. The tallest all-residential building in Hong Kong, a wind dampener was installed at the top to mitigate the destabilising effects of typhoons. Architect: Dennis Lau and Ng Chun Man Architects & Engineers Location: Hong Kong Island, Hong Kong A stone’s throw from Highcliff tower is another slender skyscraper named The Summit. At 220 metres and 65 stories, it is almost as tall as its neighbour. Due to the slenderness of the two buildings, the pair are informally referred to as The Chopsticks. Both buildings were designed by Dennis Lau and Ng Chun Man Architects and Engineers. Scroll through images of some of the world's most twisted towers below:

Eight of the world's skinniest skyscrapers

Marked by narrow frames and dizzying heights, we round up the pencil towers transforming skylines the world over