Harvard University’s first hybrid conference center of solid wood and low-carbon concrete is a bold commitment to sustainability.
Designed by the architectural firm Studio Gang, the school’s David Rubenstein Treehouse Conference Center is the first building in Massachusetts to use low-strength concrete at scale, says the project’s joint venture Consigli-Smoot construction management team. The team is finalizing items on the list, including a cafe and first-floor retail space that will be completed in February.
Located in Boston’s Allston neighborhood near Harvard Business School and the School of Engineering and Applied Science, the 55,000-square-foot treehouse opened in October and is one of the first buildings completed on the university’s Enterprise Research Campus (ERC), a mixed-use campus developed by Tishman Speyer with five more buildings under construction.
John Lehane, Consigli’s director/project executive, says the Treehouse required “coordination with other project teams, subcontractors and other stakeholders while providing a unique mass timber structure.”
In addition to navigating more than 1 million square feet of ongoing construction at the ERC, the team managed more than 2 acres of landscape and landscaping work and more than 900 workers on site at peak time.
Riggs carpenters from Consigli’s self-build division, who erected the massive timber structure, attached specialized structural nodes to glulam columns.
Courtesy of Consigli Construction Co. Inc.
Accurate sequencing
The structure’s custom design adds complexity, as its 213 columns, 343 beams and 239 cross-laminated timber panels were sourced “from international suppliers in a precise sequence,” says Lehane, adding that this required “meticulous planning and choreography with Riggs, Consigli’s in-house facility, to ensure the execution of the team without a massive seam.”
The suppliers (Nordik Structures, South County Post & Beam, Hasslacher Norica Timber and Westdek) provided 60,000 cubic feet of lumber, including spruce, pine and spruce cross-laminated timber panels, Alaskan yellow cedar exterior lamination and cladding, and European spruce interior beams and columns.
Temporary bracing towers designed to support each of the 35 unique structural node connections were critical to creating the building’s solid wood columns that branch outward to support its cantilevered upper level.
Courtesy of Consigli Construction Co. Inc.
Branched geometry
While meeting spaces in a conference center are often on the ground floor for easy access, the three-story treehouse conference center is on the top floor, which simulates climbing the treehouse steps and stimulates creativity, says design architect Jeanne Gang, a founding partner of Studio Gang and the Kajima Professor of Architectural Practice at the Harvard Graduate School of Design.
Studio Gang worked with Henning, Larson, Scape and Utile on the master plan that will transform the vacant former industrial site on the Harvard property into a vibrant 900,000 mixed-use community with residential, office and lab space, along with retail and restaurants.
The building’s treehouse shape expands as it rises “to accommodate the programming needs of the space,” says Michael Shearer, associate structural engineer at Arup, who in collaboration with Studio Gang provided multidisciplinary engineering, including structural, mechanical, electrical and plumbing engineering, acoustics and sustainability services.
“The branched mass timber columns lean outward to create this form, resulting in a push and pull on the second and third floors that are resolved through the building’s diaphragm,” he says.
Arup teamed up with South County Post and Beam, the fabricator, and Aspect Structural Engineers, the mass timber design support engineer, to strengthen the diaphragms to deliver lateral forces to the building’s cores, Shearer says.
The complexity of the single-branch geometry required the team to “erect 35 temporary shoring towers to support each structural node until the diaphragm was locked and the structure was fully lifted,” an innovation developed in preconstruction with Aspect, Lehane says.
As with other solid wood projects, this project required acoustic engineering to adjust for sound reflection that the human ear processes as reverberation. This helped achieve “speech clarity and sound isolation between quiet and active areas,” says Arup associate director Alban Bassuet, who added that “Arup’s SoundLab auralizations guided the team to a solution that used 50% ceiling absorption in meeting rooms and similar wall coverage in the atrium to control reverberation and crowd noise.”
Through auralization, acoustic engineers create a reproduction of a soundscape using speakers (or headphones) in an acoustically controlled environment like Arup’s SoundLab, Bassuet notes.
Crews installed protective cladding on the glulam columns and CLT deck during project construction at an active and logistically challenging site.
Courtesy of Consigli Construction Co. Inc.
Sustainable Design
The treehouse design combines several sustainability strategies to optimize the building’s performance and will help Harvard move toward its goal of becoming fossil fuel-free by 2050, while meeting the city’s building emission reduction requirements. The structure incorporates natural lighting and self-shading to reduce energy use and bioswales that work in combination with a roof system to retain and reuse rainwater and stormwater runoff, Studio Gang says. The treehouse also connects to the Harvard District Energy Facility, which provides the building with heating, cooling and electricity.
In addition to using low carbon mass wood, Boston Sand and Gravel supplied 206 yards of concrete made from ground glass pozzolana, a cement replacement made from locally sourced waste glass containers and produced by Urban Mining.
“Ground glass pozzolans (GGP) and slag replaced up to 70% of cement in concrete mixes to achieve significant embodied carbon reductions from typical mix designs,” says Michael Schearer, associate structural engineer at Arup.
Harvard’s hope is that its use of innovative climate-friendly materials such as GGPs will inspire other institutions to do the same. “We’re really trying to scale a healthier and more sustainable supply chain, using our campus and capital projects as a testbed to translate research and multidisciplinary ideas into practice for results that can scale beyond Harvard,” Heather Henriksen, Harvard’s chief sustainability officer, told the Boston Globe.
All materials and finishes used to build the project met the requirements of Harvard’s Healthier Building Academy, exceeding Living Building Challenge standards, says the Consigli-Smoot project team. Consigli worked with Studio Gang along with Perkins & Will Architects, the Harvard Office of Sustainability and Arup to achieve the project’s sustainability goals.
Half a mile away, Shawmut Design and Construction is also building a massive wood project for Harvard. Nearly 75 percent complete, the university’s American Repertory Theater is set to open in early 2027.
