The renaissance of timber structures
Image courtesy of Marks and Spencer.
Timber structures are undergoing a renaissance worldwide and look poised to make an impact in Australia. Recently completed buildings like Forte in Melbourne – the tallest timber apartment building the world – and the Nelson Marlborough Institute of Technology in New Zealand are showcasing new technologies and the way forward for large-scale construction in timber in Australia.
‘Engineered timber’ is a term which broadly describes the group of products manufactured by taking raw timber logs, splitting them into smaller component parts and then gluing them back together. This has the effect of reducing the effects of natural timber variability and ensures that we, as engineers, can rely on greater strength, better performance and more accuracy than we’ve traditionally been able to, allowing us to build higher, farther and longer than ever before. Products like Glulam and laminated veneer lumber (LVL) have been used in Australia in small quantities for a number of years but, increasingly, new computer technology is allowing these materials to be produced and shaped into more complex arrangements and manufactured more efficiently. Cross-laminated timber (CLT), meanwhile, is the ‘new kid on the block’ and looks set to make waves in the Australian construction industry, particularly in medium-rise multi-residential construction, with the 2012 construction of Lend Lease’s 9-storey CLT apartment building in Melbourne one example.
Construction using CLT has been common in central Europe since the 1990s, where floors, walls and beams are all cut to shape in factories and simply screwed together on site like a giant piece of flat pack furniture. The use of this type of timber has increased in volume by over 600 percent in Europe in the last decade, going from being a niche building material to a standard form of construction, familiar to most builders and designers.
So what’s driving demand?
Timber is the world’s oldest and only truly renewable structural resource. With the amount of carbon sequestered in a typical timber structure, we can offset the amount generated in decades of service, and some organisations are already starting to make great use of timber to drive these efficiencies. Marks and Spencer (M&S), for example, has become the world’s first carbon neutral major retailer, and has created a signature timber roof on its flagship Cheshire Oaks store in the UK, in what is one of the largest sustainable retail stores in the world. AECOM’s structural specialists worked closely with M&S to ensure the roof gave a strong visual statement of the building’s green credentials. Its manufacture used only a fifth of the energy used for a comparable steel structure while also reducing energy levels due to increased natural light.
But it’s not just the environmental benefits of wood that are leading to an increased use of timber; contractors around the world are taking advantage of some other key advantages. Computer-controlled off-site manufacture coupled with simple on-site connection details means buildings can be constructed in a far shorter timescale. In Europe this has led to a lot of timber construction in schools as the major structural works can be completed during holidays, leading to safer and less disruptive builds.
Programme savings are also often achievable on timber structures. Apartment buildings are typically able to achieve around 30 percent time savings over the duration of the project, not just because the timber can be erected faster, but also because following trades can commence work on site much earlier.
Changing perceptions
In Australia, timber is the most common material used to build residential houses, and as such, the current perception is that it’s only appropriate for design in this sector. However, the use of engineered timber for larger-scale construction has more in common with precast concrete or steel frame construction. There are also concerns around fire safety on large scale timber buildings, with a perception that they’re at more risk of burning down. In reality, however, the use of thick timber sections actually has far more inherent fire resistance than an equivalent steel structure.
Another issue is that some of the timber products are not manufactured in Australia and have to be imported. While this is unlikely to be an issue on most projects, it must be managed as part of the procurement process. Such a heavily pre-fabricated system requires more design work before construction starts, although this is typically balanced by much less coordination being required ‘on-the-fly’ during construction.
Unlocking wider opportunities
The use of timber will unlock opportunities for development on Australian sites previously considered to be uneconomical due to the implications of building with heavier materials. Furthermore, its use becomes more viable to extend on top of existing buildings, allows construction on lower quality soils and enables more development flexibility when planning the construction of buildings over rail corridors.
The future of large-scale timber structures in Australia looks bright, with huge potential for timber construction to become a more familiar part of our built environment, enabling our cities to be built in a more sustainable way. Although part of this shift will be led by increased regulation around building efficiencies, an industry comprising engineers, architects, builders and developers has an important part to play to drive sustainable agendas and promote aspirational change.
Nick Hewson (nick.hewson@aecom.com) is a senior structural engineer in Melbourne.