To many, the idea of a 30-story skyscraper made of wood is ludicrous. Such a building would be a match strike away from becoming a towering inferno and about as structurally sound as a Jenga tower, right? If you are envisioning a massive tower constructed of two-by-four framing like many stick-built homes you are probably correct. Of course these wooden skyscrapers, or “woodscrapers”, are being built using a building material stronger and more technologically advanced than your standard two-by-fours. Mass timber is a term used to describe a number of large engineered wood products that typically involve the lamination and compression of multiple layers to create solid panels of wood. Examples of mass timber include cross laminated timber, laminated strand lumber, laminated veneer lumber and glue-laminated timber.
Advocates of mass timber claim a number of benefits of its use over traditional steel and concrete for constructing tall buildings. If the timber is sourced responsibly it provides a completely sustainable and renewable building material. Carbon emissions from manufacturing mass timber products are a fraction of those created by the production of steel and concrete building materials. The production of steel and concrete products account for about 8 percent of global greenhouse gas emissions annually. By using lumber all of the CO2 absorbed during photosynthesis of the tree’s life remain trapped in the building product when using mass timber instead of creating more when using steel or concrete.
Mass timber has a natural tendency to char in a fire which slows the burning process and helps maintain structural integrity. The same thing happens when you throw a whole log on a fire and it takes forever to burn which is part of the reason people split their firewood. Mass timber’s resistance to fire can be further improved by encapsulating mass timber in gypsum board. Tests have shown that cross laminated timber can achieve a fire rating of three hours.
Regular milled lumber is nowhere near as strong as steel and concrete whereas mass timber products have been proven to be as strong as or stronger than both steel and concrete. Mass timber products are also considerably lighter than concrete. The thermal performance of mass timber is also far superior to its steel and concrete counterparts which means lower heating and cooling costs.
Wooden skyscrapers are still in their infancy. Consider the Home Insurance Building built in 1884. It is considered the world’s first skyscraper and the first building to use structural steel in its frame and was only 10 stories tall. Wooden skyscrapers are currently at the same developmental stage that steel skyscrapers were at back at the turn of the 20th century. Current wooden skyscrapers are topping out at around 10 stories like the 10-story Forte Building in Melbourne, the 9-story Stadthaus in London and the 8-story H8 in Bad Aibling, Germany. And much in the same say that steel skyscrapers got progressively taller and taller there are already plans for taller and taller wooden skyscrapers.
Architect Michael Green has proposed and designed a 30-story wooden tower in Vancouver as well as designing the much smaller Wood Innovation Design Centre currently under construction. CF Møller has designed a 34-story wooden skyscraper that could eventually be built in Sweden and Michael Charters conceptualized the 40+ story Big Wood project in Chicago. The CF Møller project and the Big Wood project were both part of separate design competitions.
Now I don’t think we’ll ever see a wooden skyscraper that will rival the likes of the Burj Khalifa in Dubai which currently holds the title of world’s tallest skyscraper at 2,722 feet and 163 stories but I do think that one day wooden skyscrapers will command a large market in the future. This is provided that wooden buildings can be proven to be a viable alternative at 40 stories or more. Wooden skyscrapers and mass timber could be the ultimate eco-friendly alternative to their concrete and steel counterparts.