Next generation of high-rise buildings might use advanced engineered wood for structural integrity and sustainability, but what are the risks?
My high-school-aged daughter doesn’t do much trick-or-treating anymore, but she still needed a costume for Halloween parties. When we asked her what she wanted to be, she said, “I’m going as somebody from the 1990s.” Besides making my wife and me feel old, it was a reminder that once in a while even some of the oldest trends come back into style again.
Some of our country’s oldest structures are defined by their use of exposed wood structural elements—think pioneer homesteads and Lincoln’s log cabin. Eventually, these features went out of style, covered up with plaster, wallpaper and paint. Then, 100 years later, the Craftsman era brought these elements back, with exposed beams, tongue and groove ceilings and wood paneling once again taking center stage.
When it comes to modern high-rise structures, however, concrete, steel and glass have long dominated. That may be starting to change. The move towards more sustainably sourced materials and practices is leading to a renewed interest in wood.
People not heavily involved in green building are often surprised to learn that wood is often a much more sustainable building material than steel. This is because wood is more readily renewable than concrete and steel. Sustainably sourced wood not only requires much less energy to produce, but it actually captures carbon from the atmosphere, thereby creating a positive impact on the environment.
There’s a whole new generation of engineered wood products that take advantage of rapidly renewable wood, and in some cases, post-consumer recycled wood. When used in conjunction with adhesives, binders and other elements, they are able to produce very strong structural components. In some cases, these structural components have been proven to be as effective as steel reinforced concrete in resisting the types of forces necessary for high-rise buildings. These proprietary products go under a variety of names, such as cross laminated timber (CLT), glue-laminated timber (glulam), Parallam®, etc.
Red Tape and Other Barriers to Adoption
The biggest obstacle to replacing steel reinforced concrete structures with sustainably sourced wood framed structures has to do with building code requirements currently recognized in most jurisdictions.
Somewhat counter-intuitively, heavy wood framed structures are actually more fire-resistant than steel reinforced concrete structures, which require extensive additional fireproofing materials. Fire tests show that both solid wood and engineered wood heavy timber elements form an initial char layer that protects the structural integrity of the wood’s core from further damage.
So, if heavy wood framed buildings are able to perform structurally in a similar fashion as steel-reinforced concrete buildings, and if they’re able to provide similar fire-resistive protection capabilities, why don’t we see more heavy wood framed buildings over four stories?
The answer appears to be a combination of factors. For one, the construction industry as a whole tends not be an early adopter of new practices. For another, there hasn’t been significant market demand for higher performing buildings using more sustainably sourced material such as wood.
Will recent tariffs on steel imports shift demand toward engineered wood products sourced from properly managed North American forests? Would this in turn apply pressure to code development and enforcement bodies?
To answer these questions, I reached out to the American Plywood Association (APA), a trade organization that includes engineered wood products. Karyn Beebe is regional manager for APA’s Field Services, a LEED Accredited Professional and respected expert on the technical and sustainability aspects of the latest generation of wood structural elements. Here is what she had to say:
“Regarding tall wood buildings, there are some exciting changes in International Building Code (IBC) development. As you may already be aware, there have been several code change proposals for the 2021 IBC that would allow wood structures up to 18 stories in height. These code changes passed at the code hearings in October 2018. The International Code Council (ICC) membership is currently weighing in online for the final vote. That would address the fire and life safety provisions. There will also be code changes proposed for the structural provisions of the building code in 2019.
“California typically adopts the IBC as our model code, so the assumption can be made that these changes would go into effect here as well. Until these code changes become part of our state code, designers are currently allowed to propose a taller wood building per the alternate means and methods provision of the code.”
In late-December, shortly after Beebe shared her insights with me, Construction Dive published an article offering the following update:
“The ICC has released the preliminary results of its last online governmental consensus vote, and, pending certification of the results, the package of 14 new tall wood construction code change proposals will be incorporated into the 2021 International Building Code.
“Eleven of the proposed changes were debated at the ICC’s public comment hearings this past October at the council’s conference in Richmond, Virginia, and subjected to online voting. Three, according to a spokesman for the American Wood Council, were approved through the consent agenda at the conference.”
I also discussed this topic with Xpera Member Scott Riffenburgh, who is a construction project manager specializing in building science and energy efficiency.
“Introducing changes to traditions in the building industry typically creates controversy, and it can take a long time for the building industry to accept new methods and materials,” he said. “Builders like to use tried-and-true methods and materials, because they want to minimize the risk of construction defect claims.”
He explained that changing building codes can take years. Even when universal code standards like IBC allow for changes, getting jurisdictions to embrace them can be challenging, particularly for those already dealing with overburdened staff or financial constraints. On top of that, fire officials are not exactly rushing to embrace the concept of tall buildings made of wood.
Steel and concrete trade organizations are also weighing in against these code changes, with seasoned lobbyists and big wallets. They claim wood is less fire-safe and less durable than their products, and that their recycling processes are making steel and concrete more sustainable.
“Innovations in building science are happening faster and faster, but acceptance of new practices in the real world can often be measured in generations,” concluded Riffenburgh.
Besides the tariffs factor, there are other economic advantages to taller wood structures. Several new projects in the United States have recently been built, or are currently in the design or construction stages, that may influence the shift towards adoption of taller wood structures as more economic performance data becomes available.
A truly pioneering project that was recently completed in Portland, Oregon, was featured in a case study by the Urban Land Institute (ULI). The project, known as One North, was a collaboration between two developers, and included three buildings on three adjoining parcels. Comprised of 88,857 square feet of office, 15,712 square feet of retail, with a 14,000 square foot courtyard, the project makes wood a prominent feature in its architectural and structural design. Of course, Portland is a well-established source of wood, so much of the wood used for the project came from local forests. Everything from the exterior cladding to timber ceilings, as well as the glulam beams, 2x6 framing and plywood shear walls, all came from carefully selected and well-managed lumber stock.
Due to the project’s reliance on super-insulated building envelopes and fluid-applied continuous waterproofing, thermal bridging and risks of water intrusion are greatly reduced from typically constructed buildings. The end result is an impressive 50% reduction in energy use from similarly sized buildings of the same general occupancy. The total development costs ranged from $247 per square foot to a high of $340 per square foot. In the ultimate test of viability, the project is having no trouble attracting fast-growing creative tenants and has been lauded as a model for future development projects by including a variety of project stakeholders (including the public) throughout the process.
One of the developers on One North already has two additional high-rise heavy timber projects in the works, pending the necessary approvals.
Not Always Easy Being Green
The use of advanced engineered wood products doesn’t come without risk. In fact, one of the greenest buildings ever built in the United States, according to the USGBC, was rendered in need of significant repairs and remediation.
The Philip Merrill Building, built by the Chesapeake Bay Foundation in Annapolis, Maryland, was one of the first buildings to be LEED Platinum-Certified for new construction. The building made extensive use of Parallam® engineered wood components for both structural integrity and aesthetic design. At the time, it was considered a novel use for such a product, as there had not been extensive research about the ability of Parallam® to perform when exposed to exterior elements.
Due to apparent miscommunication between various manufacturers, suppliers and installers, the Parallam® beams that were exposed to the exterior were not properly waterproofed. This allowed water to penetrate the interior of the beams and led to significant loss of structural integrity. In a lawsuit filed by the organization, they stated: “The structural integrity of the project is in jeopardy and the building is now at risk of collapse.”
As with every new – or renewed – interest in a building material or practice, certain basic principles still apply. Established design and construction practices become established through extensive testing and proven performance. Designers need to establish clear criteria for structural and building envelope integrity and should always verify the compatibility of various products being specified.
Lastly, when in doubt, make sure you have the right expertise on tap so that you can readily access the knowledge necessary to reduce risk on your current and upcoming projects.