A novel kind of plywood is poised to revolutionize the construction industry.
They just don’t make ’em like the Sakyamuni Pagoda anymore. Built from wood in 1056 in the Shanxi province of China, the building has remained standing to this day, despite seven earthquakes rattling the region within its first 50 years of existence. Since then, it’s held up against a slew of seismic events, even when more-modern structures have failed. Now, thanks to recent advancements in timber technology, modern architects are rediscovering the benefits of working with wood.
Wood was the go-to construction material from the dawn of time up until the late 19th century. However, it is far from ideal. For one thing, its cells can swell and shrink by up to 10 percent of their original size, depending on the humidity. Plus, if it stays wet for too long, the material rots. Imperfections in the grain weaken its structural integrity and can cause it to fail under loads that it should otherwise support. In its natural state, wood breaks more easily than steel and bends more readily than concrete. Wood’s biggest drawback is, of course, the fact that it burns so readily. That’s not what you want in a densely packed urban center, as the fires of San Francisco in 1851 and 1906, Chicago in 1871, and Boston in 1872 illustrate.
Still, while the 20th-century skylines were dominated by steel and concrete, the first two decades of the 21st have seen a rapid influx of wooden architectural designs. However, many are still little more than artist renderings. In 2012, the 10-story Forte residential block in Melbourne, Australia, became the world’s tallest timber building. It was quickly overtaken two years (and four stories) later when The Treet in Central Bergen, Norway, was completed.
The Brock Commons, in Canada, currently serves as 18 levels of student housing for the University of British Columbia. And by the end of this year, architects in Portland, Oregon, will break ground on a 12-story mixed-use structure dubbed the Framework, which will be the tallest wooden building in the US once it’s complete. It should be complete by 2019. That structure may not hold the title for long, however, as the Cambridge University Department of Architecture is looking at how it might construct twin 80-story residential towers — one on the Chicago River, the other in London.
This rapid proliferation of designs is all thanks to a kind of building material called cross-laminated timber (CLT), which was invented in Europe in the 1990s. It’s not that different from plywood, actually, just produced on a much larger scale. Long planks of two-by-fours are glued together side by side into sheets. Those sheets are then stacked three or four layers high, separated by fire-resistant glue and pressed together. By rotating the grain of each subsequent layer by 90 degrees, the composite material shows a structural strength that rivals steel and negates the imperfections that any one layer might have.