LAS VEGAS, NV, June 8, 2019 – One of my favorite types of events to post on this website are panel discussions about cross-laminated timber (CLT,) because they’re panel discussions that are literally discussions about panels. It makes sense to me. I get it. And when it comes to these literal panel discussions, nobody does it better than Portlanders.
Portland is honored to be the home of multiple architecture firms pioneering the technology of CLT and mass timber. We’re the home of multiple CLT manufacturers. We’re the home of the International Mass Timber Conference year after year. We’re the home of Carbon12, the tallest CLT-framed building in the United States, designed by local firm PATH Architecture. Another local firm, LEVER Architecture*, was one of only two firms in the country to be awarded a $1.5 million award from the US Tall Wood Building Prize Competition, used to offset the costs of testing and peer review of their (currently on hold) project Framework, to ensure compliance above and beyond current building codes. Finally, just down I-5, Oregon State University is home to the TallWood Design Institute, in collaboration with the University of Oregon.
It comes as no surprise, then, that when one of these literal panel discussions took place at the 2019 AIA Conference on Architecture (A’19,) featuring a couple of Portland’s pioneers in the field, tickets to this event sold out fast. As Portland Design Pup continues our coverage of A’19, we focus on this panel, which consisted of four innovators in the field sharing their expertise of four different aspects of CLT high-rise construction: Environmental Benefits, Research/Development, Acoustics, and Construction/Cost. Here’s what they had to say.
Richard opened his portion of the discussion by sharing the fact that in 1920 there were 745 million acres of forest in the United States. While wood continues to be harvested, this number has remarkably remained unchanged, remaining at 745 million acres today, due to the ability of forests to regenerate. Manning acknowledged that the harvesting of forests does, of course, come with environmental costs including landscape degradation, erosion, loss of habitat, and degraded water quality, but noted that timber is a renewable resource, meeting the definition of sustainability as defined by The Brundtland Report, or Our Common Future:
[Sustainability is defined as] development that meets the needs of the present without compromising the ability of future generations to meet their own needs.
–Our Common Future, 1987
“Timber is pretty low in embodied carbon, compared to concrete and steel,” Manning explained, noting that it takes about 2x-3x the amount of timber to equal the amount of embodied carbon in concrete or steel.
Forestry practices continue to evolve and improve, as well, with the advent of forest management initiatives, including the Forest Stewardship Council (FSC,) founded in 1993, Sustainable Forestry Initiative (SFI,) 1995, American Tree Farm Association, 1941, and a variety of other state regulations including California, which meets or exceeds FSC and SFI in multiple key areas.
Manning concluded his environmental portion of the presentation by highlighting some of CLT’s most notable environmental benefits, including their use of wood that has sequestered carbon, is recyclable and biodegradable, and creates jobs in rural communities. He noted that since CLT is constructed of smaller diameter wood, younger or fallen trees can be utilized, rather than relying on old-growth trees.
Research + Development
Since CLT is a relatively new material, there is much research to be done in areas including cost, design, manufacturing, construction, building codes, engineering and more. At the forefront of this research is the TallWood Design Institute (TDI,) an “industry-driven partnership” between the Oregon State University College of Forestry, University of Oregon College of Design, and Oregon State University College of Engineering. TDI’s goals are to increase manufacturing of mass timber products in the United States, increase demand for these products, and eliminate barriers for their use in the construction industry.
Macdonald’s presentation featured a series of cool images and videos showing the seismic testing research and fire research that the team is doing on full-scale mass timber mockups. Research in the seismic and structural realm includes post tensioning of the structures, shear wall assemblies, splice testing, and connection testing. These tests are conducted digitally, physically via models, and are being tested in the field via lessons learned in the construction of new CLT buildings around our region and around the country.
Of course fire safety is being carefully tested, as well, with Macdonald explaining the “charring layer” of mass timber products, or the addition of 1 inch in thickness of a material for every hour the material burns. He closed his discussion of CLT testing by discussing the role of moisture in the products, noting that while water can and does cause visual staining, their research has not indicated that any structural issues result from water intrusion.
So what’s next for CLT? With over 500 CLT projects currently going on around the country, more contractors will be educated on their construction, codes will begin to adapt, connections and assemblies will become more standard, and costs will continue to decrease as the material becomes more mainstream. As the product evolves, Macdonald envisions advancements including hybrid panels, panels pre-constructed with insulation or exterior cladding, smart sensors, or other technology. He also mentioned the potential for 3D printed connections, and the possibility of robotic fabrication or assembly.
“Wood is not good for acoustics. That’s the simple, honest truth,” Meszaros opened with, much to the chagrin of every architect in the room. While covering up all the CLT in a building with gypsum board may be the easiest way to achieve desired acoustic performance in a CLT building, it’s often not the ideal way. Enter people like Meszaros, who gave the Las Vegas Convention Center ballroom audience a crash course in acoustic education. Recognizing that acoustics is a concern in mass timber construction, Steve’s primary recommendation is that “early planning and good design is paramount to success.”
Steve discussed the fundamentals of acoustics, including frequency and pitch, Sound Transmission Class (STC) ratings, flanking paths, and Impact Insulation Class (IIC) ratings. Way more than we can (or should) cover in this article, but that you can learn more about in books like Mechanical and Electrical Equipment for Buildings (MEEB,) co-authored by Alison Kwok, FAIA, featured elsewhere in our series of A’19 articles. Steve continued his discussion of acoustic fundamentals by explaining how poorly CLT rated in virtually every aspect of sound performance.
While CLT in itself may perform acoustically poorly, materials, assemblies, connection details, sound isolation products, and a host of other factors can be used to mitigate this negative aspect of the product. Meszaros reiterated the importance of considering acoustics early in the project, when the ease of change is high and the cost of change is low. Just, for the love of God, don’t leave all of your CLT exposed, was the big takeaway from this portion of the presentation.
Construction + Cost
Scott Noble wrapped up the presentation by discussing the construction and cost of high-rise CLT structures through the lens of four case studies. He began by noting that every CLT building is a hybrid building in some capacity, as “Every high rise starts with a hole in the ground, filled with concrete and steel.” As the building rises, this hybrid approach continues as other materials are used for the lateral structural system. In the case of Carbon12, a project Noble himself led, steel was used to achieve this. In Brock Commons, a mass timber high-rise in Vancouver, BC designed by Acton Ostry Architects, a pair of concrete cores were used.
Noble went on to discuss the variety of ways in which CLT components can be connected, both with each other and with steel or concrete components. He illustrated this with the Ricon and SDS connections of Carbon12, Bucket connectors of The Radiator, and Two-way CLT connections of Brock Commons.
Noble wrapped up with what was frankly a very well-done overview of the cost of CLT, where he compared Building Value with Building Cost. In the case of Carbon12, total cost for the hybrid mass timber/steel structure alone equaled around $42/sq. ft. While the cost of an equivalent structure constructed of concrete would have been cheaper – $39/sq. ft. – this process would have added 10 weeks to the construction timeline, meaning that while concrete seemed to be a lower initial cost, the value of the project actually increased with the steel/mass timber combination.
Noble continued with another example , illustrated by The Canyons, a PATH Architecture-designed project currently under construction in Northeast Portland. Facing challenges in the project budget, the team looked at replacing a portion of the CLT-framed structure with I-Joist light wood framing. While the material change itself would have saved the project nearly $100,000, due to the increased timeline of construction and added scope to the project that the change would have triggered, this move would have actually resulted in an added cost of over $140,000!
The team repeated this exercise, this time deleting all CLT, which all-told saved the project over $240,000. However, the team then reviewed the loss of value of things like a reduction in ceiling height, loss of exposed ceilings, loss of market differentiation, and were able to attach numbers to each of these items of value. The result? A loss of over $1.7 million (!!) by the time of building sale. Moral of the story? Numbers are one thing, but there’s more to the value of a building than numbers alone.
And with that, the panel discussion featuring a discussion about panels came to a close. By the way, who else is tired? This presentation was heavy on numbers, facts, and figures, but man, what a valuable presentation it was. How fortunate we are as a community to be at the epicenter of the mass timber movement, and to have these members of our community who are so knowledgeable, passionate, and willing to share their work in CLT and mass timber. I can’t wait to see their work evolve over time, and continue to capture the imagination of architects around the country.
Anyway, I’m going to make like a tree and take a nap…for rest…
Portland Design Pup traveled to Las Vegas, Nevada for the AIA Conference on Architecture 2019 this past June 6th-9th to explore the influence that Portland architects and designers are having on the national architecture scene. We attended four sessions led by Portlanders, as well as the investiture ceremony for the 2019 Class of Fellows, which included five Oregon architects. We will be sharing images and recaps of each event in a 5 part series of articles, of which this is the fourth.
About the AIA Conference on Architecture 2019
Every year the AIA Conference on Architecture travels to an iconic city for three immersive days of what’s new and now in architecture and design. Industry leaders and experienced professionals attend A’19 in search of the hottest new products and technologies.
*LEVER Architecture is a sponsor of Portland Design Pup.
Images courtesy Timothy Niou Photography unless noted otherwise. Note: Our coverage of the Conference is not affiliated with or endorsed by AIA, AIA Portland, or AIA Oregon.