Supplanted for more than a century by steel and concrete as the materials of choice for the construction of tall buildings, wood is making a comeback.
And its return is convincing a growing number of architects and engineers that it could be the building material of the future.
In fact, some have already begun designing and building high-rises almost entirely of wood.
The latest example comes from a Japanese company called Sumitomo Forestry Co Ltd. It wants to put up the tallest wood building in the world at 70 floors - 350 metres - in the hopes
that it will encourage others to follow its example and turn Tokyo into a virtual forest, making it a greener and healthier place to live.
“Tall wood buildings are capturing the imagination of architects, engineers, and developers,” reads a website linked to the Softwood Lumber Board, a U.S. industry body.
Tallest in the World
Barring any new entries in the future, Sumitomo’s project would be the tallest of its kind in the world. «The aim is to create…environmentally-friendly…cities where they become forests through increased use of wooden architecture for high-rise buildings», it said in a statement in February.
The cost – some 600 billion yen – is high, but Sumitomo expects it to come down as new technologies are developed during its construction, which is to take more than 20 years.
Given the amount of timber to be used – some 185,000 cubic metres, enough for about 8,000 houses - the green effect will be significant: the amount of CO2 fixation as carbon would equal 100,000 tonnes.
What Sumitomo is proposing is the latest case that could lead to a revolutionary change in the construction industry because steel and concrete have accompanied every single structure that has reached for the skies for more than a century. In fact, they were what made a skyscraper possible in the first place with the 1885 construction in Chicago of the Home Insurance Building, the world’s first.
This rediscovery of wood comes from the desire among builders for projects that are easier and cheaper to develop in addition to being more environmentally friendly.
A lot has to do with the innovative form that wood has recently assumed as a construction material. Technologist, a website run by EuroTech Universities Alliance, a partnership among four European universities, calls it engineered timber. Also known as cross-laminated timber (CLT), it is a series of planks that are glued perpendicular to one another.
Since CLT comes prefabricated in various shapes and sizes, it makes it easier and cheaper to erect a building than would steel and concrete. For example, a student residence at the University of British Columbia, which became the world’s tallest wood building in 2016, took a mere 70 days to go up. «New technologies advances with construction techniques and composite wood make this a very exciting area at the moment», Riccardo Tossani, an architect in Japan, told British newspaper The Telegraph in a recent article.
When it comes to its green credentials, wood outclasses steel and concrete on a number of fronts.
For one, it has a smaller carbon footprint, with trees sequestering carbon at an approximate rate of one tonne of carbon dioxide per cubic metre. The making of concrete, on the other hand, has the opposite effect, accounting for 5-8% of global emissions of greenhouse gases. «If you build a 20-storey high-rise of cement and concrete, the entire process would emit some 1,200 tonnes of carbon dioxide. Wood, in comparison, would lock up about 3,100 tonnes – a net difference of 4,300 tonnes», according to a 2017 article in Technologist.
It is for this very reason that Vancouver architect Michael Green chooses to work with wood. «Steel and concrete don’t grow back. They are not renewable materials», he told the online magazine of the Smithsonian Institution. «They are not even remotely renewable materials—they use massive amounts of energy in their creation, whereas the most perfect solar power system of making any material on Earth is the making of our forests».
When comparing it with steel, wood has a competitive strength-to-weight ratio. Its lighter weight reduces the load on a building’s foundations, making it more resilient to wind and earthquakes.
Wood also has a higher building-volume-to surface-area ratio than the two other materials, allowing for more spacious interiors.
Contrary to popular belief, it is not necessarily the building material most vulnerable to fire, so it can meet safety and performance standards required of tall buildings.
But CLT does not replace steel and concrete altogether. Since its role is essentially to serve as the structural frame of a building, the two other materials are used for high stress points such as joints, according to the Smithsonian Institution. They also fill the core of a building in one form or another to make it steadier.
Tallest in the World
To prevent deformation caused by wind or earthquakes, steel will be part of a column-and-beam structure inside the building.
Brock Commons, the student residency at the University of British Columbia, also relies one of the two traditional materials for stability. Standing 17 storeys – or 53 metres – high, it has two concrete cores.
The University’s Virtuous Example
When its completion was announced, the University of British Columbia was quick to exult its sustainability. «Wood is a sustainable and versatile building material that stores, rather than emits, carbon dioxide», it said. «By using wood, the impact is a reduction of 2,432 metric tonnes of carbon dioxide compared to other construction materials, the equivalent of taking around 500 cars off the road for a year».
Putting wood to the test will not likely stop with Sumitomo as architects and engineers throughout the world look to push the material to new heights.
In London, PLP Architecture and engineering firm Smith and Wallwork are working with Cambridge University on a proposal to build what they would call the Oakwood Timber Tower. At 300 metres, it would be the second tallest building in London after the Shard.