Who doesn’t like wood? It’s gorgeous, warm, romantic and forever. The older the better. Smile, our future will be full of skyscrapers made with wood.
It’s a little surprising to hear this prediction considering the strict high-rise construction codes that disallow wood because fire can spread quickly from one wooden structure to another. It was the Great San Francisco Earthquake and the fires it caused that was the catalyst to move American construction away from tall wood buildings. Most state building codes now don’t allow construction over a certain number of feet – often around four stories.
New high-rises won’t be made of regular two-by-fours, however. Rather they’ll use a high-tech wood product known as mass timber. The framework of the skeleton will be made of glue-laminated timber or pieces of lumber bonded together into massive beams and columns. The walls and floors will be built with cross-laminated timber (CLT) panels in which layers of wood are stacked in alternating directions.
Albina Yard is a four story building in Portland, Oregon made of wood, not concrete or steel, to bear its weight. The architect behind the building is Thomas Robinson, of Lever Architecture, and pioneer in designing tall buildings with wood. His next project is a 12 -story mixed-use tower that will rise in Portland’s Pearl District scheduled for completion in 2019. When completed, it will be America’s tallest human-occupied all-wood structure.
Sounds great, because wood smells good and looks gorgeous and is certainly more inviting than steel and concrete. But, um, what about the fire thing?
Robinson’s team put both components through rigorous fire testing. A joined beam, column, and CLT panel were placed in a furnace, then weighed down with 25,000 pounds, to see how strong they would be after exposure to fire and heat. Two hours later, they emerged charred, but structurally intact. Mass timber doesn’t ignite easily—it’s more like a log than kindling. And the outer char layer that mass timber develops when burned actually insulates the wood.
But how could cutting down more trees be good for the service? Apparently, it is. The U.S. Forest Service is now handling out grants to architects using mass-timber and cross-laminated timber because we need to “thin” our overstocked forests to reduce fire damage.
According to Democratic Senator Jeff Merkley from Oregon, where timber is a huge industry, “what we know is that when a fire runs into a thinned forest . . the fire just stops. It proceeds to not have the fuel on the floor, and not have the ability to leap as easily from tree to tree. And there was a fire aimed right at Sisters, Oregon and it came to an area that had been thinned, and the fuels had been reduced on the floor of the forest, and it slowed down, and basically stopped.”
I think we’re going to enjoy the beauty of wood built skyscrapers.