The University of Toronto is constructing a 14-storey mass timber building, one of the largest and most recent projects using this innovative construction technology. “Mass wood is an attractive alternative to energy-intensive concrete and steel, which together account for nearly 15% of global carbon dioxide emissions,” Knowable Magazine reports. “Although experts are still debating the role of mass timber in combating climate change, many are betting that it is better for the environment than current construction approaches. After all, it is based on wood, a renewable resource.”
Today, the tallest mass timber building is the 25-story Ascent skyscraper in Milwaukee, completed in 2022. As of that year, there were 84 mass timber buildings eight stories or more built or under construction overall the world, with another 55 proposed. Seventy percent of existing and future buildings are located in Europe, about 20 percent in North America and the rest in Australia and Asia, according to a report by the Council on Tall Buildings and Urban Habitat. If smaller buildings are included, at least 1,700 mass timber buildings were constructed in the United States alone in 2023.
In principle, solid wood is like plywood, but on a much larger scale: smaller pieces are layered and glued together in large, specialized presses. Today, beams up to 50 meters long, usually made of what is called laminated wood can replace steel elements. Panels up to 50 centimeters thick, typically cross-laminated timber, or CLT, replace concrete for walls and floors. These wood composites can be surprisingly durable, stronger than steel by weight. But a solid wood element must be bulkier to achieve the same strength. As a building gets taller, the wood supports must get thicker; At some point, they simply take up too much space. Thus, for taller mass timber buildings, including the Ascent skyscraper, architects often turn to a combination of wood, steel and concrete.