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The push to return to building skyscrapers and other tall buildings mainly out of wood recently received a big vote of confidence from a company well known for steel and concrete towers.
Skidmore, Owings & Merril, designers of a long list of skyscrapers—including the nearly complete One World Trade Center in New York City—has released a report showing how it could use mainly mass timber to build a 42-story residential tower.
According to the report, the “Concrete Jointed Timber Frame” system “relies primarily on mass timber for the main structural elements, with supplementary reinforced concrete at the highly stressed locations of the structure: the connecting joints.”
The final makeup of the system is 70 percent wooden columns and slabs with the remaining 30 percent, such as the foundation, being concrete. The report finds the system “technically feasible” but concedes that more research and a great deal of physical testing are required to be sure.
The main reason behind the push to return to wooden buildings is to reduce the carbon footprint of construction, especially since more and more buildings will be needed to house the growing population of Americans moving to the city. The Skidmore, Owings & Merril says this new system has a carbon footprint 60 to 70 percent lower than constructing a similar building of steel and concrete.
As an article from the New York Times notes, there would be a few obstacles to overcome. First, the 42-story tower outlined in the report would required 3.9 million board-feet of wood. For comparison, the typical single family home uses 20,000 board-feet of lumber. The impact such an increased use of timber would have on forests is unclear.
And then there’s the matter of building codes. Most building codes limit wooden structures to four stories, not to mention the concern many have with a wooden building’s ability to meet the fire safety standards of concrete and steel buildings. However, advocates of wooden buildings say mass timber does not ignite easily and when it does slows burning with a layer of char.