What carbon fiber is to titanium alloy in aerospace, engineered wood is to concrete and steel in commercial construction. Engineered wood beams, columns and panels are strong, lightweight, aesthetically pleasing and low-maintenance. An increasing number of developers, design teams and contractors see engineered wood, "mass timber" construction as a way to innovate and lead.
Sustainability and Aesthetics
Plywood first gained acceptance because it could turn relatively small-diameter trees into strong, economically-priced, laminated construction products. Similarly, the cross-lamination (CLT) process turns small-diameter trees into economically-priced lightweight beams and panels. Costs are competitive with concrete and steel, but the beams and panels are far lighter. Glue, nails or dowels hold the cross-laminated layers together. The wood's natural beauty eliminates the need for drywall or paint.
Engineered wood is highly sustainable because it is possible to use wood from younger trees which are readily re-planted and re-harvested. Yellow pine, Douglas fir and Western hemlock are some of the softwoods that serve as the raw material for CLT products.
Mass timber potential for mid-rise commercial construction is significant. Cees de Jager of the Softwood Lumber Board estimates that 9 of 10 nonresidential structures less than 12 stories high are of concrete and steel construction. He calculates that most of these buildings could be constructed using mass timber construction instead. Mass timber designs taller than 12 stories are also in the works. A 14-story building in Portland is slated for completion in 2018.
The engineered wood movement is rapidly becoming more mainstream. This year's International Mass Timber Conference was March 20-22 in Portland, Oregon. More 800 industry professionals from 22 countries attended the event. Some have heralded the proliferation of mass timber tall buildings as the beginning of a new era in commercial wood construction.
Mass Timber Construction Advantages
Mass timber tall buildings are gaining wider acceptance for a variety of reasons related to sustainability, structural advantages and economical construction techniques.
Precise fit and finish - Although wood may seem like an old-fashioned construction material, mass timber components fit together so well that a tight, energy-efficient envelope results.
Quicker on-site construction - Prefabricated sections are typically created in a controlled factory setting before being efficiently assembled at the project site. Mass timber construction methods promote accuracy and safety.
Address labor shortages - On-site assembly of mass timber structures requires relatively fewer skilled tradespeople than traditional concrete and steel construction. Regions with seasonal skilled labor shortages benefit from engineered wood projects.
Compact footprint - When a land parcel so requires, mass timber construction makes relatively large interiors possible, even when the overall footprint of the building is limited.
Insulating properties - Steel beams conduct heat and cold, while wood beams are not nearly as conductive. Wood's thermal qualities are particularly beneficial in multi-story structures.
Seismic resilience - Laminated timbers offer resilience in seismic occurrences. Its relatively lighter weight reduces foundation loads, another advantage during seismic events.
Fire resistance - Although it may seem counterintuitive, mass timber construction offers substantial fire resistance. Large, laminated timbers and panels resist fire intrusion deep into the wood, providing essential first responder safety.
Going forward, more consistent demand will interest more manufacturers in making the multi-million dollar investment in CLT assembly lines. U.S. code changes will also promote mass timber construction. Since Canadian codes tend to already be more performance-based than material-based, the climate there is somewhat more amenable to engineered wood projects.
Case Studies
Although a fair number of mass timber tall buildings around the world are residential in nature, there are already a number of commercial and multi-use structures in place.
T3 - Minneapolis
The acronym T3 stands for timber, transit and technology. This 7-story, 220,000 sqft commercial building in Minneapolis was designed by Vancouver-based Michael Green Architecture. Laminated timbers and pre-fabricated 8-ft by 20-ft wood panels combined to make it the largest engineered wood building in the United States when it was completed in 2016. The design offers a high degree of sustainability, and it required no code exemptions. Amazon is a tenant.
Riverfront Square - Newark
Now, the same design firm has been commissioned to design another such project more than twice as large as T3. It will be located in Newark's Riverfront Square, an 11.8-acre mixed-use development along the Passaic River. The mass timber project includes more than 500,000 sq-ft in three conjoined structures, six, eight and 11 stories high. Michael Green says, "Good buildings are good neighbours and we envision a sustainable, efficient and architecturally stunning future for Newark."
Arbora Complex - Montreal
Another one of the North American continent's largest mass timber projects is Montreal's Arbora Complex, a three-building cluster encompassing 600,000 sq-ft. The eight-story engineered wood structures will include at least 40-percent green space, in accordance a goal to achieve LEED Platinum certification. The wood beams, columns and panels contribute to economical manufacturing, shipping and assembly processes. The complex will house more than 300 condominiums and townhouses along with 130 rental units.
Carbon12 - Portland
According to The Architect's Newspaper, construction of Carbon12, an eight-story mixed use building, was completed in 2017. It features a hybrid design, with mass timber construction surrounding a steel core. Although striated metal panels cover the exterior, the interior surfaces of the CLT slabs, columns and beams remain exposed for a warm and inviting feeling. The significantly sustainable design also features a rooftop solar installation.
In 2018, Portland will also be home to an even taller mass timber structure. The 12-story Framework building will be 148-ft tall. Floors will be comprised of CLT slabs up to 40-ft long. The design promotes the use of low-carbon, sustainable construction. The project "targets energy savings of 60% when compared to code." The need for lateral seismic stability is addressed with a "post-tensioned rocking wall cross-laminated timber (CLT) core."
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