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IN 2008, two years before Burj Khalifa in Dubai became the world's tallest building at 828 metres, development officials in Saudi Arabia were already soil-testing around Jeddah city in early preparations for a building that would beat that record. By 2020, Jeddah Tower in Saudi Arabia will steal the crown with its staggering height of 1,000m when completed.
These behemoth mixed-use towers are the pride of their cities, elevating them to global visibility and much fame. But they have also drawn criticism for their excesses - astronomical construction costs going into the billions and inefficient floor plates, with large swathes of unuseable space at the top.
Despite this, there is no relenting in the human aspiration to reach for the clouds. About 16 supertall buildings of above 300m will be completed this year, shooting past last year's nine supertall buildings. Of these, 10 are in Chinese cities and four in Dubai, data from the Council on Tall Buildings and Urban Habitat (CTBUH) shows.
These numbers would be even higher if skyscrapers of above 200m are factored in. CTBUH defines supertall buildings as those standing at 300m and above. Higher than that are megatall buildings, such as the Shanghai Tower, at or above 600m.
"It's possible that we could see a proposal for an even taller skyscraper come forward before Jeddah Tower completes," says CTBUH spokesman Matt Watson.
The skyscraper race was relatively tame until the last 20 years, with Asia and the Middle East leading the charge, driven by rapid urbanisation.
Of the tallest 20 buildings by 2020, 14 of them will be in Asia, mainly China, and three in the Middle East based on current estimates. By 2020, there could be well over 100 more supertall buildings in the world, up from the current 126, going by those already under construction.
"There's a general consensus globally that dispersed, sprawling development is unsustainable," Mr Watson says. "Many cities are also seeing rapid population growth around their central business districts as knowledge workers seek a more urban living experience, which is driving up land prices in city centres and making the investment in tall buildings worthwhile."
At the global epicentre of massive urbanisation, China leads the race in terms of the total number of supertall buildings at 58; the United Arab Emirates and the US are a distant second and third respectively at 24 and 18.
It will be a challenge for any nation to catch up with China, Mr Watson points out. Even going by skyscrapers of 200m and above, China is ahead with 579 buildings, with the US a distant second at 185. Last year, China completed 84 buildings of over 200m and its closest national contender, the US, completed only seven.
China's unprecedented pace and scale in building skyscrapers is of no surprise. CBRE global chief economist Richard Barkham notes that the country needs to make sure its growing cities do not consume too much land area, particularly valuable agricultural land. Building upwards takes care of that.
Secondly, China wants to create dramatic skylines in its big cities to boost these cities' branding, which does play a role in attracting further capital. And thirdly, supertall buildings provide a modern platform for China's expanding service sector, Mr Barkham says.
The economics of building tall
While these marvels of engineering serve as giant status symbols, they have led to valid questions on whether they are truly worth it.
Most industry players can agree on the need to build dense centres of activity to maximise land use and create investment opportunities. But beyond a certain height, some think that the merits become less justifiable as escalating construction and maintenance costs compete with other infrastructural needs for capital.
Supertall buildings are also not necessarily efficient. Some of the world's tallest have been criticised for being built with added "vanity height", which serves no purpose other than to push them into the architectural category of "supertall".
At Burj Khalifa, for instance, nearly a third of its height is unoccupiable. It is among five towers in Dubai listed as the tallest buildings in "vanity height". Across these five, some 31 per cent of total space constitutes wasted space in the sky.
In a bid to outdo one another, architects have also fallen back on pointed spires to reach higher. Though One World Trade Center has a height to tip of 546.2m, the amount of useable space goes up to 386.5m, as much of the rest is a spire that works like an antenna.
But to the proponents of supertall buildings, these iconic landmarks do bring about lasting economic value.
Supertall buildings expert Andy Davids, who was responsible for some of the Middle East's most well-known towers, including Burj Khalifa and Emirates Towers in Dubai, believes that iconic buildings mark a place and increase the value of all assets surrounding that place.
"This is a very powerful driver in the business case for such projects where a master developer owns the land within the circle of influence of the supertall building and is thus able to place a premium not just on the iconic building but on the buildings around it," says Mr Davids, who is design director for tall buildings at engineering consultancy Aurecon.
These buildings also optimise the use of space and free up ground space for parks and other public spaces in cities that face pressures from rapid urbanisation, he adds.
A spokesman at Emaar Properties, the developer of Burj Khalifa, notes that developments around iconic towers are seen gaining significant value, sometimes in the range of 35-50 per cent, compared to standalone developments. And Burj Khalifa has achieved higher return on investment (ROI) than the non-supertalls.
"It is today a thriving community with residents, commercial offices, the world's first Armani Hotel, the world's highest observation deck at the top and other attractions. With strong response from investors to the residences in Burj Khalifa, it achieved revenue recognition soon after completion," Emaar's spokesman says.
"More than the ROI for the individual buildings, it is the economic value and social prestige that supertall buildings create for the community that matter."
Ross Wimer, who leads AECOM's national architecture and interiors practice, notes that Burj Khalifa has already created enormous value for the building sites that surround it, despite not being in a densely developed location with a mature public transportation system.
For instance, rooms at the Address Hotel facing Burj Khalifa command a significantly higher price than those that face the other way. Residential towers nearby are all oriented towards the landmark in the way that beachfront developments face the sea, Mr Wimer says.
According to Harmen De Jong, partner for development consultancy and research at Knight Frank Middle East, the majority of supertall buildings in Dubai have also seen healthy take-up of space, with most enjoying high occupancies averaging around 90 per cent.
Dubai may well be an anomaly. Mr De Jong notes that Dubai's office market shows a strong willingness to pay premiums averaging 120 per cent in sale prices and 61 per cent in rental rates for the supertall buildings compared to normal buildings.
The average rental rates within supertall office buildings around the world typically vary by an average of 10 per cent from lower floors to higher floors to super-high floors.
Estimates from CBRE's Mr Barkham on the rental premiums for supertall buildings compared to normal buildings are more modest - in the range of 15 to 30 per cent, depending on location, view, and quality of building.
But certainly, supertall buildings take much longer to fill up. At the twisting Shanghai Tower, the world's second-tallest building completed in 2015 at 632m tall,around 60 per cent of the available space was unoccupied, though it is reportedly 60 per cent rented out, according to an Australian Financial Review report in August.
JLL China director for property management Mike Chan estimates that it takes 24-36 months for an average supertall building of 300-600m to be filled up completely.
Counting the cost
Supertall buildings are also much costlier to build, due to their need for sophisticated foundations, structural systems to carry high wind loads, and high-tech mechanical, electrical, and fire-resistant systems.
Because a large core area is needed to accommodate elevators and building services systems, these skyscrapers are typically left with 70 per cent of useable space compared to more than 80 per cent useable space in low-rise buildings.
"Around 300m, we are finding that the cost for the foundation, structure, elevator systems and exterior wall systems begins to increase and can add as much as 20 per cent to the cost of the tower," says Mr Wimer. "In addition, the logistics of moving workers and materials vertically adds to the cost of supertall towers."
In Dubai, there is an average 8 per cent escalation in per square metre cost for every additional 10 floors that are added to a building, Mr De Jong projects.
Iconic projects with unorthodox architectural designs will cost even more, he says. Burj Khalifa, Cayan Tower, and Burj al Arab have an average construction cost of US$3,500 per sq m (psm), compared to US$1,500 psm for structurally simpler towers in Dubai like Rose Tower and Princess Tower. But Mr De Jong also highlighted that height is not the only factor as the construction cost for some residential towers in Dubai can range from US$730 to US$1,700 psm.
In China, the development cost for a supertall building in a first-tier city averages 20,000-22,000 yuan psm (S$4,080-S$4,490), compared to a normal building at around 8,000-12,000 yuan psm, Mr Chan estimates.
Supertall buildings also suffer from higher operational costs, such as high energy consumption, elevator maintenance and security issues.
Taking a first-tier city in China as an example, Mr Chan says the cost of managing supertall buildings is around 35-50 yuan psm per month, while the cost of managing a normal building in Shenzhen is around 26-30 yuan psm per month.
How much higher
Clearly,financial considerations are key in developing supertall buildings. A number that were proposed never made it to reality; some have their construction on hold due to funding issues.
"In essence, the height of a supertall building is only limited by the attention span of its investors," says Mr Davids. Burj Khalifa took over seven years to design and build. It's unlikely that owners would wait longer than 12 years, and certainly not 15 years, Mr Davids points out.
"So the real question is 'how high can we build in 12 years?' "
Most new supertall projects now tend to be mixed-use developments with a hotel, serviced apartments, residential, office and an observation deck, rather than just a single-use building.
Ever-growing housing demand plays a part in developers' decisions to incorporate residential components. The need to generate sales and quick capital returns is a bigger driving factor, market watchers say.
"Economic conditions are prone to change over the course of a project and this will limit investors' appetite for risk," Mr Davids adds.
To mitigate the risks, Aurecon works with developers on plans where supertall buildings can be built in stages, making them flexible to change in use, especially during construction. This will make them more viable over a longer term.
Some industry players have also cut construction time with simple designs that favour simple floor formwork and rapid wall formwork, as well as modular production of units off-site before assembling them on-site, Mr Davids says.
Mr Wimer notes that technologies such as Building Information Management or BIM have enabled the industry to design more precisely and more durably, increasing the speed of the design process and the performance of the towers.
It's all about the lifts
But while engineering advances such as the double-deck elevators and modern construction methods and materials have made it possible for skyscrapers to go much higher, it would still be hard for new buildings to join Jeddah Tower in the mile-high club until a breakthrough in the elevator system comes.
For now, the elevator rope is a limiting factor for buildings to go beyond a mile. Elevators using conventional cables are constrained to a few hundred metres in travel distance as longer steel cables become too heavy to hoist.
The latest technology by Finnish elevator maker Kone incorporates the world's fastest and highest double-deck elevators using lighter cables that can be hoisted up to 660m at more than 10m per second. This is being used in the upcoming Jeddah Tower.
German elevator producer Thyssenkrupp is now testing out the world's first rope-free elevator system, which if successful, will allow elevators to operate without height limits, move vertically and sideways, thus permitting far greater architectural freedom.
The company has reported that this system, Multi, can achieve up to 50 per cent higher transport capacity and reduce peak power demand by as much as 60 per cent when compared to conventional elevator systems.
A breakthrough in this could mark yet another era for skyscrapers.
Will Singapore go supertall?
IN LAND-SCARCE cities like Singapore, New York, and Hong Kong, there is hardly any choice other than to build tall because geographic boundaries limit horizontal growth.
But due to current height controls here, Singapore's tallest buildings have not gone beyond 300m to be classed as "supertall". Singapore is ranked eighth among cities globally in the number of completed buildings of over 200m.
The Urban Redevelopment Authority (URA) specifies varying building height controls for different districts in the city centre to reflect broader planning and urban design intentions. This includes making sure the buildings are of an appropriate scale in relation to the surroundings and contribute to an attractive skyline.
Singapore's tallest building now is the 290m-tall Tanjong Pagar Centre by GuocoLand, which was completed last year.
Buildings here could cross 300m in the near future with the relocation of the Paya Lebar Air Base into the expanded Changi Air Base (East) and Tengah Air Base. The government has said that this will allow for the removal of height restrictions around Paya Lebar, and over an even bigger area stretching all the way down to Marina South.
While market watchers see the need for high-density buildings in land-scarce Singapore, they are mixed on whether going "supertall" here is vanity or necessity.
JLL Singapore head of research and consultancy Tay Huey Ying feels that with meticulous urban planning, there may not be a major need for Singapore to build "supertall". But undeniably, iconic buildings spin off economic benefits, given their value as a tourist attraction and ability to draw premium occupiers.
"Height, especially if it comes with spectacular views, is valued by office occupiers as well as residents as it is associated with prestige and thus command premium rents and prices," she adds. "A downside of building tall to the society is, of course, increased crowdedness and a strain on surrounding infrastructure. However, this can be mitigated with good town planning."
Knight Frank head of consultancy and research Alice Tan notes that planners and developers have to optimise tight land plots to build sufficient spaces for the workforce and house a variety of real estate uses. Developers will also need to consider "supply and demand conditions and whether a targeted occupancy level can be reached in these supertall buildings".
AME Engelhart, director of Skidmore, Owings & Merrill, the master planner and design architect for Tanjong Pagar Centre, says building density in large Asian cities is absolutely necessary to preserve the ecosystem; so too is the creation of compact mixed-use transit-oriented urban centres.
But building up just for the sake of scaling peaks should not be the goal, she adds. "On each site and each development opportunity, we strive to set the right balance of density for that very specific site and the infrastructure required within the fabric of the city to make such density successful."
Land-use planning that sets height restrictions has impeded the building of supertall skyscrapers elsewhere, such as in Europe where concern for heritage preservation is intense.
Other factors being equal, European cities have on average 69 per cent fewer skyscraper floors (in office buildings higher than 100m) than cities elsewhere, says a 2017 study by two chief economists at CBRE Global Investors and a post doctoral researcher at the University of Groningen.