Thanks to advances in wood construction, the next generation of skyscraper might be made of spruce, not steel. Architects are designing wood buildings that ditch concrete and steel in favor of a more environmentally friendly material — one that could help fight climate change.
Glue might the best thing to happen to the lumber industry. Adhesives permit manufacturers to cheaply produce wood products that are no longer in the shape of trees. The particleboard in your IKEA coffee table, for example, is made from wood fragments that have been glued together.
Lumber producers are now using über-powerful adhesives to assemble massive wood panels with the strength and durability of concrete and steel. Cross-laminated timber, as it’s known, is made of small planks bound together by a polyurethane adhesive. The pioneering technology has freed architects to dream up buildings that were previously inconceivable.
“Not only is [wood] attractive and warms up the building,” said Kris Spickler, a heavy timber specialist at cross-laminated timber manufacturer Structurlam, “I think architects really enjoy being able to use a product that they’ve used for interior spaces, and actually use it for the structure itself.”
Beyond its aesthetic appeal, cross-laminated timber boasts several other advantages. Wood construction sites generate less waste, noise, and traffic than conventional sites. And wood buildings can be erected more quickly than steel and concrete structures, keeping the projects cost-competitive. Spickler pointed to a forthcoming skyscraper at the University of British Columbia.
“The building was competitively bid against concrete and steel. It wasn’t a show project,” said Spickler. “I think the speed and the affordability won out, and that’s why we’re building that 18-story.”
To observers, a wood skyscraper may sound like a fire hazard, but Spickler disagrees. Steel is vulnerable to melting in a blaze, twisting and contorting in the heat. Timber, on the other hand, will char on the outside, but flames will not penetrate its core. After the fire recedes, the wood beam will remain standing.
Wood’s greatest virtue, however, is not design potential or fire safety. The fibers of every plank help combat climate change.
Steel and concrete produce carbon dioxide
Steel and concrete come with a colossal carbon footprint. Cement, the binding agent in concrete, is made by heating limestone and clay in a kiln. Steel is made by heating limestone, iron and a carbon-rich form of coal called coke in a blast furnace. Carbon dioxide is an inevitable byproduct of both processes from burning coal to generate heat.
According to a 2013 analysis from Ecofys, iron and steel account for nearly 5 percent of global greenhouse gas emissions. Non-metallic minerals, including the raw ingredients in concrete, amount to 6 percent. Together, these sources contribute about as much to climate change as all the cars and trucks on Earth.
Wood traps carbon dioxide
When it comes to climate, wood beats conventional building materials on two fronts. First, wood boasts a smaller carbon footprint than steel and concrete. Logging, refining and shipping wood products eat up fossil fuels, but a producer will generate more pollution turning a lump of iron into a steel beam than he will turning a tree into a plank of wood.
Wood’s second advantage is its ability to trap carbon dioxide. Some scientists speculate the only way to keep warming under two degrees Celsius, the stated goal of the Paris Climate Agreement, is to removed carbon dioxide from the atmosphere. That could mean high-tech machines or materials that scrub CO2 from the air, or eco-friendly farming practices that trap carbon in the soil. So far, however, the most cost-effective tool for carbon removal is a tree.
“If we built a 20-story building out of cement and concrete, the process would result in… 1,200 tons of carbon dioxide,” said architect Michael Green in a TED Talk. “If we did it in wood, in this solution, we’d sequester about 3,100 tons, for a net difference of 4,300 tons. That’s the equivalent of about 900 cars removed from the road in one year.”
Green’s back-of-the-envelope calculation lines up with more rigorous analyses. According to a 2014 study from researchers at Yale and the University of Washington, as much as 31 percent of global carbon dioxide emissions could be avoided by building with wood instead of steel and concrete.
“If you build out of wood instead of concrete or steel or brick, then you avoid all that fossil fuel you would burn to make the steel, concrete and brick,” said Chad Oliver, Director of Yale’s Global Institute of Sustainable Forestry and lead author on the study. He noted that, because timber weighs less than conventional materials, builders also need less concrete to lay the foundation of a wood structure. And, when a wood building is finally retired, its component parts can be reused in other buildings, buried in the ground or used to produce electricity.
The prospect of leveling forests to erect skyscrapers and generate electricity is enough to make any tree hugger woozy. But Oliver says logging can form an essential part of smart forest management.
“As a general rule, and this varies from place to place, the forests are getting more dense,” said Oliver. “You want some areas that are dense, but you don’t want to whole forest uniformly dense, because some animals live in that dense forest, but other animals live in an open forest. You need a diversity of conditions.” Loggers can foster biodiversity by thinning some parts of the forest and clearing others to create patchwork quilt of habitats where every species has a home.
Logging can also reduce the risk of forest fire. In a uniformly dense forest, flames grow hot and spread quickly through tightly packed trees. In a more varied setting, a fire might hit a meadow and slow down, allowing time for rain or cold to intervene and bring the inferno to a halt.
“If we harvested more of that extra [tree] growth instead of letting it rot or burn in overly dense forests,” said Oliver. “We could make a lot more products and use the waste for wood energy.”
Cross-lamination allows manufactures to produce larger beams from smaller pieces of wood, meaning the raw materials can be supplied by shorter, more slender trees, including those threatened by rot, fire, and pine beetles. Trees that would otherwise decay or burn, leaking their stores of carbon into the atmosphere, can be made into the building blocks of skyscrapers.
“We have more trees right now in the forest that we can use than we did 50 years ago. So, we can sustainably grow this and harvest it and continue to use it,” said Spickler. “We can take these smaller trees and take the smaller cuts of them, and laminate panels that weigh 10,000 pounds — massive panels bonded together to be stronger than concrete and one fifth the weight.”
Climate change has already ignited revolutions in clean power and transportation. Spickler believes construction may be next. “This revolution has happened rather quietly and happened rather slow,” he said. “But I think we’re in a year right now where we’re going to see it explode.”