You’ll have heard of plant-based diets, but the push for plant-based cities may be less familiar. Nevertheless, it’s well under way. Research teams around the world are racing to create proposals for huge skyscrapers made of engineered timber while, closer to the ground, wooden buildings are already sprouting up in areas previously dominated by concrete.
The proponents of using wood as a construction material point to its sustainable credentials. Concrete – the world’s most popular building material – has a huge carbon footprint, accounting for eight per cent of the world’s carbon dioxide emissions, according to think tank Chatham House. Timber on the other hand can reduce carbon dioxide. According to Dr Michael Ramage, leader of the Centre for Natural Material Innovation at Cambridge University, every tonne of timber expunges 1.8 tonnes of carbon dioxide from the atmosphere.
With this in mind, Ramage and his team are reaching for the skies. They recently showcased three proposals for timber skyscrapers in London, Chicago and the Hague. The London proposal, called Oakwood Timber Tower, would stand 300 metres tall and be integrated within the Barbican. Don’t expect to climb this particular tree house any time soon however – Oakwood is still in the research stages, with a cross-disciplinary team working at every level, from the microscopic cellular structure of the wood to the response of the tower to strong winds.
If Oakwood is built (Ramage says that ‘each design is closer to reality’) it will dwarf the timber buildings currently in existence, though they too are reaching ever higher. At 85.4 metres tall and with 18 storeys, the Mjøstårnet in Norway currently holds the record for the tallest timber building. Completed in March 2019 it took its crown from the 53-metre Brock Commons Tallwood House in Vancouver, British Columbia, the government of which doubled the height limit for wood-frame buildings this July.
Buildings such as these are only possible due to innovations in engineered timber, in particular cross-laminated timber (CLT). CLT is made by gluing smaller pieces of wood together to create strong, uniform planks. Each layer of the engineered boards is usually oriented perpendicular to the adjacent layers. Much of the wood used to make CLT comes from the pine forests of northern Europe, Canada and the US, and Ramage highlights that as long as sustainably managed forests are used as a source, the trees are replenished much faster than their eventual occupants. He claims that the ‘sustainable forests of Europe take just seven seconds to grow the volume of timber required for a three-bedroom apartment’.
There are hurdles to be met when building with wood, the most obvious being the risk of fire. Ramage explains that most CLT has a lower fire-risk compared to other types of wood due to its size. ‘We’re building with things that are now on the scale of tree trunks and in some cases even bigger, whereas previous buildings were on the scale of branches,’ he says. ‘It’s still wood so it’s still combustible, but it’s much less flammable.’ Nevertheless, a range of additional techniques, including flame retardant paint, are necessary to bring timber buildings in line with modern safety standards.
On the other side of the world, another plant that grows in abundance is also gaining in popularity as a construction material. Bamboo is light, fast-growing and plentiful – there are more than six million hectares in China alone, almost four times the size of Wales. Liu Kewei is the head of the INBAR Global Bamboo Construction Task Force, an international group that promotes the use of bamboo and rattan in sustainable construction and design. For her, the goal is not so much height, but versatility.
‘There’s no reason why bamboo can’t provide a low-carbon replacement to a number of emissions-intensive materials, including cement, PVC and steel,’ she says. ‘In China we are seeing bamboo used not only to build houses and scaffolding, but also storm-drainage pipes, pavements, utility poles, street lights, wind turbine blades and even shock-resistant exteriors for bullet train carriages.’ She adds that UN Habitat and Yale University are working to develop 3D-printed bamboo housing for disaster relief, highlighting its potential to reduce homelessness and poverty.
For bamboo structures there are pests to worry about. ‘If bamboo poles aren’t treated properly, they can crack, or become susceptible to termites or beetles,’ says Liu. She emphasises that improving international standards for bamboo construction as well as training people to build with the material will help eliminate these inherent weaknesses.
Both Ramage and Liu believe the benefits of working with materials such as wood and bamboo far outweigh the drawbacks. ‘It’s worth remembering that there are over 30 million hectares of bamboo across the world, and more is being planted every year,’ says Liu. ‘As available, scalable solutions go, bamboo is a forgotten solution for construction.’
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