Last year, the Sydney skyline got a strikingly modern addition: a 49-story office tower, built from a decades-old structure. The Quay Quarter Tower, in the city’s historic Circular Quay, stands on the site of a 1976 skyscraper that Danish architecture firm 3XN repurposed to create the new building.

More akin to a face-lift than a birth, this kind of large-scale structural reuse has clear environmental advantages. By incorporating 65% of the original building’s floor plates and 95% of its concrete elevator shafts and stairwells into the new tower, 3XN reduced the overall material needs of the project. That slashed the so-called embodied carbon emissions that would have resulted from creating new concrete and steel for construction. The architects estimate that this approach saved 13,000 tons of embodied carbon, or the equivalent of nearly 5,000 round-trip flights between Sydney and Copenhagen.

“Both from a sustainability and an economic point of view, in the future we need to reuse as much as possible of the existing structures we have around the world,” says 3XN founder Kim Herforth Nielsen.

Repurposing the structure of the old tower also shaved a year off the project’s timeline compared to ground-up construction, saving money and allowing the building’s owner, AMP Capital, to start leasing out its office spaces sooner.

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