Worldwide, the construction industry is buzzing about wood.
Walmart plans to build its new 2 million-square-foot Arkansas headquarters campus of wood. An 18-story mixed-use structure in Norway currently holds the title of world's tallest wooden skyscraper. A renowned international architecture and design company has proposed an 80-story residential tower for Chicago.
An 80-story wooden building in, of all places, Chicago? Site of the 1871 Great Chicago Fire, which roared through more than 3 square miles of mostly wooden buildings and killed 300 people? Are they kidding?
Proponents say using wood instead of concrete and steel for buildings could significantly reduce the carbon footprint of the construction industry, improve earthquake resilience, and reduce waste, pollution, and costs.
Skeptics counter: Yeah, maybe, if it's done right. They question how sustainably the wood will be harvested.
We're not talking about 2-by-4 framing and 4-by-8 sheets of plywood. Instead, architects and builders are using mass timber (short for "massive timber"). That's small pieces of soft wood stuck together to create large—sometimes VERY large—slabs, columns, and beams.
The most common form is cross-laminated timber, or CLT. Manufacturers stack layers of kiln-dried boards in alternating directions and glue them together with industrial adhesives. That creates a solid rectangular slab, up to a foot thick, that can match or exceed the performance of concrete and steel despite being much lighter.
Mass timber performs very well in earthquakes. It even resists fire. Large, compressed masses of wood don't ignite easily, as anyone who's built a log fire can attest.
CLT can be used for floors, walls, and ceilings. The pieces are precision-cut at the factory to the building's exact specifications, with openings for walls and doors, and space for plumbing and electrical lines.
It takes relatively few construction workers to put them into place. On the other hand, greater use of mass timber would increase the demand for lumberjacks and sawmill workers.
But will it really help in the fight against climate change?
That mostly depends on how sustainably the wood is harvested. If swaths of forest are clear-cut to produce the timber, then no.
On the other hand, if harvesters selectively thin out small and weak trees, then that could actually improve the health of forests and make them more fire-resilient, while also reducing the amount of carbon emitted into the atmosphere because of construction.
For a comprehensive outline of the pros and cons, see this story by David Roberts of Vox. And for an in-depth look at the sustainability of mass timber, read this story from the Yale School of Forestry & Environmental Studies.