From skyscraper to 'plyscraper': The towering potential of timber
Engineered for strength and portability
This new approach to construction involves what's called "mass engineered timber": wooden beams and sheeting designed and manufactured for maximum strength by using a process of lamination or layering.
a result, only the first two stories of the King Street building need to be
constructed with concrete.
That firm footing is necessary, says engineer John McGuire, to establish a "construction barrier" against termites and rising damp.
Two forms of mass engineered timber are used: cross-laminated timber (CLT) and glue-laminated timber (glulam).
Glulam is used to make the large columns, beams and diagonal braces that give the building its final form, as well as providing for lateral stability; while CLT — essentially, a form of high-tech plywood — is used for the flooring and wall sheeting.
Mr McGuire says it's the combination of both that makes wooden framing a feasible alternative to steel and cement.
He says recent changes to the composition of cross-laminated timber has also made it safer.
"They used to use formaldehyde adhesives, which were toxic. Now new technologies are using polyurethane adhesives," he says.
"So, they're environmentally friendly, they're non-toxic and they give great strength."
And there are logistical benefits, because the engineered timber is prefabricated and precision-cut.
"In this particular building, the columns are set out on an 8-by-6-metre grid such that everything can fit into a 40-foot container. All the elements come out of that container and are bolted together on site," Mr McGuire says.
"That is a huge saving on the amount of [building] time on site, the number of on-site staff required, and therefore safety as well. And a minimisation of waste."
In addition, the Lego-like construction process allows for the building to be easily and cleanly disposed of at the end of its anticipated 50-year lifespan.
It's simply unbolted and shipped away, without the noise, dust and danger of traditional high-rise demolition.
Plyscrapers in the sky
How high timber-framed buildings can go is an open question.
25 King Street has been billed as the world's tallest and largest "engineered timber office building".
It rises vertically almost 45 metres. But a newly completed residential "plyscraper" in Vancouver, Canada, stretches skyward some 53 metres.
"As you go higher the wind loading on a building becomes a much more dominant force," Mr McGuire says.
"So, as you get higher you might look at hybrid designs using some reinforced concrete, maybe for the core or other elements of the building, to take the lateral stability.
"But I can definitely see that the benefits to time, safety and cost will make timber buildings a much more viable alternative for contractors, architects and structural engineers going forward."
Lendlease, the construction giant responsible for the King Street project, has now established a final-stage fabrication facility in Sydney; and late last year the University of Queensland opened its own independent Australian Research Council-funded Future Timber Hub.
"Our role is to develop not only engineering tools, but also the manufacturing tools that will allow industry to deliver better products," the Hub's Dr Cristian Maluk says.
"All developments that we're carrying out within the Hub are undertaken with industry partners and government, in order to enable safer, better timber buildings.
Dr Maluk is quick to dispel the notion that timber-framed buildings are more susceptible to fire.
"Engineered timber products have been demonstrated to be fire-safe and viable," he says.
"Timber is a combustible material, there's no question about it. And there's a public perception that a timber building is inherently less safe than a concrete or a steel building. But mass engineered timber is actually hard to burn."
'Better in every sense' — including for the environment
Underpinning the future of mass engineered timber are its environmental benefits.
Mr McGuire says all timber used in the construction of 25 King Street has been responsibly sourced.
And unlike concrete, which adds to global carbon emissions, engineered wood acts as a carbon sink.
For Planet Ark's David Rowlinson, that's a considerable plus.
"Trees absorb CO2 and one of the benefits of that is that 50 per cent of the dry weight of timber is carbon. And in the building sector that can be stored for a very long time," he says.