Rapid urbanisation of cities is becoming more and more apparent. This immediately presents issues in terms of the carbon footprints of buildings. The bigger cities get, the taller buildings get, the more greenhouse gas emissions we produce in their construction. In order for us to make our cities bigger, taller, more environmentally-friendly, cities need to find ways to future-proof themselves.
By 2050, the global population is expected to rise to 10 billion, and around two-thirds of us will live in cities. Of course, the solution to this in terms of space will be high-rise complexes.
The materials we use now to build with, mainly concrete and steel, have a large carbon footprint. The answer may lie in something called cross-laminated timber, or CLT.
We are currently in a somewhat renaissance for timber. Wood, of course, is a renewable resource. Currently, the world’s tallest building at 53m tall is the Brock Commons Tallwood House in Vancouver, which was completed in 2017, just beating the then world’s tallest wooden building, the Treet building, at 52.8m, in Bergen. These however may be left in the proverbial timber dust, with a proposed building in Tokyo known as the W350 Project planned to reach 350m (although this is scheduled for completion in 2041).
In Brummundal, Norway, an 81m high residential building is being constructed from Norwegian timber. Vienna is currently working on an 84m high wooden building. In the Parisian district of Terne, an entire wooden building complex is under construction, and in Germany, an eight-story wooden house was built on an area that used to belong to the United States army in the Bavarian town of Bad Aibling. It is a current showpiece for energy-efficient construction.
Concrete and steel are both costly to produce and heavy to transport, whereas wood can be grown sustainably and is far lighter. Concrete manufacturing is the world’s third largest producer of greenhouse gases, and is also 15 times less thermally efficient as timber.
Another boon to using timber as a construction material is it’s ability to sequester carbon from the atmosphere as it grows, trapping that within it’s makeup. For example, Kielder Forest in Northumberland has 150 million trees. These trees sequester 82,000 tonnes of carbon annually. “This means that as a rough estimate each tree at Kielder is locking up 0.546 kg of carbon per year – equivalent to 2 kg of carbon dioxide.”
Credit: The Economist
It has been shown that a timber building can reduce it’s carbon footprint by up to 75% in contrast to a building of the same size made of conventional building materials. American architectural firm Skidmore, Owings, and Merrell (SOM) , who designed Dubai’s Burj Khalifa, have designed a 42m tower, which, if built, will have a carbon footprint 60% less than a conventional build.
“Wood environments make people happy”, gleefully asserted the exhibition ‘Timber City‘ at the National Building Museum, which ran from 2016 to 2017. The exhibition included “architectural models, a video about managed forests and a world map that highlights more than 30 notable recent wooden buildings.” There was also a selection of tree stumps, wood manufacturing examples, and different types of lumber waste, nearly all of which can be used commercially and are recyclable in some way or another.
Regular timber unfortunately isn’t malleable like steel or concrete – it cannot be poured and set as those materials can. It is not strong enough to build high. This is where CLT comes in. It is a wood-panel product made by gluing layers of solid-sawn lumber together, with each layer glued perpendicular to one another. By gluing the layers perpendicular, the finished panel achieves better structural rigidity in both directions.
Whole sections can be pre-made and erected quickly on-site. Due to the relative strength and lightness of the wood, it is also suitable for closing gaps, or construction projects on existing buildings.
In April, plans were proposed for an 300m high wooden building, consisting of 80 storeys, which would be integrated with London’s Barbican Centre, a scheme which was developed between Cambridge University’s department of architecture alongside PLP Architecture and the engineers Smith and Wallwork. The project, if realised, could create over 1,000 new residential units.
“If London is going to survive it needs to increasingly densify”, says Dr Micheal Ramage, director of Cambridge’s Centre for Natural Material Innovation. “One way is taller buildings. We believe people have a greater affinity for taller buildings in natural materials rather than steel and concrete towers.”
For those of you whose immediate thought is – are we not forgetting the Great Fire of London? The fires that frequented the city of Edo (The name for 17th century Tokyo)? Fortunately for those afraid of house fires, CLT does not burn like conventional timber, as the above video will testify.
“Every well-trained firefighter knows today that an adequate solid wood construction made from cross-laminated timber will withstand fire long enough for them to rescue the residents,” said architect Tom Kaden.
Using CLT and other wooden materials offers new design potential, and ultimately, space to grow. The transition from concrete and steel to construction using timber may possibly have a wider positive impact on urban environments and build form.
It is possible that these new ideas will allow architects, designers, and engineers to reformulate the aesthetics of architecture, but also the inherent structural methodologies that architecture has generally become accustomed to. New innovations in timber could lead to a greener revolution in architecture for the 21st Century and beyond.