Cross-laminated timber earns its place in the mainstream
Sandra Edmunds | 7 February 2018
Cross-laminated timber (CLT) is a viable and cost-effective alternative for mass market commercial buildings and provides radical opportunities to slash construction timeframes and waste, according to Bates Smart director Philip Vivian.
The firm is the design team behind 25 King Street in the Brisbane Showgrounds redevelopment in Fortitude Valley. The 52-metre-high tower is set to be the tallest engineered timber building in Australia and will also hold the title for the largest gross floor area for an engineered timber office building in the world.
“I think the cutting-edge element is to show the industry that you can build quite cost effectively,” Mr Vivian told The Fifth Estate.
“What we’ve done is shown that it can be built efficiently with flexible floor plates using the CLT in a large and tall construction for the CBD fringe.”
Vivian says 25 King, which Bates Smart designed for Lendlease, will be an A-grade building, commanding the same rents as any other building in the CBD fringe – not particularly expensive.
“It is the first time that we’re building this sort of very cost-effective commercial office building.
“I think this is really saying – in much more of a mass market – this is a viable alternative. And that’s really an innovation in itself, to really rigorously go through and examine this project from a cost efficiency point of view and show the market that it’s absolutely possible.”
Speed saves money
Vivian says CLT enables a complete shift in the speed of onsite building.
“One of timber’s core benefits is that you can have a lot less time on site and that results in cost savings to the building,” he says.
“We’ve just been working on some prefabricated project buildings that have to be built in 10 weeks. Now, if you look at traditional construction, they are radically shorter time periods.
“You would normally be looking at, typically, buildings of that scale taking 18 to 24 months to build on site.”
An 18-storey student accommodation tower in Vancouver was built last year in just 66 days. Designed by Acton Ostry Architects, the Brock Commons Tallwood House at the University of British Columbia features 404 student beds and is the world’s tallest mass wood tower.
Vivian acknowledges the way these buildings are procured does need to change.
“It does need to be tendered earlier to enable it to go into prefabrication,” he says. “So there’s a lot of time before it actually starts onsite where its being made in the factory and currently shipped to Australia.”
Waste reduction revolution
The other cost benefit of CLT construction is the reduction of onsite waste.
“In traditional construction there is so much wastage onsite,” Vivian says. “CLT is one of the leading-edge products in terms of developing this offsite construction, which is a revolution that is really sweeping the construction industry.
“Whether it’s CLT or prefabrication or flat packing, they’re all ways to enable construction to be had offsite to reduce the waste and to make onsite construction much quicker.”
There has been a dual motivation for using engineered timber – CLT and glued laminated timber (glulam) – in the construction of 25 King.
“In one part its environmental sustainability, use of timber; and in the second part there’s the productivity benefits of creating a workplace of greater wellbeing and connection to nature,” Vivian says.
“Probably the most exciting [sustainability benefit] is the ability for the timber to sequester carbon dioxide from the atmosphere so there’s a massive reduction in carbon dioxide as timber grows.
“Even after its placed in the building, the timber does continue to sequester carbon out of the atmosphere – even though it’s not in a living tree – so it continues to have environmental benefits.
“There’s actually been estimates that if timber was used in place of all concrete and steel buildings in the world, you could cut CO2 emissions by 31 per cent – which would obviously have a huge impact on climate change.
“That would be a huge shift in the industry to say we are not building in concrete and steel anymore, but that’s quite an exciting impact for architects to have on climate change.”
How high can we go?
There aren’t necessarily any limits in CLT construction, according to Vivian.
“At Bates Smart we have already been working on timber buildings that are 22 storeys high,” he says.
There are several proposals – one in London and one in Chicago – for very high-rise buildings up to 300 metres tall.
“The real challenge is in the settling of timber,” he says. “So as you go higher, you get more weight on the timber and does it settle and does it settle differently to its core? Do the columns in the core have a differential settlement?
“Those challenges occur with steel and concrete as well, so it’s not unique to timber. It’s just a matter of working out a methodology to overcome those challenges.”
The challenges for commercial timber buildings
Unlike residential buildings, which have many enclosed spaces and therefore load-bearing walls rather than beams, commercial office buildings require large open spaces.
“We typically end up working with grids of six metres to about eight or nine metres and you do have beams,” Vivian says. It’s quite a small structural grid for an office building compared with concrete or steel.
“But there has been a shift in office building markets to say we don’t necessarily need column-free space to have a great space,” he says. “We’ve managed to get over that hurdle, which has really helped facilitate timber buildings with their shorter structural spans being built.”
Also, it’s still possible to have a flexible floor plate with columns.
“In both of the two buildings we’ve looked at – an 11-storey building and a 22-storey building – we have a side core, which gives us an open flexible floor plate.
“It typically has a smaller column grid but … over the past 10 to 15 years there’s a strong movement towards some of the older warehouses, some of the piers down on the harbour, which are timber buildings that have these smaller column grids.
“Tenants have worked out there’s not a huge loss in efficiency of having this number of columns on a floor plate but there is a huge benefit in the sense of wellbeing and connectedness of people to their workplace in timber buildings – where you can see and understand the construction – as opposed to being in an anonymous concrete office building with ceiling tiles everywhere.”
It’s this sense of wellbeing that’s one of 25 King’s strongest assets.
“When we’re doing a timber building we want to express as much as the timber as possible both on the inside and the outside of the building,” Vivian says.
The interior features exposed timber beams.
“We do that by grouping all the services inside the building and so when you’re looking up, first of all you maximise the ceiling height. Second, you are in a warm timber shell,” he says.
“Also the building has a CLT core, which we’re exposing on the inside – so that ability to connect with nature; that sort of biophilic connection where people can actually see, touch and smell timber.”
The window glass will be as clear as is possible without impacting on the building’s environmental performance.
“So when you’re outside the building, you can see in and you see this wall of timber structure,” Vivian says.
In addition, timber columns will be exposed in the 54-metre-long colonnade, which will be lined with cafes and restaurants.
“There’s a series of V-columns that hold up this lightweight verandah-like element in the front of the building and we expose the CLT so when people are walking past it they can feel and touch it.”
Despite the uptake of CLT in Australia, Vivian doesn’t envisage any problems with supply.
“The CLT industry in Europe is much more advanced than it is in Australia so they have a large number of manufacturing plants; they are growing a lot of timber.
New Zealand has already started manufacturing CLT, and plants are being set up in Australia.
“As this gathers pace, I think we will see a lot more production in the southern hemisphere,” Vivian says.
“And I don’t think there is any issue with manufacturers keeping up with demand – although it would be a great problem to have!”
Bates Smart has incorporated engineered timber into the design of the new commercial tower for 1 Denison Street, North Sydney. The podium of the building, which will be the studio floors of Channel 9’s news and current affairs, will be timber with a typical glazed facade above.
“Again, it’s near the base of the building and it’s about creating a more humane environment,” Vivian says.
“We’re trying to rejuvenate the laneways and create great public places with retail and outdoor dining and we’re using timber as a way to really make it a more warm, humane environment.”
Great for extensions
In Melbourne, they’re adding 10 storeys to an existing building of six storeys at 55 Southbank Boulevard.
“We’re adding a hotel on top – all in CLT – and the real advantage is that CLT is much lighter so it can sit on top of the existing structure without strengthening the existing structure,” Mr Vivian said.
The existing concrete-framed commercial building was designed to take just six additional levels. By using timber, which is 20 per cent lighter, Bates Smart was able to extend to 10 additional storeys, making the serviced apartment project feasible.