Wooden skyscrapers up to 50 storeys high could soon dot Australian skylines in a push to decarbonise and revitalize urban construction.
- Three Australian construction projects could become the world’s tallest wooden skyscrapers
- Developers pay for the natural aesthetics of wood and its sustainability compared to concrete and steel
- Engineered timber for towers like these could channel more of Australia’s plantation timber into construction without reducing access to the timber frames
Three separate plans have been submitted to build hybrid timber buildings in Perth and Sydney between 180 meters and 220 meters tall.
Each of them would more than double the height of the current world record holder, an 86.6 meter high apartment building in Milwaukee, USA.
Wooden skyscrapers are made possible by hybrid construction, which uses engineered “mass timber” around a concrete core.
Developer James Dibble, whose proposal for a 47-storey apartment building in Perth is before the state development panel, said hybrid technology puts timber on par with concrete and steel.
“There’s not really any limitation to the height beyond the limitation of physics like any other building, to be honest,” he said.
“I think a 350 meter hybrid building is possible, which is almost twice as tall [of the Perth apartment building].”
‘You can’t grow concrete’
Cement and concrete manufacturing is estimated to produce about 8 percent of the world’s greenhouse gas emissions, whereas wood naturally sequesters carbon even after the tree has been felled.
Conifer plantation trees such as pines grow fastest in the first few decades and can be harvested for construction timber when they are about 30 years old.
Between growing, harvesting and processing, timber is more expensive than concrete and steel structures, but some developers are willing to pay the premium for its sustainability credentials.
James Dibble estimated his planned Perth tower, marketed as carbon negative, will cost “about 9 per cent” more than an all steel and concrete structure.
“There needs to be a recognition that the built environment is one of the three main contributors to climate change,” he said.
“We’ve seen huge developments in terms of animal husbandry and transport, and not a lot has been done [in construction].
“And I want to remind everyone that you can’t grow concrete. If concrete were a country, it would be the third highest emitter in the world.”
Apart from eco-marketing, wood’s big selling point is its aesthetic value – a natural counterpoint to the sterile grays and whites that dominate urban design.
In 2023, Murdoch University in Perth will open Boola Katitjin, a building that fully displays its timber inside and out.
“Every time we bring people through, whether it’s visitors, whether it’s future employees – everyone instinctively goes over and touches the surface of the columns,” said Multiplex design director Jamie Cook.
“It’s really a natural material that everyone wants to get up close.”
What is pulpwood?
Pulp lumber is wood that has been engineered to strengthen it against the structural weaknesses of sawn logs.
Mass wood products such as glulam (glulam), CLT (cross-laminated timber) and LVL (laminated veneer lumber) make it possible to build wooden buildings more than a few stories high.
Similarly, hybrid constructions channel the vertical weight of the structures through a concrete core, allowing the timber to dominate the interior and exterior living spaces.
“We couldn’t build a 183m building entirely from solid wood. It’s not technically possible,” Mr Dibble said.
“Where solid wood is superior, we used it, and where it wasn’t, we didn’t. We ended up with a hybrid structure that’s 42 percent solid wood.”
He also said that superiority extended to fire and weather protection.
“Solid timber can outperform steel in terms of fire. It will self-extinguish.
However, to protect against South Perth’s high water table, a concrete base was deemed more suitable.
“It’s built with concrete, the core is concrete, the columns are concrete, but pretty much everything else can absolutely be done in timber and in those applications mass timber is superior,” Mr Dibble said.
Wood supply under stress
The wood industry calls wood the ultimate renewable energy, but there is a catch.
Australia is a net importer of construction timber and there are not enough softwood plantations nationwide to meet its future needs.
Native hardwood logging is being phased out in some of Australia’s largest forestry regions, including WA and Victoria, where Boola Katitjin gets its blonde exterior from one of a handful of domestic pulpwood producers.
And the interior of the building is not Australian at all.
“The columns, beams and CLT floorboards are all spruce, which is a European softwood,” said lead subcontractor Ian Meachem.
“The sheer volume of timber required, the Australian market is just not at a point where it can economically or viably deliver a project of this size.”
Australia’s pulpwood producers are growing to meet this demand, but some in the existing sawnwood industry are not worried about the competition.
Richard Schaffner is technical manager at Wespine, a West Australian sawmill that processes as much wood as it can into construction quality.
Even then, he said only 60 percent was appropriate.
“The balance is split roughly half and half between landscaping and packaging [wood chip products],” he said.
“Some of this could be diverted to engineered structures.
“It will not necessarily mean that we will have a shortage of timber for housing construction.”