Biofore-Magazine-2021

By Beetle Holloway Photography UPM

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FEATURE

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As cities grow in size, their increasing weight is impacting the very ground they stand on. Could shifting from concrete to wood in the construction of new buildings make our cities lighter? W hen trying to shed a few pounds, humans tend to eat better and exercise harder. But when you are a heavily populated city, weight-loss solutions are rather more complex. From residents and vehicles to buildings and infrastructure, not to mention consumables such as food, water and fuel, the world’s cities are getting heavier.

8% of the world’s CO 2 emissions. Timber, on the other hand, is lighter than conventional building materials, requiring less energy and time to produce and assemble. “There is a clear environmental aspect to building with timber,” says Antti Koulumies , Senior Vice President of UPM Timber. “The alternatives to timber – concrete, steel and aluminium – are very energy-intensive and have a high carbon footprint. Timber is the op posite. It stores carbon, particularly when used in buildings, as it is stored for a long time.” Wooden buildings are also easier to customise and design, as “there are different grades of timber, which can be optimised for usage, such as cross-laminated timber, which increases the strength and is used in building apartment blocks out of wood,” explains Koulumies. Timber’s suitability in construction is further strengthened when it is sourced from sustainably managed forests. Studies show that ma ture trees absorb less carbon dioxide from the atmosphere. Through regular harvesting and replanting of forests, carbon absorption is in creased. Shifting to lighter cities From the 85-metre wooden Mjøstårnet building in Oslo to the pro posed 350-metre timber tower inTokyo, cities’ skylines could soon re semble forest canopies in terms of material and environmental bene fits, but Koulumies believes there are awareness and cost questions to be answered first. “Five or 10 years ago most people looked at the cost and design of their building materials, not their environmental aspects,” he says. “Although this is now more important, as an industry we still need to domore analytical proving of the positive benefits of wood as amateri al and rectify some of themisinformation, such as when you cut a tree, you’re releasing carbon. Wood is completely renewable.” Only timewill tell if “urban forests”will be a feature of the future. In the meantime, while cities are unlikely to take out gymmemberships any time soon, replacing their construction diet of concrete with tim ber could see an improvement on the scales.

US Geological Survey geophysicist Tom Parsons recently estimat ed that his home city of San Francisco weighed 1.6 trillion kilograms – roughly equivalent to 290 million African elephants – not including the weight of utilities, roads or bridges. With almost 70%of theworld’s population expected to live in urban areas by 2050, the increasedweight of global cities poses a range of en vironmental and societal challenges. How do heavy cities impact the environment? In a word: subsidence. Subsidence is when the ground’s surface drops due to subterranean movement, which happens both naturally – the movement of water carving caves beneath the earth’s surface, for ex ample – and increasingly due to human activity, such as pumping groundwater and urbanisation. “When you put up a big structure, it’s going to sink and it sinks a fairly significant amount, but once it settles, it initially stays constant at that point,” says Parsons. “Yet there’s also an ongoing secondary settlement that happens when building on clay-rich soils, which can continue indefinitely such that the building keeps sinking down.” This is a particular problem in coastal cities like San Francisco, which is not only situated on a river delta but is also vulnerable to sea level rises and therefore flooding. For instance, theMillenniumTower is estimated to have sunk by more than 400 millimetres in the last 10 years, while the Indonesian government is even considering moving the capital from Jakarta, which has suffered coastal subsidence of more than twometres in the last 20 years. On a micro-scale, these consequences could damage buildings and homes by shifting their foundations, but on a macro-scale they could lead to flooding, contamination of wetlands and erosion, with Parsons warning that mitigation of these unintended effects could worsen the environmental impacts. “If you build a seawall to protect from flooding, all the erosional effects of the ocean are going to bemoved somewhere else,” he says. Could using wood be the solution? Subsidence is an irreversible process, so it’s best to apply preventive measures. With coastal migration on the rise and an estimated 60% of the buildings needed to accom modate these new arrivals yet to be built, the focus has fallen on construction. Concrete is currently the building material of choice, and its production also accounts for

Will wood make our cities lighter?

“Timber stores carbon, particularly when used in buildings, as it is stored for a long time.”