Going up! The rise of the wooden skyscraper

Image: Michael Green CC

Image: Michael Green CC

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Two years ago, October 2014, the U.S government (in partnership with the Softwood Lumber Board and the Binational Softwood Lumber Council), announced the U.S. Tall Wood Building Prize Competition. "Wood may be one of the world's oldest building materials, but it is now also one of the most advanced," said Secretary Vilsack. Canadian architect Michael Green says (see video below) that "Wood is the most technologically advanced material I can build with. It just happens to be that Mother Nature owns the patent." 

And now wooden buildings and even skyscrapers are beginning to crop up. In Vancouver a student residence, 18 storeys tall, and made of wood, will be completed in 2017. Rules in BC about wooden structures have been relaxed over the last few years. This month, in Vienna, Austria, construction began on what is planned to be the world's tallest wooden skyscraper at 24 floors (84 meters)

However, this is not the log cabin approach. What builders and designers are using in general is Cross Laminated Timber (CLT). As the Softwood Lumber Board explains "Cross-laminated timber (CLT) is a wood panel typically consisting of three, five, or seven layers of dimension lumber oriented at right angles to one another and then glued to form structural panels with exceptional strength, dimensional stability, and rigidity."

There are a few reasons provinces like British Columbia and the U.S. government have been pushing wooden buildings. One is the lost of forests to pests. Millions and millions of trees have been wiped out by the Mountain Pine Beetle. If the wood is burnt or used left to rot, the Co2 is released to the atmosphere. Instead, if portions of the trees can be used for construction the GHG are sequestered and provide a commercial use. Some versions of CLT use young trees that can be farmed and applied quickly into mass timber panels (again see video below).

As Lloyd Alter in Tree Hugger reported a few years ago "[CLT] replaces concrete, which is responsible for as much as 5% of the world's CO2 and the excavation of mountains worth of aggregate. It is fast flatpack design and construction; . . .  This three storey showroom at the XTLEXPO in Milan was assembled by two men in ten hours."

CLT is very strong (similar to steel) and is 25% of the weight of concrete. But what about fire? Most Canadians live in wooden buildings already but a wooden skyscraper is a different thing (and so is CLT). Architect Michael Green spoke to CBC about fire and wooden buildings:

"It is always the first question and with any building you have to worry about fire, and of course with a wood building there are some special conditions that we work with. And so the analogy I often use is, little pieces of wood catch fire, big pieces of wood are very difficult to catch fire. So we all know that in our fireplace. Little sticks will start a fire, but if you tried to light a big log, it will never catch, or it will be very hard to catch. And so the premise is we use huge-scale wood that resists fire naturally and burns very predictably in a very similar way to control a fire as it would be in a steel or a concrete building."

"What we do with all the buildings is we cover them in a envelope. So it's a lot like, if you think about our bodies, we are a skeleton. Building structure is what we're talking about, it's the skeleton, and we cover up in layers that protect our skeleton and we do the same in buildings to prevent them from weathering conditions and insects and so forth. So, we always protect the structure from that."

If we are going to meet our GHG goals we need to build better and smarter. Building taller buildings from wood to account for more dense housing has real potential. Of course it also has dangers, such as under-regulated, under-supervised forestry practices in parts of the world. For now though, the future of wood buildings is high. For more reading see Michael Green's report "The Case for Tall Wooden Buildings" (PDF).