Story highlights
Most famous leaning towers are historical structures but modern buildings can also list
Although most tilting towers are safe for living, they can be tricky to correct
CNN
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From the Tower of Pisa in Italy to Britain’s Big Ben, some of the world’s most famous buildings have a distinct list. However, architectural leanings are not confined to history.
A few modern buildings – like the 541 foot (165 meter) Montreal Tower, whose 45-degree lean makes it the tallest tilted building in the world – are intentionally inclined, but those that lean without design are a property developer’s nightmare.
Wikimedia Commons
The 189 foot (58 meter) Demidov Tower -- better known as the "Leaning Tower of Neviansk" -- in Russia has an obvious lean. The top of the tower is tilted 7.2 feet (2.2 meters) from the center, an incline of approximately 3 degrees.
Although most slanted skyscrapers are safe, people don’t want to live in them as leading civil engineer John Burland explained to CNN Style,
“If residents know their building is leaning, they’re not going to be very happy – unless of course it’s leaning so much that they can charge people to go up it,” says Burland, an emeritus professor in engineering at London’s Imperial College.
Burland designed the solutions that stabilized the Tower of Pisa and Big Ben.
View this interactive content on CNN.com
The reason why some buildings develop a lean, and how such problems can be corrected, is a complex area of geology and engineering called geotechnics. CNN spoke to Burland to unravel the science of foundations and find out why he likens Pisa’s lean to children building blocks on carpet.
Wikimedia
Dedicated to the Indian God Lord Shiva, the leaning temple of Huma is thought to have been constructed between 1545 and 1560 and is part of a larger shrine, whose different parts lean to different sides. It is not known whether the temple's lean is intentional or a result of its soft riverside foundations.
CNN: Given our modern understanding of the earth and access to technology, why do buildings still end up leaning?
Burland: “We are very sophisticated in our analysis now, but we still have to understand how mother nature works.
“Mother nature lays down ground in all sorts of variable ways and unless you actually spend the money and the time investigating the ground properly – and employ people with good knowledge and experience – then you can run into big problems.”
DAVID HECKER/DDP/AFP/Getty Images
Recognized by Guinness World Records as the tower with the highest degree of tilt in the world, the 90 foot (27.4 meter) bell tower of this church in Germany has a 5.2 degree inclination. Although the building was built in the mid-1200s, the tower wasn't added until 1450.
CNN: Are leaning towers a common problem and are they safe?
Burland: “They’re relatively rare but I think when you are dealing with towers you do need to be extra careful because they reveal themselves in a way that a lower building wouldn’t.
A low building may settle a bit more at one end than the other, but most of that can be taken up within the building’s structure.
02:17 - Source: CNN
London's Big Ben tower is leaning
Most of the leaning buildings I’m involved with are not unsafe but selling space in a building that has been known to be leaning is very difficult because often the leaning is caused by some defect in construction or design.
The trouble with a tall building is that you can see it leaning, which people don’t like. It might be safe, but the owners of the building are not going to be at all happy.”
courtesy GORPROJECT
The Council of Tall Buildings and Urban Habitat (CTBUH) has released a comprehensive list of the world's twisting tall buildings that are either completed or under construction. From Shanghai to Dubai, CNN takes a look at these spectacular spiraled skyscrapers, as well as some of the other tallest buildings in the world.
JOHANNES EISELE/AFP/AFP/Getty Images
Topping CTBUH's list in terms of height is Shanghai Tower, which twirls 632 meters (2,073 feet) into the sky.
Connie Zhou/courtesy gensler
Shanghai Tower is also the tallest building in China, and the second tallest skyscraper in the world after the famous Burj Khalifa in Dubai.
Connie Zhou/courtesy gensler
Located in Shanghai's burgeoning Lujiazui financial district and designed by architects Marshall Strabala and Jun Xia from the firm Gensler, its twisted form accommodates strong typhoon winds. The tower was completed at the end of 2015.
via lakhta center press center
Although not yet completed, the second tallest twisted building on CTBUH's list is the Lakhta Center, a tower in St Petersburgh, Russia.
via lakhta center press center
Designed by British architect Tony Kettle in conjunction with Gorproject, the tower has a projected height of 462 meters (1,516 feet) and is due to be completed by the end of 2018.
Bjarke Ingels Group
'The Eleventh' towers in Manhattan, New York, will have a rotating aesthetic that gives the appearance of movement. The towers, designed by Bjarke Ingels Group, will stand 300 and 400 feet tall when they are completed in 2019.
designed by Andrew Bromberg at Aedas
A residential skyscraper in Dubai Marina, Ocean Heights stands 310 meters (1,017 feet) tall and has 83 floors. The tower is the second highest twisting tall building that's been completed and was designed by American architect, Andrew Bromberg from Aedas.
KARIM SAHIB/AFP/AFP/Getty Images
Completed in 2013 and designed by Skidmore, Owings & Merrill, Cayan Tower soars 306 meters (1,005 feet) into the sky. It's the third tallest twisted tower in the world that's complete, according to CTBUH.
courtesy GORPROJECT
A white ribbon wraps around Moscow's stunning Evolution Tower, which topped out at 246 meters (807 feet) when completed in 2015.
courtesy GORPROJECT
Inspired by the city's St Basil Cathedral and Russia's never completed Talin's Tower, the chief architect for design was Philip Nikandrov, from Gorproject.
JOHAN NILSSON/AFP/AFP/Getty Images
The world's first ever twisted tall building was the 190 meter (623 feet) Turning Torso, which was designed by Spanish architect Santiago Calatrava and completed in 2005.
AFP/AFP/AFP/Getty Images
"The unconventional form of a twisting building means every component of tall building design must be rethought," says the CTBUH report author, Shawn Ursini.
Iwan Baan/courtesy MAD Architects
Dubbed the 'Marilyn Monroe' towers by local residents due to its fluid, natural lines, Absolute World Towers was designed by MAD architects.
Tom Arban Photography Inc
Absolute World's two twisted towers stand at 176 meters (577 feet) and 158 meters (518 feet) tall.
istockphoto
Claiming the crown for the world's tallest building upon its completion in 2010, the Burj Khalifa stands a massive 198 meters (650 feet) above its nearest completed competitor.
image courtes of emaar / via aurecon group
However, the Burj Khalifa's 828 meter (2,717 feet) mark on Dubai's skyline may soon be eclipsed by a new mega-tall skyscraper.
image courtes of emaar / via aurecon group
Although not yet officially named, 'The Tower' at Dubai Creek Harbour will be 100m taller than the Burj Khalifa.
image courtes of emaar / via aurecon group
The Santiago Calatrava designed tower is expected to be completed in 2020 and will hold ten observation decks in its oval-shaped peak.
Jeddah Economic Company/Adrian Smith + Gordon Gill Architecture
Also competing for the title of the world's tallest building is Jeddah Tower in Saudi Arabia. Designed by Adrian Smith + Gordon Gill Architecture, the tower aims to break the 1 km (3,280 feet) threshold upon its expected completion in 2019. Such innovation doesn't come cheap - the building is expected to cost
$1.23 billion.
Taking the race to even further extremes, a proposal for a tower double the height of the Burj Khalifa was unveiled In Feburary by Kohn Pefersen Fox Associates (KPF) and Leslie E Robertson Associates (LERA).
Kohn Pedersen Fox
The 1,600 meter -- one entire mile -- tower is part of a future city concept named "Next Tokyo 2045," which envisions a floating mega-city in Tokyo Bay.
DBOX
In December 2015, plans were unveiled for 1 Undershaft -- a 300 meter (984 feet) tall building that could become the City of London's tallest skyscraper.
DBOX
1 Undershaft will sit across the river from London's existing tallest building, The Shard, which sits 309 meters (1,013 feet) above London at its highest point.
Courtesy CIM Group
432 Park Avenue, the tallest all-residential tower in the western hemisphere, opened its doors in December 2015 and recently became the hundredth supertall building in the world. The 425.5 meter (1,396 feet) building was designed by Rafael Vinoly of SLCE Architects.
STAN HONDA/AFP/AFP/Getty Images
Known as the "Freedom Tower," One World Trade Center stands on part of the site previously occupied by the Twin Towers. At 541 meters (1,776 feet) it's the highest building in the western hemisphere, and cost $3.9 billion according to
Forbes. The building was designed by
Skidmore, Owings & Merrill.
Taiwan Tourism
The first skyscraper to break the half-kilometer mark, Taipei 101 stands at 508 meters (1,667 feet) tall. Designed by C.Y. Lee & Partners to withstand the elements -- including typhoons, earthquakes and 216 km/h winds -- Taipei 101 utilizes a 660-tonne mass damper ball suspended from the 92nd floor, which sways to offset the movement of the building.
ChinaFotoPress/Getty Image
Construction of Shanghai's third supertall building took 11 years, but the skyscraper dubbed "The Bottle Opener" was met with critical praise and high-end residents when it was completed in 2008. At 492 meters (1,614 feet) tall, the Kohn Pederson Fox building's residents include the Park Hyatt Shanghai and offices for Ernst & Young, Morgan Stanley, and BNP Paribas.
ANTHONY WALLACE/AFP/AFP/Getty Images
Hong Kong's tallest building has 108 floors -- but walking around it, you'd get a different story. The city's tetraphobia -- the fear of the number four -- means floors with the number have been skipped and the 484 meter (1,588 feet) tall International Commerce Center is marketed as a 118-story skyscraper. The building was designed by Kohn Pedersen Fox.
Goh Seng Chong/Bloomberg via Getty Images
The joint eighth highest completed skyscraper is still the tallest twin towers in the world at 451.9 meters (1,483 feet). Finished in 1996 and inaugurated in 1999, it's been the site of numerous hair-raising stunts. Felix Baumgartner set a then-BASE jump world record in 1999 by jumping off a window cleaning crane, and in 2009 Frenchman Alain Robert, known as "Spiderman," freeclimbed to the top of Tower Two without safety equipment -- and did so in under two hours. It was designed by Cesar Pelli.
Teddy Cross
Completed in March 2016, the Lotte World Tower is Seoul's first supertall skyscraper, and currently the sixth tallest building in the world. At 556 meters (1,824 feet) tall, the building was designed by
Kohn Pedersen Fox Associates.
CNN: What are some of the foundation issues that can cause a tower to tilt?
Burland: “The ground may have softer or weaker spots which you haven’t detected. There can be unexpected geological faults, or you may not have gone deep enough with your ground investigation.”
There can also be design issues and, quite often, depending on the type of foundation, there’s construction control issues, for example on the installation of piles. So there are many causes of problems that range from the ground through to design right through to construction control and supervision.”
KARIM SAHIB/AFP/AFP/Getty Images
Built 900 years ago, this mosque is better known by locals as al-Hadba' -- or the hunchback -- due to its tower's distinct tilt. The 150 foot (45 meter) minaret is one of the few original elements of the medieval Nur al-Din complex, which has been placed on the World Monuments Watch due to its risk of destruction. UNESCO is working with the Iraqi government to safeguard the icon.
CNN: Looking at modern buildings, are the geotechnical problems that occur more the fault of mother nature or human error?
Burland:”If it’s mother nature then it’s human error because they haven’t investigated it properly.
Wikimedia
Now a famous local tourist attraction, this slanted brick and wood tower is 84 feet (25.5 meters) tall and was originally used as a water tank and -- thanks to the large clock on its top -- a time keeper. The weight of the water and the soft ground beneath the tank have caused it to lean to the southwest.
There’s this clause in most contracts about unforeseen ground conditions, which is designed to protect contractors. But if it’s unforeseen then the ground investigation, or its interpretation, has not been adequate.”
Wikimedia
The fantastical Nationale-Nederlanden building in Prague -- or "Fred and Ginger" as it's colloquially known -- was designed by American architect Frank Gehry to have an intentional lean.
CNN: How do you stabilize or center a leaning tower?
Burland: “In principle, it’s simple – and that’s the essence of genius isn’t it, simplicity – but actually it requires a lot of expertise.
You’ve got to find out why it’s leaning, so you’ve got to spend a lot of money investigating the ground around the tower (and) what’s happening over time.
The classic solutions involve what’s called compensation grouting or injecting grouting into the ground to try and lift one side of the building compared to the other. It has to be carefully controlled, and it uses very specialized equipment.
Pablo Blazquez Dominguez/Getty Images Europe/Getty Images
Also know as the "Gate of Europe," these twin office towers designed by American architects Philip Johnson and John Burgee rise 373 feet (114 meters) into the sky at an angle of 15 degrees.
Or you can cut the building at its foundation level to insert jacks and jack the building straight, that has been done many times.
At Pisa, because the ground was so incredibly soft, we did the opposite and took some ground out.
But it’s not something you rush into … you can get it terribly wrong if you haven’t got the techniques to do it properly.
Wikimedia/gilibean
Leaning 9.5 feet (2.9 meters) from its center, the "Crooked Spire Church" as it's also known was built at the end of the 13th century and completed around 1360. Although designed to be straight, it is thought that the lead weights used to cover the spire caused its green timber frame to warp and lean.
CNN: Why was stabilizing the Tower of Pisa so difficult?
Burland: “Pisa is rather special and it becomes highly technical but the best way is to give an analogy.
The ground Pisa is built on is very compressible indeed, and the reason for its leaning can be explained by the way most children will try and build towers on the floor with wooden bricks.
02:18 - Source: CNN
Is this the world's craziest new skyscraper?
They will know that if you are on a solid wooden floor you can build a tower that’s quite high, but if you start building it on a carpet, you can only get to a certain height and then it starts to lean. However hard you try you can never get higher.
That’s because once the tower begins to move, even a little bit, the center of gravity moves and it drives the tower even more towards the direction that it’s moving.
And that’s the reason why Pisa is leaning – it’s a bit like trying to build a tower on a soft carpet.”
Eckehard Schulz/dapd
The 184 foot (56 meter) high tower on the Church of Our Beloved Ladies by the Mountain in the German spa town of Bad Frankenhausen was first reported to be subsiding in historical documents from 1640. The tower has listed further to the northeast since that time and is now estimated to have a 4.8 degree lean. Fearing imminent collapse, the German government approved funding for restoration works to stabilize the structure in 2014.
CNN: What building do you consider to be the world’s worst titled tower?
01:28 - Source: CNN
UTEC in Peru wins RIBA International Prize
Burland: “There is a kind of joy in having the biggest leaning tower in the world … a kind of competition about who’s got the world’s biggest lean, and I think I have a wry smile about it all.
STR/AFP/AFP/Getty Images
The curvaceous 540 foot (165 meter) tall Capital Gate building is now an iconic part of the Abu Dhabi skyline. Designed by British architects RMJM to tilt 18 degrees to the west -- more than four times the angle of the Tower of Pisa -- it is recognized as the "furthest-leaning man-made tower" in the world by Guinness World Records.
Really, the fact that Pisa Tower is so magnificent and so breathtaking in its architecture – it would have been a world heritage monument even if it wasn’t leaning – I think that’s really what makes it so famous really.
So it’s fun, but none of them are as beautiful as the Pisa Tower.”
This interview was edited for length and clarity.