Building Wood Towers
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construction materials AIA CONTINUING EDUCATION building wood towers HOW HIGH IS UP FOR TIMBER STRUCTURES? COURTESY AART ARCHITECTS The Waterfront, a 128-unit wood-based residential development in Stavanger, Norway, designed by AART architects and Kraftvaerk for client Kruse- Smith. This first phase was completed last July; a second phase is under construction. More than 80 firms competed for the project. BY C.C. SULLIVAN, CONTRIBUTING EDITOR LEARNING OBJECTIVES After reading this article, you should be able to: he recent push for larger and taller wood structures may seem + DESCRIBE the primary approaches to large-scale like an architectural fad—plenty of hype, but only a few dozen structural wood construction, including hybrid light Tcompleted projects globally. Concrete and steel still rule the framing and engineered mass timber. world of mid- and high-rise construction. + DISCUSS the benefits and drawbacks of structural wood Still, Building Teams around the world are starting to use more systems, in particular their contribution to sustainable large-scale structural wood systems, including heavy timbers, design and green building. engineered framing systems, and other modern wood products. The + LIST current certifications, codes, and standards that number of new buildings of this kind has been trending modestly up- affect the use of large-scale modern wood structures. ward, spurred by such benefits as sustainability, cost effectiveness, + COMPARE wood systems to concrete and steel in and reduced construction impact. Leading the way: podium-type terms of availability, suitability for building types, and concrete and light-framed hybrids in the U.S., and heavier “mass performance for such factors as acoustics and fire safety. timber” structures elsewhere. 64 APRIL 2015 BUILDING DESIGN+CONSTRUCTION www.BDCnetwork.com International real estate firm Lend Lease (www. lendlease.com) used cross-laminated timber (CLT), sometimes described as “precast timber panels,” for its 10-story Forté apartment tower in Melbourne, Australia (which has been called the world’s tallest structure of its type) and in the $18 million Library on The Dock, the first public building in Australia made with CLT. In the United States, Hines Interests (www.hines.com) recently announced plans for a seven-story wood-framed office building in Minneapolis. Other examples include the nine-story Stadthaus tower in London by developer Telford Homes (www. telfordhomes.plc.uk) and affordable housing man- ager Metropolitan Housing Trust (www.metropoli- tan.org.uk), with its cellular structure of a load-bear- ing core and timber floor slabs. From commercial projects like The Waterfront, a 210,000-sf mixed- use project in Norway, to the University of British Columbia’s five-story Earth Sciences Building academic wing, platform framing and distributed post-and-frame structures are attracting interest. The Treet building in Bergen, Norway, reached 14 COURTESY AART ARCHITECTS stories with all-timber bones. There’s the eight-story Stavanger, Norway, site of The Waterfront, claims to have the highest concentration of LifeCycle Tower One, in Dornbirn, Austria, which wooden architecture in Northern Europe. The lower flats are single-story; the upper flats are duplexes. All 128 units are daylit from both sides to provide views of the sea and the city. The used wood as its primary building material. Struc- 19,500-sm complex won a 2014 WAN Resident Award and was a finalist for a MIPIM award. tures up to 30 stories in height are on the boards in Norway, Austria, and Vancouver, B.C. special quality of space, contributing to a feeling of warmth and well- Last year, the Vancouver, B.C.-based Forestry Innovation Invest- being and supporting exceptional building performance.” ment and Binational Softwood Lumber Council commissioned There is a strong case for wood’s reduced environmental Perkins+Will (www.perkinswill.com) to interview building owners, impact, mainly that less carbon is released during its manufacture designers, contractors, timber fabricators, and authorities having compared to other structural materials. There’s the added bonus of jurisdiction for a global study of the prospects for big timber. The carbon sequestration (absorption) during the life of every tree. “The resulting “Survey of International Tall Wood Buildings” catalogues 10 main motivation for Building Teams going bigger and taller is the novel projects in detail. environmental aspect,” says Scott Breneman, PhD, PE, SE, a Senior Technical Director in Architectural and Engineering Solutions for ASSESSING THE BENEFITS OF WOOD WoodWorks (www.woodworks.org), an initiative of the Wood Prod- Teams from around the United States have submitted projects for ucts Council, which represents North American wood associations. the $2 million purse in the U.S. Department of Agriculture’s U.S. Tall “There are many different ways to measure it, but there is much less Wood Prize Competition competition. Winners will “showcase the carbon released during manufacture than with other, more energy- architectural and commercial viability of advanced wood products intensive manufacturing processes such as those for steel, concrete, like CLT in tall buildings,” said Doug McKalip, a White House Senior or masonry.” Much of that process energy comes from renewable Policy Advisor for Rural Affairs. He estimates that “the near-term use biomass, such as bark and other residual fiber, instead of fossil fuels. of CLT and other emerging wood technologies in buildings of seven Breneman also points to life cycle studies showing lower across- to 15 stories could have the same emissions-control effect as taking the-board environmental impacts for wood from cradle to cradle more than two million cars off the road for one year.” compared to other materials. Sustainability is not the only reason for greater interest in wood Sustainability was a major factor in prompting Skidmore, Owings structures. There is also the aesthetic appeal of wood—its earthy & Merrill (www.som.com) to publish its “Timber Tower Research colors and aromas, fine grains, durability, dimensional stability, and Project” in 2013. The report demonstrates the feasibility of a 42-sto- what carpenters call workability. ry mass timber high-rise with supplementary reinforced concrete at Wood is also considered a healthy material choice, says Rebecca the connecting joints. Holt, a Sustainable Building Advisor with Perkins+Will. “It creates a A top goal for SOM’s use of mass timber as the main structural www.BDCuniversity.com BUILDING DESIGN+CONSTRUCTION APRIL 2015 65 construction materials AIA CONTINUING EDUCATION material in the study was to minimize the embodied carbon footprint podium was limited to automobile parking, but few jurisdictions of the building by as much as 60–75%. The report urged additional now restrict the first-floor uses. Typical podium structures are called research and physical testing to verify structural and fire-safety per- five-over-one—five wood-framed floors on a concrete platform—but formance, and encouraged the design community to work creatively recently there have been more five-over-two projects, such as in with municipalities and code officials “to make timber buildings a Seattle, where the building code allows for a two-story podium and viable alternative for more sustainable tall buildings.” a combined building height up to 85 feet. The 160,000-sf Marselle Codes are already moving in the direction of allowing for multifamily complex in Seattle, designed by PB Architects (pbarch. larger wood structures, but not necessarily for mass-timber com) and structural engineer Yu & Trochalakis (www.ytengineers. skyscrapers. Buildings with light wood framing of up to six stories, com), used a two-story base to support five stories of light framing with up to four occupancy groups at each level, are allowable topped with a mezzanine level—in other words, 5.5 over two. under the height and area prescriptive language of the 2012 Inter- There are cost and schedule advantages for using wood in podi- national Building Code (http://publicecodes.cyberregs.com/icod/ um construction. If the Marselle condominium project had been built ibc/). Low-rise institutional and healthcare buildings can be made using all concrete, “it would have cost about 30% more,” says Kory of heavy timber (Type IV whole-building construction with solid or Knudson, Vice President of Norcon NW, the general contractor. “If glue-laminated members, wood decking, and structural sheathing we had built the entire project out of steel, it would have taken much with no concealed spaces), or they can have heavy timber roofs longer and we would have had to make many energy modifications.” in Type I and Type II buildings. These facilities can also meet code “These are lighter-weight materials, and the raw materials can with Type VA or Type IIIA construction, including one-story sprin- be economically designed, since the hybrid structure uses the klered facilities and certain others up to five stories. WoodWorks materials that are most readily available in the local markets,” says notes that beefing up the firewall and increasing the frontage can WoodWorks’s Breneman. He notes that, in the construction phase, further enlarge the allowable footprint. building with wood tends to be quieter and faster than that for other The IBC and local codes have also improved the prospects for materials, with fewer dirty, noisy processes like welding or grinding. schools, senior housing, office complexes, civic centers, and recre- “So there is a benefit to the community surrounding the construction ational buildings to use wood as a structural material for projects of site,” he says. up to five or six stories CLT and other panelized material methods and techniques can Increasing use of podium construction has led to imaginative and also speed on-site construction, thus helping to bring down labor safe mid-rise structures that combine a rigid lower portion (the po- allowances. “The concrete-and-steel hotel right behind Marselle dium), typically a concrete slab platform, with a flexible wood-frame had a similarly sized footprint, but our framing went up much upper portion.