A handful of architects want wood to usurp concrete and steel as the key material for building skyscrapers. From Vienna’s HoHo tower to Stockholm’s Trätoppen and Minneapolis’s 18-story T3 project, wooden skyscrapers are being constructed as a way to make building quicker and more environmentally friendly.
Wooden skyscrapers have speed on their side, as they don’t require concrete floors, which can take weeks to dry. And they offer an environmental advantage. Experts believe concrete and steel buildings create about 8 percent and 5 percent of global emissions respectively. Trees, however, absorb CO2 and lock it away from the atmosphere.
The most obvious drawback would seem to be wood’s flammability. Indeed, the use of timber-frame blocks in construction has come under increasing scrutiny in recent years, with some experts in fire protection claiming that any type of wood in a structure raises concerns, and is dangerously vulnerable.
However, the new timber that architects are excited about is quite different from straight-up wood. First developed and used in the 1990s, cross-laminated timber (CLT) is comprised of small pieces of wood criss-crossed together and set with fire-resistant glue. Supposedly as strong as structural steel, and sometimes described in the industry as “plywood on steroids,” CLT’s unique composite allows architects to build with timber at heights previously deemed impossible.
CLT can be used to make huge pieces of timber, and even entire walls. “If you’re making a fire, everyone knows you don’t start with giant logs,” Anthony Thistleton, a founding director of Waugh Thistleton Architects, told the BBC in October 2017. “It would take a lot to ignite them.” Plus, unlike concrete and steel, it will not melt under extreme heats.
Natural wood isn’t the only environmentally friendly alternative to concrete and steel. Scientists at University of Science and Technology of China in Hefei recently created a “synthetic wood” that’s as strong as natural wood but is less vulnerable to fire and water.
The new material is a freeze-dried solution that includes sugar polymer derived from the shells of shrimp and crabs; the material is heated to temperatures as high as 200 degrees Celsius, forging strong chemical bonds. As a result, the material has increased strength, and is largely resistant to water and acid.
There are, however, safety concerns around using wood and wood alternatives in construction. Wind speeds increase at higher levels, and so the taller the wooden building, the less secure it will be.
There are also concerns over the ability of natural wood and synthetic wood buildings to withstand earthquakes. According to Shiling Pei, an assistant professor at the Colorado School of Mines, the seismic performance of CLT is still “unchartered waters.” However, tests conducted in 2017 have given researchers, including Pei, reason to be optimistic.
In 2017, a two-story wooden structure endured four different earthquake simulations on the world's largest earthquake simulator in San Diego. The ultimate aim of these tests is to determine whether wooden buildings as tall as 20-stories could survive large earthquakes.
As concerns over C02 emissions and their impact on the climate rise, more and more environmentally friendly alternatives are being put forth, and the construction industry is one of many seemingly on the verge of transformation. As Anthony Thistleton says, “The 20th century was the concrete age, it was all about the dominion of man over nature. Now we’re transitioning towards a different attitude, a more nurturing one.”