Architects, designers, and engineers are getting a bigger set of building blocks, all thanks to new technologies set to transform the way we build tall buildings—but we’re not talking about steel or concrete. Mass timber buildings are put together with much larger wooden structural components than traditional wood-framing or post-and-beam construction. Massive wood walls, floors, roofs, and stairways prefabricated in Oregon forests and sawmills will be vital in the evolution of future city skylines.
Teaching Old Materials New Tricks
In 1885, Chicago’s Home Insurance Building first used structural steel in a weight-bearing frame. It stood 138 feet tall, and had a third of the mass of similar masonry structures. Never much to look at, the Home Insurance Building was demolished in 1931. Celebrated as the world’s first skyscraper, it changed the way people thought about building in a profound way. Steel had effectively redefined our skyward boundaries.
That’s lovely, but if we look to the Sakyamuni Pagoda of Fogong Temple in China’s Shanxi province, we’ll see that it was more than slightly taller at 220 feet. Oh, and it just happened to be built completely out of wood… more than 800 years earlier, way back in in 1056. Despite centuries of strong earthquakes, there it stands today.
Point being, nature figured out how to reach for the skies long before humans ever gave it a go. Trees were achieving those heights standing on one leg well over 100 million years ago. While concrete and steel will continue to be the dominant forces in tall buildings, the progression of building technology will provide lessons from nature that not only promise new form, but multiple scales of function.
The production of concrete and steel accounts for about 8% of global CO2 emissions. However, wood is a bit different. Since trees spend their lives pulling CO2 from the atmosphere, wood makes a decent solid carbon storage system. The fewer steps between a tree and its new life as a building material, the more efficient the storage. Skyscrapers built with new precision-machined wood panels offer a much smaller carbon footprint than traditional methods. In terms of energy and waste, wood building components are cheaper and cleaner to produce.
Now, picture a piece of plywood: thin sheets of wood stacked and pressed together. The grain of each layer is perpendicular to layers above or below it. This cross-directional pattern results in a relatively strong and dimensionally stable building material. In the 1990s, European manufacturers started experimenting with much larger cross-laminated timber, called CLT panels.
CLT scales up this cross-grained idea. Panels are made with regular dimensional lumber like two-by-fours already produced by sawmills. Three to nine usually perpendicular layers of lumber are tightly stacked and pressed into big panels. They’re similar in cross section to a fresh game of Jenga—instead of a three-inch square toy tower, CLT panels become 30-foot floor sections, or five-story wall components. Panels are limited by the size of the press, and what can fit on a truck. Most panels measure less than 35 feet, but some are up to 65 feet long.
Panels can be precision machined into enough shapes and sizes to make Ikea and Lego enthusiasts salivate. Imagine passing a flat-packed building on the road into town. Yes, it looks exactly like that lovely coffee table and bookshelf new in the box. Adopted into the International Building Code last year, use of this technology is catching on worldwide.
Corvallis’ Role in Building the Future
The first building-wide structural use of CLT panels in the United States, Albina Yard is a four-story, 16,000-square-foot North Portland office constructed earlier this year. The building’s CLT roof, floors, and glue laminated timber frame were produced by D.R. Johnson Lumber Co. over in Riddle. There’s another neat fact; they’re the only domestic producer of certified structural CLT panels in the United States, right here in Oregon.
Using traditional construction methods, the first 4,000-square-foot layer of floor would have taken more than a week to complete. The first layer of CLT panels was installed in less than four hours. Windows, doors, air ducts, service access, stairs, and elevator shafts can be precision machined off-site. These new technologies could save construction schedules months, not to mention the reduction in noise and construction traffic.
Albina Yard’s designers, Lever Architecture, will be constructing a much larger project next: a 12-story mixed residential/commercial project called “Framework” in Portland’s Pearl District. The project was one of two winners awarded $1.5 million in the U.S. Department of Agriculture’s U.S. Tall Wood Building Prize Competition. According to Lever Architecture, “The USDA grant will allow the project to engage the exploratory phase, including the research and development necessary to utilize cross-laminated timber (CLT) and other engineered wood products in high-rise construction in the United States.” The building will be one of the first tall timber structures in the country.
Corvallis itself stands poised to become the U.S. hub for developing CLT technology. Oregon State University’s College of Forestry’s Wood Science & Engineering department researchers and associated partnerships are providing the data to confidently design, build, and certify these types of mass timber buildings. The College of Forestry’s own new buildings will feature a variety of mass timber construction technologies, including CLT. Someday soon, temporary structures designed and built in student competitions could add to the growing library of different solutions in this fledgling industry.
Forest resources have long been part of this state’s industry and culture. Mass timber construction could provide a new link between rural and urban communities along with an entirely new supply chain of job opportunities, including laminators, machine operators, specialty contractors, as well as connector hardware and equipment manufacturers.
CLT manufacturing could help revitalize natural resource-oriented rural communities, and a future CLT industry may provide opportunities for the sale of previously less marketable timber resources, such as beetle-killed lumber and smaller diameter logs. This could help fund future forest restoration efforts and help land managers create healthier landscapes.
Responding Well to Criticism
Historically, fire concerns have been the principal reason for limiting wood buildings to four stories or less. These concerns have rightfully been expressed towards mass timber construction as well, but physics is reassuring. Traditional wood framing has a much higher air-to-fuel ratio than solid slabs of wood. Want a larger fire, don’t bother with big logs; go get some pallets!
Researchers suggests mass timber elements not only burn steadily and predictably, but continue to perform very well in terms of structural integrity, even after hefty mass losses. Wood Science & Engineering researchers are currently testing fire performance of locally produced CLT wall and floor assemblies. Fire behavior will pretty definitely be a major aspect of testing for any future mass timber products.
There are many other questions clamoring for answers. The development of effective performance models is highly dependent on issues of serviceability, durability, thermal comfort, and other factors. And of course there’s still that pesky earthquake issue.
As we have been constantly reminded by our tin-foil hats, a Cascadia subduction zone or some other earthquake is certain to be along directly. Proven seismic performance, and high strength-to-weight ratios of CLT and other mass timber building methods make them very attractive options for new construction.
The 1995 Kobe earthquake measured 6.9 on the moment magnitude scale. European researchers and CLT manufacturers used the tri-axial record of that event as input in an earthquake shake table test on a seven-story CLT building in 2007.
CLT panels for this structure were made in Italy and shipped to Miki City near Kobe, Japan. The 76-foot-tall building was assembled in just over a week, and after simulating several severe earthquakes, the structure survived with no residual deformations other than a few bent screws. The entire thing was then disassembled and shipped back to Italy to be reused.
CLT Just Crawling Into the Future? Not for Long
Despite growing interest in the U.S. and abroad, practical adoptions of these new building techniques are only growing about as fast as the trees. We stand at an audacious chicken-or-the-egg moment in time—while architects and investors are enamored with the speed and efficiency of CLT construction, production is limited. This creates a bottleneck for orders, and in turn perpetuates the production issues.
If 5% of new construction under 10 stories in the U.S. used CLT technology, the material alone would be worth an estimated $1.4 billion annually. The same scenario indicates a market opportunity for 0.9 billion board feet of timber volume. This would represent more than triple the estimated global CLT production capacity in 2013 (estimates based on the 2013 CLT Handbook: US edition).
Given the efficacy of mass timber materials and this sort of market potential, it is unlikely that things will be inching along forever. And when the dam bursts, we’ll likely be at ground zero for the next mass evolution in skyward construction.
By Matthew Hunt