TedEd: Could we build a wooden skyscraper?

By Stefan Al

Mjøstårnet is an 18 story tall building towering over the forests of Norway. But this isn't just any old building - it's the tallest wooden building on Earth. But even at the end of the 20th century, scientists believed a wooden building couldn't get over 6 levels. This is because regular lumber could handle forces parallel to its grain very well, but not forces perpendicular, meaning it couldn't withstand the weight of a tall building or the wind at high altitudes. However, the late 1800s brought about the creation of glue-laminated timber (glulam), and a century later, cross-laminated timber (CLT) was invented. In glulam, boards are stacked on top of each other and in CLT, layers are oriented opposite to each other. This meant glulam had significantly more tensile strength and CLT could withstand forces in both directions. These types of building materials can be made more easily than steel or concrete, and they are less likely to be permanently damaged in a fire. Additionally, they could help lower the 11% share that the construction industry has in global warming. Still, CLT and glulam are not as strong as steel and concrete, and require more wood than traditional construction. It's unlikely that they will be strong enough to support true 40-story skyscrapers, but even building up to 30-stories with a mix of steel and concrete could significantly lower our carbon footprint.