Is spatial laminated timber the future of sustainable construction?

Concrete is ubiquitous for good reasons, including being among the strongest building materials. It also comes with significant drawbacks: The production of cement, a key ingredient in concrete, creates approximately 8% of global greenhouse gas emissions. To offset this, building materials companies are adopting circular economy models to accelerate low-carbon and carbon-neutral products. There are similar challenges—and responsibilities—for the modern steel industry. Although steel is recyclable, steelmaking generates up to 11% of global greenhouse gas emissions. To counter this, the steel industry has worked to proactively reduce emissions and waste, decreasing its environmental impact.

And then there’s timber. Deforestation causes 15% of global greenhouse gas emissions, but wood that’s harvested from sustainably managed forests actually absorbs more carbon dioxide from the atmosphere than it emits. That’s because trees don’t just ingest carbon dioxide; they also store it. When trees are felled for timber, the carbon inside them stays there until the wood is burned or decays, making timber one of the most sustainable building materials.

But timber is neither infinite nor clean. Trees can be replanted, but it takes years or decades for forests to regenerate. And though trees sequester carbon, timber production, transportation, and construction still emit it.

To balance timber’s environmental benefits and impacts, designers and builders interested in sustainability face an awkward paradox: How does one simultaneously use more timber but also less?

Skidmore, Owings & Merrill (SOM) might have an answer: spatial laminated timber, or SLT. At scale, both the material and the research-driven process that created it could help the architecture, engineering, and construction industry reach new heights of sustainability and innovation.

SOM created SLT as part of an advanced technology research project for the 2021 Chicago Architecture Biennial. Developed with students from the University of Michigan’s Taubman College of Architecture and Urban Planning, SLT was inspired by cross-laminated timber (CLT), an engineered wood product made by gluing together layers of kiln-dried lumber in a crisscross pattern that gives it structural strength and integrity. Unlike CLT, however, SLT uses smaller, precision-cut 2x4s woven together like fabric via interlocking timber joints, then layered densely in places needing more structural support and sparsely in places that don’t.

“One of the challenges with a standard CLT system is the size of plank that’s required and the amount of time and space it takes to grow trees at that scale,” says SOM Design Partner Scott Duncan. “With a smaller piece of wood, you’re able to grow it more quickly, and you can utilize less desirable parts of the tree that are often thrown away. You could even use salvaged pieces of deconstructed buildings.” By using small and salvaged pieces of wood, SLT can reduce timber consumption by 46% compared to conventional timber panels, SOM estimates.

A secondary benefit, according to Duncan, is that SLT allows for better placement of building services such as ductwork, lighting, and sprinklers. Normally, those have to be placed below structural wooden beams, which forces walls to be built taller than they otherwise might be. With SLT, building services can be embedded within timber instead of layered below it, which means buildings can achieve the same interior ceiling heights with shorter exterior walls.

“After the structure, a lot of the embodied carbon in a building comes from the exterior cladding,” says Duncan, who cites glass and aluminum as typical high-carbon cladding materials. “So to the extent that you can reduce the height of the exterior wall, you can reduce the amount of material that goes into it.”

Technology is a key enabler of SLT, according to Tsz Yan Ng, associate professor of architecture at the Taubman College of Architecture and Urban Planning. First, spatial analysts use computational modeling to determine an optimal layout—that is, how many layers of SLT latticework are needed in order to maximize structural integrity while minimizing materials. Then, fabricators in a laboratory use a CNC machine to robotically shape and cut precise wood pieces to be assembled onsite.

“Technology is never about any one singular solution. It’s about processes and modes of working,” Ng says. “Here, we’re using it to elevate this ubiquitous material that is so popular in North American construction and to rethink it in a way that saves material when we use it.”

To demonstrate the benefits of SLT, SOM and Taubman designed and built a full-scale prototype of a single-story structural framing system used in midrise, fire-resistant construction: a timber pavilion they call SPLAM—short for spatial laminated timber.

Comprising 412 SLT panels made from 912 pieces of wood, the SPLAM pavilion stands on the campus of EPIC Academy, a public charter high school on Chicago’s South Side. Completed in September 2021, it initially hosted a series of events for the Chicago Architecture Biennial but is now being used by EPIC as an outdoor classroom and performance space.

“Instead of just creating a proof of concept that would end up in a landfill, we wanted to make a pavilion that would actually be used,” says Ng, who cites as inspiration the Freedom Schools of the 1960s—temporary, alternative schools organized by leaders of the Civil Rights Movement that offered spaces for Black students and parents to become engaged voters and citizens. “We were working at the height of the pandemic, when it was actually safer to be outside than inside, and during the period of Black Lives Matter,” Ng says. “Freedom Schools were informal gatherings where education was about civic participation and growing as a community, and we saw an opportunity to connect to that history by creating an open and flexible learning space.”

Although students at EPIC are using the SPLAM pavilion, students at Taubman helped create it, according to Ng, who says Master of Architecture students spent an entire academic year conceiving and testing SLT prototypes in close collaboration with SOM engineers.

SOM used Autodesk Revit to track the entire design: The drawings were used to assemble every part of the project and document every element in the building. All of the modeling done in Revit was communicated to the contractor/builder to expedite construction. Finally, the layout for the 2x4s required highly articulated joints and predrilled screw holders located in precise locations; this work was done in Autodesk Dynamo, which was also used to create the animation that was sent along to guide the contractor. Once the concept was proven, the design finalized, and the scripts programmed, fabrication and installation took just a week each.

SPLAM’s immediate benefit as a school and community space is obvious. What’s most significant, however, is its long-term transformative potential: At scale, the SLT system used in SPLAM could fundamentally change the AEC industry.

“Particularly in the era of planetary crisis that we’re in, we have to recognize the impact that our cities and buildings have on the environment and do what we can to reduce it,” Duncan says. “A project like SPLAM is a tiny piece, but it’s intended to have an amplified impact on the culture of construction.”

Large impacts begin with small steps, according to Duncan, who says SOM invests in research-driven projects like SPLAM because they drive real improvements in design and construction, not just for the attention and accolades.

“We talk a lot at SOM about incremental innovation,” Duncan says. “What I mean by that is learning from what’s come before, then building upon it. Because we’re often working at a large scale on very complex projects, there’s a need to innovate by relying on our own past experience.”

Research-based projects are opportunities to create experience where there is none—to build the first step in what might eventually become a grand staircase to new levels of efficiency and productivity. In that way, proofs of concept can end up supporting real, commissioned work.

But it doesn’t happen overnight. To transform innovation into application, firms that sponsor research must invest in the infrastructure to scale it.

“A surprisingly important factor in applying new ideas is the role of the contractor,” says Duncan, who suggests “pressure testing” new ideas with construction partners to determine their feasibility for the construction workforce. “It’s one thing to make something in a lab under the right conditions, but it’s quite something else to do it on a real construction site.”

It’s not enough for a new innovation to work. When real dollars from paying clients are at stake, it has to work as quickly and affordably as conventional methods and materials.

“To implement new ideas at a larger scale, it’s important to understand the building industry as it currently exists,” Ng says. “So a proof of concept is not just a thing; it’s also the process and having a workforce that can deliver on the process.”

To make their visions real, innovators must be willing to take on new roles and responsibilities. Firms that are used to designing, engineering, and building, for instance, must also get comfortable teaching, training, and evangelizing.

“If your goal is to do something that’s never been done, it’s critical to step outside your lane,” says Duncan, who adds that SLT and future innovations like it will help SOM reduce construction costs and carbon. “We try to align environmental efficiency with economic efficiency, and structure—the wooden stud—is one really promising area in which we can do that.”