If you pass through Skellefteå, a city in the northeast of Sweden, it is likely that one of its most recent buildings, the Sara Cultural Center, will leave you stunned. Although given the circumstances that may not be a very appropriate expression. You will not be surprised by its 20 floors and 75 meters high, which, although not bad, are far from the dimensions of other skyscrapers. Neither because of its design, elegant and stylized, yes; but far from stunning. No. The fascinating thing about the Sara Cultural Center is in its skin and entrails: it is a tower built with wood.
And it is not the only one.
The Skellefteå block, with 30,000 square meters (m2) and which also houses the Wood Hotel, a conference centre, museum and art gallery, is in tune with a trend that has been gaining strength for years in architecture: the commitment to wood as a material to build large towers. Specifically, for the mass-timber —or mass wood— and its cross-laminated variant (CLT), which basically consists of joining several layers of solid wood in a way that differs from other options, such as glulam or nail-laminated timber (NLT).
Build with an ecological vision
Logs and planks have always been there, true; but especially from the 19th century they lost ground in the construction of large buildings in favor of steel and concrete, which have been considered more resistant. Glued and pressed wood boards are beginning to gain ground, however. Also in the construction of skyscrapers and large structures.
The data you handle The Wall Street Journal shows it clearly: between July 2020 and December 2021, the number of multi-story buildings built in the US with mass-timber it shot up 50% to exceed 1,300 structures. One of the projects is a 25-story, 86.5-meter commercial and residential block that is already being built in Milwaukee. Although it will exceed the 18 floors that the International Construction Code sets as the limit for wooden constructions, its promoters, details the New York media, have obtained the OK of the authorities.
Google has also joined the bandwagon of wooden buildings, which hopes to open one of five plants in California this summer, and relevant companies in the sector. In 2018 the Japanese company Sumitomo Forestry announced its plans to erect W350 in Tokyo, a huge building of 70 floors and 350 meters high in which wood will represent nearly 90% of the hybrid structure, which in practice represents approximately 185,000 cubic meters of material.
In 2016, researchers from the University of Cambridge, PLP Architecture and Smith & Wallwork presented the then Mayor of London, Borish Johnson, with their proposal to build Oakwood Tower, an 80-story wooden tower that would reach 300 meters in height, which would it would become one of the tallest skyscrapers in the City, crowned by the nearly 310 The Shard. Spain does not escape this trend either: a year ago, in March 2021, the Sostre Cívic cooperative inaugurated an eight-storey wooden block with 35 homes located in Barcelona.
One of the largest projects in Europe is WoHo, a 29-storey skyscraper that will reach 98 meters high and it will be built in Kreuzberg, in Berlin, with an investment of 90 million euros. To give it shape, those responsible will use concrete in the core and basement, but the structure will be built mainly with cross-laminated wood. Another reference is Mjøstårnet, a block of 18 floors and 85.4 meters that was completed three years ago in Norway; or HAUT, a 73-meter building with 55 apartments located in the Netherlands.
Beyond the streets or architecture and engineering studios, the new trend is also being felt in the industry itself. Since 2014 — details The Wall Street Journal— 18 manufacturing plants have been built in the United States and Canada and forecasts show a considerable increase in demand: over the next few years, between 2021 and 2028, Grand View Research estimates that the world market for mass timber it will grow at an annual rate of approximately 13.6%.
The big question is: in addition to its curiosity, its aesthetic effect or to satisfy the unconditional planks, why do we build skyscrapers with wood when we have been doing it with concrete and steel for years? Why change if we have done well so far? Its defenders emphasize that it presents important advantages. The main, perhaps, its impact on the environment.
Some studies —collects The Wall Street Journal— conclude that the carbon footprint of a building built with mass wood harvested sustainably and selectively can be half that of another built with concrete and steel. Along the same lines, Think Wood assures that replacing steel with mass timber reduces carbon dioxide emissions between 15 and 20%. “According to some estimates, the short-term use of CLT and other emerging wood technologies in seven- to 15-story buildings could have the same emissions control effect as taking more than two million cars off the road for a year.” , he argues.
calculate how many carbon emissions generates wood en masse throughout its entire cycle, including felling, release of CO2 from the soil, machinery and transport, in addition to the carbon embedded in the wood itself, is not an easy task. Architect Michael Green claims that a single cubic meter of CLT wood “sequesters” a significant amount of CO2. Regarding the production of cement, concrete, steel and iron, it is estimated that the first two emit 8% of global greenhouse gas emissions and the remaining two close to 5%.
Manufacturers also point out the advantages of mass wood as a material. Think Wood specifically points out three: its resistance, strength and lightness and the saving of time and costs. According to the studies he manages, the buildings of mass timber they are considerably lighter —he is talking about a fifth— than those made of concrete, which would allow them to respond well to earthquakes. Fire resistance tests also show that a CLT wall with five-layer panels can withstand more than three hours at temperatures of more than 1,800º Fahrenheit, about 982ºC.
The third advantage that Think Wood points out is also key: cost and time savings. Unlike other materials, mass wood arrives prepared from the factory, where they use precision machines that help avoid discards and waste. The team at the Sara Cultural Center calculates, for example, that by manufacturing the panels and beams in a nearby factory, they saved a year in construction costs and labour. “Solid wood buildings are built about 25% faster than concrete buildings,” says Think Wood. Magazine vox It goes further and also points out that the characteristics of prefabricated parts require less labor.
In the “presentation sheet” of mass wood not all are strong points. The main concern generated by an increase in demand is that it could lead to exactly the opposite that those who defend its advantages for the environment are seeking: an exploitation of less protected forests without selective criteria. “There are objective limits to the amount of wood that we can produce and consume. We must take into account the limitations in which we must operate,” Jason Grant, of the World Wildlife Foundation, told The Wall Street Journal.
Some also believe that perhaps we are overestimating the benefits of wood for the environment and that when calculating its carbon footprint we should take into account factors such as the fossil fuels used during transport, felling and the manufacture of parts or the burning of roots, branches and other parts of the trunks. Another handicap is the relative novelty of the mass timberwhich perhaps deprives us of the experience we do have with steel or concrete.
What towers like the one in Skellefteå, Milwaukee and Brumunddal or those proposed for Tokyo, London or Berlin show is, in any case, that wood, one of the oldest building materials, is pushing hard to gain space in the architecture of the XXI.
Images | Booking, UTB, PLP Architecture and Moelven
George is Digismak’s reported cum editor with 13 years of experience in Journalism