[+] High and Mighty: The Rise and Rise of Cantilevered Towers

Everyone loves a good levitation trick. And while magicians have been wowing audiences with them since the late 19th century, developers and architects have been in on the act too. Taking advantage of mathematical advances and modern building materials—namely reinforced concrete and steel—they have harnessed the power of the cantilever not only as a structural element but as a gravity-defying spectacle. The engineering sleight of hand has ushered in an awe-inspiring new dimension to tower design. Pushing the boundaries of the beam theory, the incorporation of cantilevers has enabled vertical construction to also increasingly extend horizontally in mid-air. Visionary American architect Frank Lloyd Wright was an early adopter, famously including a 6m cantilevered roof in his design for the three-storey Robie House built in Chicago in 1910. In the intervening century or so, however, the use of the cantilever has been taken to new extremes. Dubai’s dual tower One Za’abeel features the world’s longest cantilever— dubbed The Link, the horizontal structure measures 227m and “floats” 100m off the ground. The world’s tallest cantilevered building is New York’s 98-storey Central Park Tower, which extends 8.5m from its eastern side to maximise views from its upper level apartments. ▲ Cantilevers feature in Fallingwater House and Robie House by one of the greats of modern architecture, Frank Lloyd Wright. But the rise of cantilevered towers is not just about bragging rights. It is also being used to improve sustainability, provide efficiencies and solutions in built environments—including reducing embodied carbon and as a work-around to enable viable urban renewal and infill development on and around heritage sites. As well, it is increasingly being utilised to boost development yields and create much-needed additional living space out of thin air to cater for growing populations and the need for densification. In the past decade, a growing list of tower developments across Australia have embraced the global cantilever trend for both form and function benefits. A cantilever crowning Sydney’s award-winning One Central Park even houses a heliostat with 320 mirrors reflecting sunlight onto the ground below. “It’s always challenging because it’s gravity defying,” DKO Architecture director Raymond Mah says. “It’s not a new thing but we are doing a lot more cantilever buildings and there’s good reasons for it. “As cities get denser, daylight as a commodity becomes a lot more precious and buildings are twisting and cantilevering to really pre-empt that. “Otherwise if every tower just goes straight up, then they’re all just blocking out each other’s views and daylight. “But also because we’re always balancing the need for great design and also a great development outcome for our clients, using cantilevers is a good way to respond to heritage constraints and to grow the building bigger as it goes upwards.” ▲ One Central Park’s cantilever holds a heliostat with 320 mirrors. Mah points to DKO’s design for Singapore-listed developer Hiap Hoe’s Marina Tower development at Melbourne’s Docklands. “It’s a pair of towers that are cranked at two different angles, sort of like a pair of twisted french fries,” he says. “At its highest point the tallest tower cantilevers out about 10m over shops and offices below. “And because it has a very small footprint we grabbed more air rights as we pushed outwards to really flare the apartment floor plates bigger as well as get better views. “But I think it also has resulted in an architectural outcome that really adds to the Docklands skyline.” However, Mah says that the benefits of “pushing the limits” by using a cantilevered tower design need to be weighed up against the increased engineering and construction costs. “We work with our structural engineering team from day one so we can balance the additional value created with the potential increased costs and we’re not jumping into the unknown.” Quantity surveyor and Altus Group Asia Pacific president for cost and project management Niall McSweeney agrees. “It can be horrendously expensive,” he says. “So you want to have some serious benefit in regards to it … [because] the cost penalty and what it does to your program is quite substantial. “But in some instances, it can actually be hugely beneficial and it is something that is becoming more and more prevalent.” ▲ Current cantilever proposals in Australian include the redevelopment of The Star Hotel at Geelong and a double-tower project at Brisbane’s Kangaroo Point. McSweeney says cantilevered tower development generally boils down to yield on area and “the only other reason it’s done is for the aesthetic and for the overall architectural merit”. “So, if there is a heritage structure within the actual footprint of the development and you want to utilise the air above it—yes, it’s worthwhile doing. “And it’s a good way of maintaining the heritage fabric rather than dropping in a major structural element that comes through the guts of the building and destroys its integrity as well.” McSweeney believes cantilevered tower design also is something developers will increasingly need to consider going forward. “It can't be something that is just put in the too hard basket if we're going to actually try and get the yield out of the sites and increase densification. Yes, we are definitely going to have to do it.” Six towers pushing the limits From record-breakers to protecting much-loved pubs, here are notable cantilever towers in Australia and abroad... One Za’abeel, Dubai Not a city short on ground-breaking architectural design, it’s no surprise it is pushing the horizontal limits of cantilevered tower design. Nearing completion, One Za’abeel boasts the world’s longest cantilever at a mind-bending 227m long that is 100m off the ground. It is a panoramic sky concourse—dubbed The Link—connecting the mixed-use development’s two towers and will be home to Michelin-starred restaurants, observation decks and an infinity pool. The 8000-tonne cantilever, built from structural steel weighing more than the iron in the Eiffel Tower, was lifted into place in 2020. Designed by Japanese firm Nikken Sekkei, and developed by Ithra Dubai, One Za’abeel—including The Link and its dual towers rising 68 storeys (300m) and 58 storeys (235m) with four-level podium and seven-level basement—is due to open on December 1. Marina Tower, Melbourne Docklands This unique waterfront development with a tilted design comprises two inclined towers rising 44 storeys and 36 storeys, which house 461 apartments and a 273-key hotel. Designed by DKO Architecture, and developed by Singapore-listed Hiap Hoe as its debut flagship development in Australia, the towers are conjoined up to the 21st floor and then diverge at five- degree angles with floor plates cantilevering in opposite directions. At its highest point, the tallest tower cantilevers out about 10 metres. The design concept was aimed at achieving larger apartments at the upper levels and better viewlines as well as an “expressive and dynamic form that makes a distinct contribution to the rich tapestry of Melbourne Docklands architecture”. The Castle, Sydney A mixed-use tower comprising residential, hotel and retail space that rises 37 storeys. From the 11th level it cantilevers 12m off the side and suspends over the adjoining 142-year-old heritage-listed Porter House Hotel. A cast-in-place concrete bridge, with an open passageway underneath, connects the two buildings. Designed by Candalepas Associates for United Development Sydney, it includes a 10-storey podium featuring arches and apses to complement the sandstone veneer of its historic neighbour. Sitting above a six-level basement, it accommodates 131 high-end apartments. Crowning the tower is five levels of stepped gardens, framing the sky with curved concrete elements. Jubilee Place, Brisbane One of an increasing number of towers rising above historic Australian pubs. The 15-level office building cantilevers 7.5m above the heritage-listed 1887-built Jubilee Hotel in inner-city Fortitude Valley. It was designed by Blight Rayner for developer JGL Properties and its diagrid exoskeleton structure—the tallest in Australia— was incorporated to minimise the impact on the Clem Jones Tunnel directly below the site as well as enable the building to cantilever over the hotel to create large floor plates. The office tower’s lower levels are cross-ventilated with pop-out balconies and it is capped by a roof garden with vines growing between the structure. Key to the development was the refurbishment and expansion of The Jube—as the hotel is affectionately known—and integration with the tower’s recessed podium to create an activated arrival experience. Central Park Tower, New York The world’s tallest cantilevered building, it rises 98 storeys (472m) above Midtown Manhattan’s billionaires row along 57th Street. Its developer Extell Development Company acquired air rights enabling it to build above the neighburing 19th-century American Fine Arts Building. Despite some uncertainty over its design and controversy surrounding its cantilever, construction began with initial site works in 2014 and it was completed in 2020 at a final cost of $US3 billion ($4.76 billion). The skyscraper was designed by Adrian Smith + Gordon Gill Architecture. Its cantilevered section extends 8.5m from its eastern side, adding 250sq m to each floor above 88m and maximising views from its upper level apartments. Quay Quarter, Sydney Not only is it made up of five cantilevered glass volumes stacked slightly askew, Quay Quarter is also the world’s biggest upcycled building. The 50-storey tower on the edge of Sydney Harbour’s Circular Quay was designed by Danish architects 3XN in collaboration with local architecture firm BVN for developer AMP Capital. It has been deemed an adaptive reuse of global significance. Two-thirds of the beams, columns and floor slabs and 95 per cent of the of the original core of the 1976 building were retained and the new tower constructed on and around it, saving 7500 tonnes in carbon dioxide emissions if it had been demolished and redeveloped. Its stack of cantilevered Jenga-like blocks reduce the amount of direct sunlight entering the tower by up to 30 percent, eliminating the need for internal blinds while offering uninterrupted views of the harbour. You are currently experiencing The Urban Developer Plus (TUD+), our premium membership for property professionals. Click here to learn more.

[+] High and Mighty: The Rise and Rise of Cantilevered Towers

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