This article was originally published on Common Edge.
Chinese temples have stood for centuries, battered by wind and earthquakes, without a crack or timber out of place. They employ an ancient technique called “bracket set construction” that requires no nails or metal parts to connect wooden structural elements. Scandinavian stave churches are nearly as durable. Unsurprisingly, there are plenty of trees in Sweden and all over China.
So what is with the hype about innovation in “mass timber” construction over the past few years? As Boyce Thompson argues in his thoughtful new book, Innovations in Mass Timber: Sequestering Carbon with Style in Commercial Buildings (Schiffer Publishing), this will be the next big thing in “green” tech for architects feeling guilty about their costly titanium skins and outsized carbon footprints. The color photos show some impressive buildings in places where the wood industry has always been healthy, such as the Pacific Northwest and Scandinavia. The Japanese build log cabins with imported material that might as well be gold.
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One project immediately stands out. Shigeru Ban, a Pritzker Prize–winning architect who builds with paper tubes when they can meet a tight budget, has given the Swatch watch company a zany headquarters made with large glulam timbers in a tube-like configuration that makes a translucent roof over concrete-frame offices. Since the majority of the construction appears to be conventionally non sustainable, are we looking at “greenwashing” here? (Just asking.)
Like many false claims that there is promise in “green high-tech,” the mass timber craze is exciting until one realizes that gimmicks are designed to hide larger economic and policy problems that must be fixed before we can get to our net-zero utopia. As an architect who has restored heavy-timber buildings and built with traditional framing for decades, I am already a believer. You can’t do better than Three Little Pigs construction. As Steve Mouzon argues on his Original Green website, traditional design is sustainable by definition.
So adding a few new glued-up products to a catalog that already included large-section composite timber elements is a great thing. Mass timber technology has been around for more than a century in countries where wood has been plentiful. Alvar Aalto used many different types of “high tech” timber structure in his buildings from the 1930s. Paul Hayden Kirk did the same in buildings around Seattle in the 1950s and 1960s. As the size of trees harvested in these areas shrank, manufacturers were forced to find ways to create large timbers from smaller, thinner ones by attaching them together. The first glues used formaldehyde and caused health problems. Today we have better alternatives, but strong adhesives are key.
The two new kids on the block are panels and large chip-formed beam-column assemblies. Bent-wood laminated frames have always been an option for medium-span structures like churches. Before we get into their innovations, though, we must address the elephant in the coliseum: modern building codes.
Contemporary engineers and code officials are afraid of wood. They have some legitimate concerns about a material that is generally ubiquitous in wet and temperate climates. For centuries, wood buildings provided fuel for massive, terrifying fires in cities and countrysides. (Think Mrs. O’Leary’s cow.) Wood buildings made of “stick construction” burn quickly. Massive timbers do not, but in olden times there were no fire companies on hand to quench blazes within a few hours. Believe it or not, our fire codes are based on case studies from the early 20th century and prohibit or discourage wood construction for most public assembly building types, as well as multistory housing.
In addition, wood beams are relatively weak in bending compared with steel, so that maximum spans are less than half of what is expected of steel wide-flange or J-joist beams. If one is designing a high- or medium-rise building in a city, one wants 20 feet or more for economy and flexibility. And engineers today are not trained to work with wood-to-wood or wood-to-steel connections when simpler methods, using steel or reinforced concrete, are already modeled in their software. They look at their computers and are discouraged from going out on a limb (sorry) to specify wood structural components. In my experience, many simply refuse to work on wood buildings, even historic ones.
Enter the new large-section beams and wood columns that are manufactured from small strips or chips of ubiquitous timber species. Without the need to mill 3- or 4-inch-deep strips of fir, spruce, or pine to create conventional glulam sections, companies have been free to use smaller pieces in large sections that can be heat pressed together with less glue. The economy has resulted in competitive prices, compared with steel or concrete construction. Though experts disagree on whether mass timber is cheaper, the industry is pressing hard for code changes that will allow it to compete on a level playing field.
There are really two game-changing products out there that clever architects are using with panache. Cross-laminated timber (CLT) panels are formed by laminating strips of wood perpendicular to each other in succeeding layers. Many builders use laminated veneer lumber (LVL) joists in house framing; you can find it at Home Depot. The confusing new variety is laminated strand (LS) lumber, and it isn’t made from veneers. Oriented-strand board (OSB) is its closest cousin, as both use wood chips that are often scraps from a lumber mill, for their raw material. That means weaker sections, so you can’t make this work in long spans. However, one can use larger beams and columns in wood assemblies because they resist flames when there is more wood to burn, and because they weigh less than concrete. They also tend to look handsome when finished. CLT can be both structural and non-load-bearing, as when it is used in ceilings.
What many leading-edge architects are banking on is that the whole range of timber products may be supercharged with new fabrication and construction methods to give new life to an old industry. It turns out that timber is lighter and faster to erect than either steel or concrete, saving valuable labor time and shipping costs. What about those difficult timber joints? New technologies make fabrication easier with CNC machines so that mortise and tenons can be cut in seconds. Though many connections still require metal plates and brackets, they are less obtrusive than the large iron gussets seen in many old factory buildings. Cranes used in steel buildings can lift and manipulate large timber beams and columns with ease.
Thompson’s book documents a wide range of interesting projects with enough detail to whet one’s appetite for more. He doesn’t sugar coat the problems I’ve highlighted here, but gives examples of new building codes that are working their way toward approval in both the U.S. and Europe. The issue of moisture on building sites is also mentioned, with the caveat that even laminated timbers shrink and expand enough to cause headaches for builders. But don’t confuse this book with a technical manual, as the data is sprinkled throughout the case studies and isn’t comprehensive.
The projects I found most exciting were those that used timber in ways that only timber may be used. Eight-to-12-story apartments or office towers with grids that could be concrete don’t impress me, but composites of wood and glass, such as the Hans Christian Andersen Museum (Denmark) and Sara Kulturhus (Sweden) are dazzling. It appears that the Seattle architect Susan Jones is a pioneer with two projects in the book, one in my home town of Bellevue, on the east side of Lake Washington. She had to work with both code and fire officials to get her buildings approved, but found them open to some ingenious hacks.
One gigantic project that can’t be assessed because of its hybrid construction was built recently in Australia. The architects weren’t picky about mixing materials, metaphors, and design motifs, so Bunjil Place pleases everyone by giving them choices: if you don’t like one facade or space, walk a thousand yards and you will see something different. The extraordinarily complex eagle-leg timber structure at the main entrance is purely decorative, as the architects had to use steel and concrete for most of the swooping, winglike roofs. The only other timber elements in the vast multiuse complex were the wall panels, which have a wood core but metal and gypsum board on the exterior and interior surfaces. The building is a marvel, but don’t call it mass timber.
Let’s be clear: Anything built of wood is sustainable and reduces our collective carbon footprint. Trees are nature’s best carbon-sequestering machines. They can be grown sustainably or cut for profit and wasted. The global timber industry has hardly behaved like a good citizen for most of the last century. If it is being forced to play well with others, that is a benefit to the building industry. Adding new products, and giving architects good reasons to employ them, is something I applaud. But we can still build with sticks, trusses, and roof trees, as we have for millennia. A 200-year-old white oak is as massive as anything made in a factory today—if you can find one.
