When the first skyscrapers began to appear in Chicago and other American cities at the beginning of the 20th century, they were a marvel of modern technology. Innovations in the production of steel beams and elevators have allowed buildings to soar ever higher, culminating in amazing structures like the Burj Khalifa in Dubai, which stands at 2,717 feet.
In the very near future, we may increasingly see our cities full of skyscrapers built using new technology, but a very old material that steel has replaced: wood.
Sound impossible? Keep reading to hear about how composites created from this traditional material are creating a revolution in the construction of tall buildings.
People have been building out of wood for a long time and history has known some pretty tall structures made from this material. The Yongning Pagoda, in ancient China, was possibly as tall as nine stories. More recently, Germany built a radio transmission tower in the early 1930s that was 623 feet tall — the tallest wooden structure ever built.
But here we’re interested in skyscrapers — large structures of multiple floors that can contain residential and/or retail space. The first buildings to earn that name were 10 stories or higher (though buildings now need to be quite a bit taller to officially count as skyscrapers).
Still, by any measure, a 10-story building is pretty tall and, until recently, would never be made out of wood. For that reason, it is remarkable that Milwaukee now has an all-wood building under construction that will reach a height of 25 stories and 284 feet when finished.
This is by no means an isolated example; such structures are being planned and built all over the world. How did we get here?
Two key factors have led to the sudden rise of wood as the material of choice for tall buildings.
The first is technological. The wood used to construct these buildings is made of highly engineered composite materials.
One of the newest of these is cross-laminated timber, developed in Europe in the 1990s. It consists of strips of dimensional lumber glued together in layers oriented at 90 degrees to each other. It looks a bit like layers of butcher block sandwiched together.
This configuration provides incredible strength and prevents the warping and twisting common in standard dimensional lumber. Cross-laminated timber is typically produced in panels ranging from 2 to 10 feet in width, with a thickness of up to 20 inches, and in lengths as much as 60 feet (or even more).
Two other composite wood products have also been important. One is glulam, which is essentially a stack of dimensional lumber glued together with the grain all running in the same direction. Another is laminated veneer lumber (LVL), which is essentially thick plywood used to form structural elements.
With the necessary technology in place, growing concern about environmental impact and sustainability created the right conditions for trying something new. Since wood is a renewable resource, engineers and architects began to consider using wood composites as an alternative to the more traditional building materials, steel and concrete.
The first attempt to actually do so at the scale of a large residential building was built in London in 2009. The Stadthaus is a 9-story structure that was the first of its height to have its load-bearing walls, floor slabs, stairwells, and even elevator shafts made entirely of engineered wood.
This was followed by a similar project in Australia and, soon after, by buildings in Canada, the United States, and other European countries. Some significant recent examples include Mjøstårnet in Norway (2019) and the HoHo in Vienna (2020).
It is fascinating to discover that we have figured out ways to build skyscrapers out of wood. A natural question, though, is why we’d want to. Why not just stick with steel and concrete?
One reason we already mentioned is environmental. Not only is wood a renewable resource, but its use in construction has a much lighter environmental impact. The production of both concrete and steel is very energy-intensive and generates significant carbon emissions. It is estimated that about 13% of the world’s total carbon emissions come from the production of these two materials.
In comparison, it takes little energy to manufacture wood composites. Moreover, trees capture a large amount of carbon as they grow.
Another reason is efficiency. Engineered wood components are easier to fabricate, lighter to haul, and can be assembled more quickly on site. The Brock Commons Tallwood House, an 18-story wooden skyscraper in Canada, was erected in just 70 days. This means significant savings on transportation and labor costs.
Finally, wood is aesthetically pleasing and may even affect us physiologically. One study found that students in a wood-paneled classroom were more relaxed and slept better than those in classrooms with other materials.
Those at the forefront of wooden skyscraper construction recognize that one of the challenges is public perception. For many people, the idea of a wooden skyscraper just doesn’t sound safe.
The main reason for this is a concern about fire. Being several floors up in a wooden building when a fire breaks out isn’t an appealing prospect.
The reality is, though, that engineered wood may be even safer than steel in the presence of fire. The treated composite products used in wooden skyscrapers are highly fire-resistant. When they come into contact with fire, they form a layer of charring on the outside that insulates and protects the interior from further damage. Moreover, steel is subject to sudden failure in the presence of intense heat in a way that wood is not.
Will this new way of building catch on? We think it is an exciting innovation, but we won’t pretend to predict the future. One company in Japan has announced plans to build a wooden skyscraper 1,150 feet tall, to be completed in 2041. We’ll see.
One thing we expect is that the wooden composites used in construction will become increasingly sophisticated and continue to improve. One way this will happen is by incorporating other reinforcing materials to enhance the capabilities of wood and glue alone.
A recent example is a process developed for pultruding thin layers of reinforcing fibers embedded in a thermoset resin matrix. These layers, when combined with the wood layers in laminated products like glulam beams, yield a product with even greater strength.
If these wooden buildings continue to grow taller, they will need to use composites like this to handle increased stresses from wind and earthquakes.
We get excited about what pultruded composites can accomplish because we see them every day. We help our customers discover innovative ways to solve their design challenges with pultruded fiberglass. If you’d like to have a conversation about how we can help you, get in touch today.