By the fall of 2016, the International Code Council (ICC) will begin announcing some of the findings of its newly created Tall Wood ad hoc committee. This group—a cross-disciplinary team consisting of architects, engineers, code officials and manufacturers—has begun exploring the building science associated with “tall wood” structures that use Cross-Laminated Timber (CLT), Laminated Veneer Lumber (LVL) and Laminated Strand Lumber (LSL) in framing buildings taller than six stories.
One of the biggest obstacles to Tall Wood construction in the United States is that many cities have fire codes that don’t permit wood-framed structures higher than four to six stories. Ironically, some of the same cities that once had eight-story heavy wood structures in the early 1900s now strictly forbid them. But firefighting practices have gotten much more sophisticated since that era. So have the materials used in fire-resistant walls and floors. Many architects and builders are now augmenting traditional gypsum with engineered materials that deliver the same fire resistance properties while lowering installation costs and reducing construction time.
Currently, IBC Section 104.11 covers alternative materials and construction methods—and it permits wood-framed structures higher than six stories after meeting code and consulting with code officials. But exceeding the six-story mark is still rare in the United States. One of the recipients of the U.S. Department of Agriculture’s Tall Wood building competition is planning a 12-story mixed-use structure in Portland, Oregon.
There are already Tall Wood buildings in other nations that exceed that height—and some are being planned that will reach 30 stories. One of the chief objectives of ICC’s new Tall Wood committee is to determine whether U.S. code can eventually align more closely with international standards. The first IBC code changes (if any are recommended) would be part of the 2021 edition.
Tall Wood structures have a bright future, according to architectural firm Skidmore, Owings & Merrill (which built both the Freedom Tower in New York City and the Burj Khalifa in Dubai, the world’s tallest building). In a 2014 study, the firm found that a 38-story wood structure was technically feasible—and that it could compete on price with conventional construction while cutting the carbon footprint up to 75 percent.
In designing a nine-story Tall Wood building in London, England, Waugh Thistleton Architects chose engineered wood over conventional wood for its enhanced strength. Engineered wood materials made of CLT, LVL and LSL also complement each other—providing greater overall strength and design values than what a single material could provide. As wood structures grow taller, they can also benefit from fire-resistant materials that help meet code while reducing dead load and wall thickness.
Most researchers agree that Tall Wood skyscrapers will never match the height of conventional ones. For example, Freedom Tower is 104 stories and the Burj Khalifa is 163 stories. But if Tall Wood structures can capture just 15 percent of the North American market, there would be 2.4 billion board feet of wood used annually in those projects. That’s why builders are paying close attention to what the ICC Tall Wood committee ultimately recommends.
To learn more about how fire-resistant materials and engineered wood are providing momentum for Tall Wood construction, visit LPCorp.com/FlameBlock.