They offer robust carbon sequestering and have the potential to reach skyscraper heights, so why aren’t we building more wooden skyscrapers in cities?
Earlier this year, the CTBUH predicted that 2015 would be the year of the woodscraper. So far the predictions are proving promising with an array of tall wooden projects proposed and under construction.
However, in Australian cities and other major urban pockets where skylines are rising at a rapid rate, there remains some resistance to high rise wooden structures.
Australia has just one tall timber building reaching 32 metres and that was built three years ago.
In a country where there are currently 40 skyscrapers above 100 metres under construction or topped out according to the current CTBUH database, not one will be made of wood. A further 115 have been proposed across the nation - all to be made of concrete or composite.
It could also be an environmental step in the wrong direction.
According to professor Chad Oliver, director of the Global Institute of Sustainable Forestry at Yale University, the manufacture of traditional building materials - steel, concrete and brick - is responsible for 16 per cent of global fossil fuel consumption. That figure jumps to 20 to 30 per cent when transportation and assembly of the materials is taken into account.
Overseas, there are numerous projects on the go. Austrian real estate firm Kerbler Holding GmBH recently unveiled plans to build an 84-metre wooden-hybrid mixed-use residential and commercial skyscraper in Vienna.
The project, entitled HoHo, is estimated to cost €60 million. Project developer Caroline Palfy told The Guardian that wood was chosen largely for environmental reasons.
"We have wood, which is a perfect construction material for building," she said. "It was used 200 years ago and it was perfect then and is perfect now.”
In Bergen, Norway, the Treet wooden apartment building is currently under construction.
The 14-storey structure will house 62 apartments and will be made of pre-fabricated cross-laminated timber. It is expected to sequester approximately 1,000 metric tons of CO2.
According to the 2014 study Structural Design and Assembly of "Treet", the building will also be clad in glass and metal sheeting to protect the timber from sun and rain.
Upon its expected completion this year, the building will be the world’s tallest timber apartment building, taking the title from Melbourne’s 10-storey Forté building.
Of the completed projects, London has a nine-storey wooden residential building – Stadthaus – while late last year, Vancouver-based architect and wood advocate Michael Green completed the Wood Innovation Design Centre (WIDC) for the University of Northern British Columbia.
The WIDC is made up of 1,700 cubic metres of wood and is now North America’s tallest wooden building.
Green is globally renowned for helping drive the conversation for tall wooden buildings. He recently won the Architect Award and the Wood Innovation Award at the 2015 Wood Design Awards in British Columbia and was also the co-author for The Case for Tall Wood Buildings.
Last year, the woodscraper message reached the White House, with the United States Department of Architecture (USDA) launching a US$2 million Tall Wood Building Competition. The USDA then committed to a climate-driven initiative that would see architects, builders and engineers trained in the benefits of wood as a structural material.
So with wood making its mark across global skylines, where is Australia in the mix?
Melbourne-based Jack Haber, managing director of Tecbuild Systems, noted that there are opportunities and limitations surrounding the use of wood.
Haber noted the recently-announced HoHo project will feature concrete cores, a hybrid facade and modular timber covering more than 70 per cent of the structure. He said local factors contributed to its viability.
“Wood in Austria is a logical building material," he said. "Austria is one of the most forest-covered countries in Europe with trees covering 47 per cent of its area. As a result, much of the economy revolves around the logging industry and its related products.”
Haber added that wood is one of the most important sources of external currency for the country, second only to tourism.
"The HoHo project demonstrates that wood systems can provide structural solutions, with capabilities far greater than is generally recognised," he said. "The key to increased use of wood systems lies perhaps in a supportive policy environment and in increasing the sophistication and capacity of the local supply chain."
Haber also cited the strong environmental culture of Austria, including an investment from the country to improve the energy performance of buildings.
"Promotional programmes at national and regional levels are now being co-financed by the European Investment Bank...if projects lead to documented energy savings and or increased use of renew ample energies," he said.
This could include improvements to a building shell.
Of course, there a number of factors that must be considered when one wonders why high-rise wooden buildings have not caught on on a larger scale.
Haber acknowledged the initiatives from Lend Lease to develop more massive timber buildings, but also cited a study conducted by the Queensland University of Technology that showed building professionals face the following impediments:
- limited awareness of emerging timber technologies, maintenance costs and fire risk
- limited legislative support from government
- lack of experienced designers
- lack of experienced builders
"The hybrid approach to procurement and materiality poses some challenges to construction delivery," explained Haber. "In theory, more trades means more scheduling, coordination and site management issues."
"More important is the capacity of the Australian timber industry to supply appropriate, competitively priced engineering timber products for commercial application.”
ABARES forecasts an approximate 22 per cent increase on current sawn wood consumption by 2050, taking the country to near-capacity utilisation of its homegrown forest resources.
"The shortfall in local supply capacity to service increased timber demand is likely to lead to an approximate 100 per cent increase in structural timber imports to Australia by 2050," he said, pointing out that new plantations take about a quarter century of growth to become fully productive.
"Australia desperately needs Government to assist in facilitation new future timber resources,” Haber said.
Some experts have suggested that 30 storeys is a realistic limit when it comes to timber construction, though Haber said that may be overly ambitious in Australia.
"If you want to design a 30-storey structure in Australia, current development economics and established supply chains will overwhelmingly favour a concrete frame," he said.
Haber believes the nation should definitely consider wood in suburban low to mid-rise structures, where projects will enjoy significant construction cost advantages in addition to the environmental benefits.
Finally, there are challenges when it comes to removing the fear of fire with wooden buildings.
Haber referred to fire-induced structural calamities that have occurred in concrete buildings, including the Windsor building in Madrid in 2005 and the World Trade Centre tragedy.
"Our engineering and risk capabilities cannot foresee all possible events," said Haber. "However, timber has been a mainstay of construction for millennia.
"We know it requires maintenance, but I believe there is no reason for timber structures not to take their place in appropriate situations as part of our modern urban fabric."