Zipper trusses, a structural system developed by faculty at UMass Amherst
Alex Schreyer Zipper trusses, a structural system developed by faculty at UMass Amherst

“From the beginning, we knew that the Design Building would be a teaching tool,” says Andrea Leers, FAIA, a principal at Leers Weinzapfel Associates (LWA). “Even in the interview, we talked about the idea that this kind of building needs to be a part of the pedagogy of the school.”

What Leers did not know was that the facility, which brings together the architecture, landscape architecture, and building and construction technology programs at the University of Massachusetts Amherst, would evolve into the first mass-timber structure on the East Coast, and become the first project to use several cutting-edge building technologies, including a “zipper truss” and a composite floor system developed by the school’s faculty.

Opened in January 2017, the 87,000-square-foot academic building is located on a sloping site at what LWA principal Tom Chung, AIA, calls a “knuckle” between the campus’ historic Stockbridge Way and the more modern Haigis Mall. Clad in aluminum panels, the building’s main volume, which houses offices, studios, and lab spaces, coils around an enclosed, two-story central commons, climbing from three stories at its east end to four stories at its west.

Section through the UMass Amherst Design building. The zipper trusses are featured prominently in the central commons.
Section through the UMass Amherst Design building. The zipper trusses are featured prominently in the central commons.

As a teaching tool, it embodies contemporary ideas: the importance of interdisciplinary collaboration, and the urgency of climate change. The former is evident in the building but also in the design team: from the beginning, the project was led by LWA and Stephen Stimson Associates, a landscape architecture firm in Cambridge, Mass., with heavy input from instructors and department heads.

The building’s physical and spiritual heart is the commons, which Leers describes as “a three-sided courtyard [that] spills out through the café, through the entryway, down into the main campus, and invites the campus in.” The design of the day-lit atrium preceded almost every other aspect of the design “based on the fact that these folks had never been together before,” she notes.

But the commons also presented a structural challenge. As the building’s footprint morphed into a quasi-trapezoidal shape (in response to the site’s topography), the 84-foot-long commons became increasingly complex in form: 56 feet wide at its west end and 33 feet wide at its east. On top of that, literally, the building needed to accommodate skylights and an inhabitable rooftop garden. “This was a real structural challenge,” Leers says.

Then came the switch to timber. LWA was more than halfway through design development with a steel structure when the university decided to pursue a heavy timber frame. It was a major victory for the building and construction technology program, which for the past 10 years has focused on wood technology. Faculty members Alex Schreyer and Peggi Clouston, both of whom had spent time at the University of British Columbia, arguably the epicenter of advanced timber design in North America, pushed for the building to incorporate as much wood as possible, using life cycle cost assessments to make the case that it was the most sustainable structural option. “Everybody agreed,” Clouston says. “But money speaks.”

The concern, Clouston says, was that the new technology would come with a hefty price tag, especially given the lack of local expertise with materials like cross-laminated timber (CLT). Those concerns were eventually overcome when a former Massachusetts representative secured $3 million in additional state funding and got the building listed as an official demonstration project.

Though LWA also lacked design experience with CLT, the firm embraced the change. “We knew this was a chance to learn about something important,” Leers says. Clouston called Equilibrium Consulting, in Vancouver, whose portfolio includes many of North America’s most well-known timber structures, which joined the design team alongside structural engineer Simpson Gumpertz & Heger, based in Waltham, Mass.

The Design Building's mass-timber structure will serve as a teaching tool for the campus and greater AEC communities.
Alex Schreyer The Design Building's mass-timber structure will serve as a teaching tool for the campus and greater AEC communities.

Today, the Design Building is one of only two buildings in the U.S. to use timber for every major structural system (the other is the recently completed T3 office building in Minneapolis). In keeping with the building’s pedagogical mission, all its structural systems are exposed: the glue-laminated post-and-beam structure, CLT shear wall cores, composite concrete-and-CLT floor plates, and the custom steel-and-glulam zipper trusses, named for the way they converge multiple structural members to a single point.

The zipper truss solved the structural challenge of the irregularly shaped green-roofed commons. LWA toyed with several other solutions, including some “funky” asymmetrical slab bends, Chung says, but the zipper truss was the “best combination of a dynamic form, architectural consistency, structural efficiency, and cost. It reinforces the overall building column grid, allows for various span lengths while keeping the same form, and highlights the cost effectiveness of the digital fabrication process.”

Each of the seven trusses consists of four tubular glulam struts (9 inches in diameter) and four steel rods (between 1 inch and 2 inches in diameter). The 12-foot-wide trusses range between 7 feet and 9 feet deep, while their lengths vary with the span of the commons. The glulam compression members, which are capped with steel ends, transfer the roof’s structural load to a central steel node that Chung refers to as the “bullet connector.” The steel rods then work in tension to transfer the load to 18-inch-deep glulam beams, which span the width of the atrium and are supported by columns.

Zipper truss detail
Zipper truss detail
Elevation view of zipper trusses from the west looking east, where the atrium is 23 feet narrower
Elevation view of zipper trusses from the west looking east, where the atrium is 23 feet narrower
Detail of the zipper trusses, which utilize compression and tension members to transfer gravity loads to the timber structural system.
Alex Schreyer Detail of the zipper trusses, which utilize compression and tension members to transfer gravity loads to the timber structural system.

Clouston calls the zipper trusses “spectacular” and “a beautiful example” of how forces flow through a building, something she shared with her structural mechanics students on their first day. She will also be teaching students about the building’s composite concrete-and-CLT floors, which use a steel mesh connector plate that was developed by the university’s research faculty. The perforated metal plates are glued into notches routed into the CLT panels. When the concrete is poured on top, the steel plates join the two materials in composite action.

It’s an important lesson for would-be engineers, Clouston says. “It’s been a frustration of mine that here in North America, quite often we’ll build timber structures and pour concrete on top, and just allow the concrete to be dead weight when the concrete is structural and should be engaged,” she says. “That’s what these floors do, and they feel like slab-on-grade under foot. They are solid.”

As sustainable as the timber is, it may be its ease and speed of construction that wins over American builders and real estate developers. Those involved with the Design Building say there are innumerable advantages to building with heavy timber, including a quiet and dust-free construction site. And, thanks to 3D modeling and digital fabrication, “installation time is really quick,” Chung says. For instance, the four 60-foot-tall-by-1-foot-deep CLT panels comprising one of the building's shear-wall cores were lifted and dropped into place with a crane, and anchored to the foundation all in one weekend, Clouston says.

Chung hopes others, besides students, will learn from the Design Building and its form. Most mass timber buildings in the U.S. are relatively simple, rectangular towers. The Design Building, by contrast, is sculptural, with cantilevers and complex volumes.

Overview of the day-lit commons
Alex Schreyer Overview of the day-lit commons

It certainly has attracted attention. The building was included in the “Timber City” exhibition at the National Building Museum (on view through Sept. 10), and Clouston says she has been overwhelmed with phone calls and requests to tour the building.

But there are roadblocks to replicating this type of structure. One is the region’s timber stock, which is lower in quality than that of Washington state or British Columbia, Clouston says. The other is education. “We are woefully behind in having educated engineers in timber design,” she says, explaining that less than half of American universities teach wood as a structural material.

The university hopes to change that model and expand the imaginations of a new generation of students. In fact, Clouston says, part of the Design Building’s purpose is “to be the ambassador of change.”

Note: This article has been updated since first publication to correct that the Design Building was initially planned with a steel structure.