Centuries-old, this green building material is just now gaining steam. Will it help mitigate climate change or add more wood to the fire?
Environmentalism is awash with buzzwords: Biodegradable. Carbon footprint. Carbon neutral. Eco-friendly. Emissions. Global warming. Greenhouse gases. Pollution. Recyclable. Renewable. Sequestration. Sustainable. Zero waste. They are everywhere—in our social media feeds, newspapers, magazines, television, and radio. Used so frequently, they’ve become part of the background noise as we complete daily tasks.
Despite this fact, I still stumble across new words in my research. Mass timber is a recent one. What is it? Engineered wood designed to be nearly as strong as concrete and steel. Its strength comes from layering—layers of wood stacked either parallel or perpendicular to one other. And depending on the desired end product, these layers are held together with glue, nails, or dowels and structured as beams or panels.
About three decades old, this European-based technology is only now beginning to turn heads in North America thanks to architectural pioneers like Michael Green, whose 2013 TED Talk and Vancouver-based architectural firm tout its benefits. Listed among those benefits are eco-friendly and sustainability. Is this hype, reality, or a mixture of both? Let’s see for ourselves.
A not-so-new technology
The first wooden structures were probably lean-tos, with armfuls of branches and twigs piled against wind-toppled trees. As our tools became more substantial and sharper, our construction methods advanced in kind, with timber homes cropping up about 10,000 years ago. As civilizations advanced, so did their structures, like longhouses, fortifications, churches, palaces, harbors, and docks.
Although most of that construction employed felled logs, builders found ways to cleave planks from those logs and, in time, shave those planks into ever-thinner sheets. Several of those sheets were glued together at some point, forming an early kind of plywood. Bits of laminated wood have been found in Egyptian tombs, and about a thousand years ago, Chinese artisans began employing it in their furniture. Hundreds of years later, in 1865, plywood was officially patented, but its popularity didn’t take off until the 1905 World’s Fair in Portland, Oregon.
Glue-laminated timber (glulam or GLT) appeared in France in the 1820s. It consists of pieces of sawed lumber that are stacked, glued, and pressed to form columns several inches thick or arches dozens of feet long. Though simple in design, it resulted in new ways to build ceilings and arches. The oldest known examples of its use are in two churches in Northumberland, England, built in the 1840s. Two decades later, in 1866, the assembly hall at King Edward VI College was outfitted with a glulam roofing structure.
At about the same time, nail-laminated timber (NLT) came into the picture. Initially calling it heavy timber or mill decking, builders nailed stacked pieces of lumber to form walls, floors, and ceilings for warehouses and factories. Inexpensive and easy to make, NLT soon became the go-to building material until early the next century, when devastating fires in several US cities forced building codes to favor less combustible materials, like concrete and steel.
In the 1990s Austrian and German designers began tinkering with cross-laminated timber (CLT)—layers of wood stacked perpendicular to one another. The designers soon discovered that CLT offered tremendous flexibility and strength, especially as a panel. Fashioned out of conifers and deciduous trees, like ash, beech, fir, and spruce, these panels can be as large as 20 feet long by 100 feet wide, though they are typically half that size for ease of transport.
Meanwhile, Swiss builders replaced the nails and glue in NLT with dowels and ended up with dowel-laminated timber (DWT). Made from softwood lumber that’s friction-fit together, DWT doesn’t need glue, making it greener than other types of mass timber.
A greener building material
So how exactly is mass timber eco-friendly and sustainable? Most materials used in construction are nonrenewable. Steel requires iron ore, which comes from massive open-pit mines. Cement (an ingredient in concrete) calls for limestone, which comes from quarries and open-pit mines. Glass needs pure silica (aka sand—also a prime ingredient in concrete). Aluminum is commonly found in bauxite, a shallow-forming mineral bulldozed from the earth in open-cut and strip mines.
Wood, however, is renewable. If done sustainably, this means harvesting mature trees and planting seedlings in their stead.
Wood is a carbon sink. From seed to harvest, trees grow by absorbing carbon dioxide from the air and combining it with water, soil nutrients, and sunlight to produce their food. With the help of chlorophyll (the chemical that makes plants green), these elements photosynthesize into carbohydrates and oxygen; the carbs feed the trees, and the oxygen returns to the atmosphere. And wood fibers greedily hold onto any uneaten carbon, which there always is—about half of wood’s dry weight is carbon. One cubic meter of CLT sequesters about a ton of carbon. What’s more, carbon can be locked away for a long time, like in the Horyu-ji temple in Japan, built in 607 AD, believed to be the oldest wooden structure in the world.
Wood is less carbon-intensive. Trees absorb carbon while alive, but decomposition frees some of it after they die. More carbon is lost due to forestry practices, but how much needs to be better understood? To gain a better idea, the Center for Sustainable Economy (CES), an environmental think tank, decided to examine how the forest industry impacts North Carolina’s forests and their carbon cycle.
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To do this, CES researchers accounted for the decay and combustion from logging residuals (dead roots, stumps, and waste logs) and the carbon emissions from industrial forest fertilizers, herbicides, and pesticides. They also examined historical logging data to determine annual clear-cutting rates. They conclude that about 201,000 acres of North Carolina forestland are clear-cut annually, resulting in 44 million metric tons of carbon dioxide emissions. Despite being carbon neutral, forestry tops out as the third-most carbon-intensive industry in the state, behind utilities and transportation.
Discouragingly, the CES further notes, “North Carolina’s industrial forestlands store far less carbon than the native forests they have replaced. On intensively managed timberlands and tree plantations, the amount stored has been reduced by roughly 50%.... In addition, for ten to fifteen years after a forest is clearcut, the CO2 released by the decay and burning of logging slash is greater than the CO2 uptake by newly established trees and vegetation. As such, clearcut lands are not only carbon sequestration dead zones but net emissions sources for long after they are logged.”
Worldwide, deforestation accounts for 10 percent of global carbon emissions. In comparison, the concrete industry claims 8 percent and the steel industry 5 percent.
More benefits
Okay, so mass timber is likely more carbon-intensive than advertised. Nevertheless, it still offers benefits that make it a noteworthy building material.
Holds up well against fire. Tested multiple times by the US Forest Service and the International Code Council, CLT holds up well against fire. The outer layers catch fire, but that burning wood soon becomes char, which insulates the interior wood from further damage. But everything has a fail point, and mass timber is no exception. It will eventually succumb to fire—after one or more hours. The same goes for steel, which can twist or buckle in high heat.
Shortens construction times. Labor and fabrication mainly occur at the factory, where computer numerical control machines make precision cuts. By accounting for every window, door, and vent opening, framing is built around the spaces, creating less waste. It can also be shipped to construction sites on a just-in-time basis, minimizing the volume of building materials stored on-site and traffic transporting those materials. Mass timber structures are generally 25 percent faster to construct, and the columns, beams, and panels making up those structures are a fifth of the weight of concrete and steel. Lighter buildings mean smaller concrete foundations, which means less concrete overall. Their lightness makes them suitable for brownfield development projects.
Responds well to earthquakes. Rigid and resistant to bending, concrete structures will crack during an earthquake, often requiring demolition and rebuilding. In contrast, mass timber is more ductile, so it can withstand more twisting and bending before failing.
Hype or reality?
In his TED Talk, Michael Green indicates that a billion people live in poverty, and another 100 million are homeless. Currently, half of humanity resides in cities; by 2040 this percentage will increase to three-quarters. And over these 20 years, an estimated 3 billion people will need a new home.
Instead of using concrete and steel to construct those new homes, Green suggests mass timber. In recognizing the stress this material might put on global forests, which are already experiencing innumerable pressures, he argues: “There are models for sustainable forestry that allow us to cut trees properly, and those are the only trees appropriate to use for these kinds of systems. Now I actually think that these ideas will change the economics of deforestation. In countries with deforestation issues, we need to find a way to provide better value for the forest.” Commendable, but is this doable?
The Food and Agriculture Organization of the United Nations (FAO) notes that forests cover 31 percent of the global land area. Since 1990, we’ve converted 420 million hectares of forest to other uses. Although the annual rate of deforestation has slowed since 2015, we’re still losing 10 million hectares annually (down from 16 million hectares). The biggest drivers of deforestation are agriculture, urbanization, and mining. And the impetus fueling those drivers is population growth.
Green’s optimism for sustainable forestry is noteworthy, but I wonder if it’s a feasible solution, especially when considering the Amazon rainforest, which usually dominates any discussion about deforestation. Straddling eight countries, it covers an area equivalent to the 48 contiguous states. During a typical year, agriculture, development, and illegal logging claim 5 million acres. That’s 13,700 acres daily, 570 acres hourly, 76 acres while reading this post.
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It’s believed we’ve lost 17 percent of the Amazon to deforestation, and the effects are telling—changing regional weather patterns are decreasing the volume of rainfall while increasing the frequency and intensity of droughts. Everything has a tipping point; scientists think the Amazon’s is 20 or 25 percent. Once that’s breached, the world’s largest rainforest could likely become a dry savannah that leaches more carbon dioxide back into the atmosphere than from it. Sadly, this isn’t conjecture; we’re already seeing the “lungs of the world” struggling to breathe. According to a recent study published in Nature, the eastern portion of the Amazon emits more carbon than the western portion because “over the past 40 years, eastern Amazonia has been subjected to more deforestation, warming and moisture stress than the western part.”
The stakes are high—not just for the Amazon but for the world, which is itself experiencing droughts, famines, deforestation, pollution, overpopulation, political turmoil, and so much more. It will take many different tools and technologies to mitigate the worst of climate change. Mass timber may very well be one of those tools. But only if we proceed with great caution. As a species, we have a terrible record of destroying nearly everything we touch. If we play our cards wrong, mass timber could easily push us further into the climate change abyss instead of away from it.
Further reading
“Create a Mass-Timber-Piece.” Think Wood, 2022.
Green, Michael. “Why We Should Build Wooden Skyscrapers.” TED Talk, 2013.
Hadley, Alexander. “Mass Timber in the Age of Mass Extinction.” Failed Architecture, March 11, 2021.
Kimbrough, Liz. “More Droughts Are Coming, and the Amazon Can’t Keep Up: Study.” Mongabay, September 16, 2022.
Paul, Bell. “Amended 19th Century Laminated Timber Roofs in England.” Academia, no date.
“History of APA, Plywood, and Engineered Wood.” APA – The Engineered Wood Association, 2022.
Rockett, Connor. “Mass Timber Goes Primetime.” New England Forestry Foundation, January 13, 2022.
Schulman, Pansy. “Mass Timber: A New Chapter in Sustainable Forestry?” Architectural Record, August 15, 2022.
“The State of the World’s Forests 2020.” Food and Agriculture Organization of the United Nations, 2020.
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