Cross-laminated timber (CLT) -layers of wood glued together under high pressure with the grain of each perpendicular to the one before and glulam – glued-laminated timber – will be used to erect the 45-metre tall structure set to tower above other engineered timber schemes.
The development is a timely one. In May 2016, Australia’s National Construction Code was changed so timber products could be used in buildings up to 25 metres high, without developers having to go through costly additional processes such as getting fire engineering approval each time.
The panels are then put into shipping containers and delivered to the construction site, where builders slot them into place.
Risks currently associated with prefabricated engineered timber include;
- New technology – there are not as many players in the market.
- Location of material – generally sourced from overseas at the moment.
- Grid size is crucial is developing the right structural price, the larger the grid the cost starts to increase rapidly.
- Acoustics – need to add access floor or modified built up floor.
- Waterproofing the roof, bonding of membrane to timber.
- Working in restricted sites, need a location nearby to unpack and assemble materials prior to site installation.
- Supply chain – may require 6 month lead time.
With so much of the construction process taking place in an offsite factory, builders are less exposed to onsite risks such as accidents, weather delays, vandalism and theft, which helps make projects faster, cheaper and more predictable.
As for fire safety; CSIRO testing has demonstrated that while CLT and glulam structures get a char on the outside, the structural integrity is maintained through an intense fire event. In addition, as these timber structures sit on a concrete podium to isolate the timber from the ground, so there is no issue with termites.
While engineered timber may be more expensive than concrete by a factor of 30%-40%, this is offset by savings in construction time (10% – 20%), reduced materials wastage, and reduced on-site labour costs. In addition, follow up trades can start sooner without the need to back prop, and there is a need for fewer trades (Limited structural trades, could be one carpentry crew rather than a standard Concrete, Reo, Formwork army).
“It is an essential requirement to fully design and detail a building before manufacturing commences. The digital plans are sent to the manufacturer, where computer-controlled machines produce the timber elements to the exact dimensions required, right down where electrical wires will be chased down to light switches.”
AIQS CEO Grant Warner.
The manufacturing process also reduces overall construction time to further reduce the building process impact on the environment. Manufacturing and site preparation and infrastructure work can run simultaneously.
With a lower carbon footprint than other building materials, the CLT production process produced zero waste, and timbers are typically sourced from certified sustainably managed forests. In addition, pre-fabricated engineered-wood is faster to work with and more environmentally friendly.
As demand increases for inner-city dwellings, it is likely more developers will turn to timber, for a quicker, less-disruptive option for high-rise structures.■
Grant Warner – CEO, Australian Institute of Quantity Surveyors (AIQS)