Dubai, United Arab Emirates (CNN) — Once upon a time, the AMP Center Tower was the tallest building in Sydney, Australia. The old 1970s building came to an end and the tower’s owners wanted to replace it with a bigger, better and more energy efficient one.
But demolishing tall buildings comes with huge environmental costs, from construction waste to carbon dioxide emissions from heavy machinery.
So in 2014 the Australian investment firm AMP Capital launched an architecture competition with an unprecedented explanation: build a new skyscraper without demolishing the old one.
Dubbed the world’s first “recycled” high-rise, the 676-foot-tall tower opened earlier this year. And on Friday, it was named the world’s best building for 2022.
The greatly expanded 49-storey skyscraper, now known as the Quay Quarter Tower, retains more than two-thirds of the old structure, as well as 95% of the original building’s core.
“The tower was near the end of its life, in terms of viability … but the structure and the ‘legs’ could actually last much longer,” Fred Holt, a partner at the Danish architecture firm behind the building’s design, 3XN, said in a video interview. .
He continued: “You can’t always keep all the elements. But if you can keep the structure – where the majority of the carbon is embodied – then you reduce your (carbon) footprint.”
After removing irreparable parts from the old building, construction workers erected a new one next to it, which they then “grafted” with what was left.
A contemporary glass facade wraps around them to create a single skyscraper.
The new design doubled the building’s available floor space, and therefore the number of people it could accommodate, from 4,500 to 9,000 people.
The architects believe their approach saved 12,000 tons of carbon dioxide compared to tearing down the tower and starting from scratch, enough to operate the building for more than three years.
As well as reducing the use of carbon-intensive materials such as concrete, the scheme is also likely to save up to a year of construction time.
“The greenest building is the one that’s already there,” Holt said, quoting Carl Elefant, former president of the American Institute of Architects.
The ambitious project, which 3XN completed with engineering firm Arup and Australian architecture firm BVN, presented a host of design challenges.
One of the first is to determine whether the existing building matches its original design.
Tall towers often collapse under their own weight, especially during the first few months after they are completed.
As a result, the center of the old AMP was “at a slightly different level than it was in the diagrams,” Holt said.
Only when construction began in 2018 were the architects and engineers able to carefully assess the existing building.
Concrete samples were used to calculate the amount – and location – of the additional structural load that could be supported.
The fact that the buildings shortened over time also presented another dilemma, what if the old and new structures warped as the first structure slowly shrunk?
To counter this, engineers installed hundreds of sensors around the building to detect even the smallest movements.
This data feeds into what Holt describes as a “digital twin” – a dynamic computer model of the tower, which was used to make real-time adjustments and ensure “everything is working the way it’s supposed to”.
Workers also left a 4 meter gap between the new and old buildings until the final stages of construction, giving the new concrete time to set before the final ‘mixing’ was carried out.
Part of a larger A$1 billion ($670 million) redevelopment project, 3XN’s stunning design features five stacked structures that spiral into the sky.
Described by the architects as a ‘vertical village’, the Quay Quarter features retail and office space overlooking the Sydney Opera House, as well as a series of rooftop terraces.
Looking from the outside, there are no visible remnants of the former 1970s building.
Also in the interior design, the two parts of the tower are seamlessly “blended”, said Kim Herforth Nielsen, founder and creative director of 3XN.
“When you’re there, you don’t think about where the old structure is and where the new structure is,” he added, noting that was crucial to the design.
Meanwhile, the building’s green credentials have drawn praise from organizers of the World Building of the Year Award, which was awarded to the Quai Quarter Tower at last week’s World Architecture Festival in Lisbon, Portugal.
In a statement, event program director Paul Finch called the skyscraper “an example of adaptive reuse.”
For the tower’s owners, the design achieved another important achievement, as it was much cheaper to build than to build from scratch.
Holt estimates that AMP Capital saved A$150 million, or $102 million, by saving the original structure.
As such, 3XN hopes the tower will serve as a case study not only for architects and other engineers, but also for building owners and business owners.
Nielsen added that the project demonstrates how “value and sustainability come together economically.”