Since the first skyscraper was built in 1884 in Chicago, tall buildings have traditionally used steel and concrete materials—until now. Several building and architectural groups are making a case for tall wooden structures, buildings built primarily out of wooden materials. In the last several years, many of these structures have sprung up all over the world. One of the most outspoken proponents for wood structures is architect Michael Green who wrote a 240 page case study called: The Case for Tall Wood Buildings. For a briefer version, watch his TED Talk HERE. In this case study, Green talks about the various benefits of moving to wooden structures while addressing many of the concerns them.
Building a greener, less expensive world
Some of the primary reasons for moving to wooden structures include: attacking climate change, creating more sustainable development, reducing construction waste and addressing socio-economic issues throughout the world.
Steel production represents around 3 percent of human greenhouse gas emissions, concrete accounts for around 5 percent and the building industry in general (materials, machinery, vehicles, etc..) makes up almost half of greenhouse gas emissions in the United States. This is compared to 33 percent linked to public transportation in the United States. Using sustainable forestry practices, wooden structures dramatically reduce the amount of carbon released during all phases of construction.
Beyond climate change, the environmental reasons for wood construction are many—wood is a more sustainable resource (if responsibly harvested), it produces less job site waste, wood is compostable and it takes less energy to create wooden beams.
The upfront price difference for wood vs traditional materials isn’t substantial, usually ranging from similar costs to slightly less (averaging 2 percent to 4 percent), depending on construction methods. Where there is a significant difference is the time it takes to construct mass timber structures. In a recent study, an apartment building in Melbourne, Australia was built 30 percent faster because of CLT (cross laminated timber) and prefabricated panels. Additionally, wood materials tend to weigh less, which can reduce the foundation requirements resulting in less materials used.
Wood equals fire, right?
When you hear about tall wooden structures, your mind likely goes to the danger of fire, and rightly so. After all, isn’t wood extremely flammable?
Engineers have designed ways to address the issues of fire, the most common is simply knowing the rate in which heavy timber burns. The methods are many, and Michael Green’s above mentioned case study addresses many of them, with the “charring approach” being discussed in detail. In a nutshell, the charring approach allows for a layer of protective wood around supportive beams that creates a slow charring rate that protects the structural timber so the building remains standing, even at high temperatures. Knowing how long it takes for different widths of wood to char at high temperatures allows the designer to create safer building structures. Think about campfire logs. How long does it take for thick logs to completely burn compared to thin tinder? With that in mind, add additional safety systems in place—like sprinkler systems, firefighter elevators and advanced alarm systems—and the fire argument starts to loose traction.
A different frame of mind
When we think of wood structures our mind will likely go to the familiar wooden frames of houses and shorter structures. Mentioned above, cross laminated timber is becoming a new standard of building taller structures. This method laminates wood in alternating grain directions to create thicker beams that are much stronger than conventional wood-frame structures built with two-by-fours.
While tall wooden structures may not yet be the norm in most cities, they are certainly a growing trend to watch. Some day in the future, most new buildings may utilize these methods and materials to create beautiful wood structures.
If you have further questions about the validity of wood construction, this article address them statistics, facts and charts: http://www.treehugger.com/green-architecture/guardian-covers-tall-wood-construction-we-cover-comment-section.html