Filigree & Form

Metal Screen Brings Functional Aesthetics to the Ivy League

By Jordan Scott

The Harvard University Science and Engineering Complex (HUSEC) in Boston is the epitome of German engineering and collaboration, with much of the design techniques and materials originating in Europe. The eight-story, 544,000-square-foot building features three large volumes connected by two glazed atria. It boasts five principal façade types, giving unique identities to the different spaces. Its signature façade features a metal screen fabricated using hydroforming, a world-first in architecture.

Energy efficiency was a major focus of the project, and the metal screen paired with triple insulating glass units (IGUs) helped the project achieve LEED Platinum status. The metal screen reduces the solar heat gain in the summer while allowing beneficial sunlight to pass through the façade during colder months, reducing cooling and heating loads.

Behnisch Architekten, an architecture firm based in Stuttgart, Germany, with a location in Boston, worked with façade consultant Knippers Helbig, also of Stuttgart, façade contractor Josef Gartner—a division of Permasteelisa North America—based in Gundelfingen, Germany, and  limate engineer Transsolar Energietechnik of Stuttgart to design the complex building exterior.

Design-Assist

The HUSEC was 15 years in the making. The design process started in 2006 but was paused in 2009 due to the financial crisis before resuming in 2014. Josef Gartner joined the project in the design-assist phase in 2016. Klaus Reuschle, project director for Josef Gartner, says his team looked at the façade from different angles to determine how best to realize the architectural design.

“The architect was constantly developing the design itself while we were trying to meet the performance specifications and bring the building into reality,” he says. “There was a lot of trust between all parties that we could develop and build something great together.”

The atrium façade design was completely redesigned during the design-assist phase, and Josef Gartner went through trial and error to confirm what was feasible for the metal screen fabrication. Reuschle explains that his
team worked hard to push the limits of what the material could do to achieve the desired result.

“The design-assist process was of critical importance. We were fortunate to work with one of the best façade contractors in the world, Josef Gartner based out of Bavaria, Germany, which is just an hour and a half from our Behnisch Munich office. They thought outside the box from the get-go by introducing us to fabrication techniques outside of the traditional confines of building and construction,” says Michelle Lee, a façade specialist at Behnisch Architekten. “They connected us to Edelstahl Mechanik, a small family business that specializes in making custom stainless-steel components for the automotive, aerospace, and industrial cooking industries. They are in Göppingen in Southern Germany. So, taking this local expertise and extending the technology to this façade was a major focus on the design-assist efforts.”

Five Façades

In addition to the main metal screen façade used on the laboratory portions of the building, the project includes a double height steel stick system for the entrances, a window wall system used for the garden façade, the courtyard façade, and the atrium façade, which includes a large span cable wall with structural shades.

The atrium façade is four stories and hangs on a flat, ¾-inch structural steel beam spanning across the entire wall. Horizontal shading panels on the exterior stiffen the façade and support the beam in taking on the load.

“Due to the sheer size of the program, we used the façade types to give different identities and characteristics to the spaces, so there is a village-like quality of discovery and unfolding of experiences,” says Lee. “The large south-facing atrium multi-story glass façade connects spaces vertically, while others have a more horizontal quality in dialog with the terracing and landscape and, of course, the signature screen façade provides a filigreed tapestry to the large lab spaces.”

Triple Threat

The project includes 151,876 square feet of triple glazing fabricated by Eckelt Glas in Steyr, Austria. The majority of the triple IGUs are composed of 8-mm extra clear, fully tempered glass with a Guardian SNX 60/28 T high-performance coating on surface #2, a 12-mm argon fill with a Chromatech spacer in smooth black, a 6-mm lite of Planiclear annealed glass from Saint Gobain, a 12-mm argon gill with a Chromatech spacer in smooth black, and a 10- mm lite of fully tempered Planiclear glass with a Planitherm XNII low-E coating on surface #5.

“The glass met our thermal, visual light transmittance, solar heat gain, and structural performance specs,” says Lee.

The IGUs have a U-value of 0.13 BTU/h ft² oF and a solar heat gain coefficient of 0.23. Roman Schieber, associate director at Knippers Helbig, says several different glass compositions were used due to different wall types, sizes, and loading.

The typical glass lite was 63 by 149 inches. The maximum size vertically is 63 by 226 inches, used in the entrance façade, while the maximum size horizontally is 143 by 59 inches, used in the atrium façade.

Mindful Metal

“First, we had a high-performance envelope with triple glazing. This established a good baseline for thermal and acoustic performance. Second, the deployment of fixed sunshading reduced peak solar gains by [more than 50%]. This drove down the cooling load for the building so that we could use radiant ceilings to heat and cool the offices, classrooms and teaching spaces. Radiant ceilings are not only more energy-efficient and temper the interior spaces, but provide a more comfortable thermal environment for the users of the building,” says Lee.

To achieve the desired effect for the metal screen, Josef Gartner turned to Edelstahl Mechanik and hydroforming. After wind tunnel, structural and acoustic testing, the project team determined that a 1.5-mm raw thickness would work best to achieve the appropriate durability without making noise on windy days. The raw steel sheets were 30 by 30 inches.

“We used a special metal forming method called hydroforming to fabricate the shading panels to minimize the use of material, lower the cost of production and deliver the façade on schedule. This type of metal forming is not commonly used in architecture. Our project [team] developed the first hydroformed tensile façade in the world,” says Lee.

Reuschle says ten different molds were used in the hydroforming process. According to Schieber, a thin piece of metal was pressed in the mold using a water and oil mixture, then heated and formed in the mold a second time to reduce stress in the material. He says that because the molds cost approximately $30,000 each, the design team was careful not to use too many different molds. The panels were then cut into different shapes and sizes with a 3D laser, creating 28 shading panel types. Thenumber of metal panels used in the project is 12,960, totaling 89,600 square feet.

The waste material left over after laser cutting and perforating the panels was then recycled. Steel was chosen over a composite material because composite is difficult to recycle.

The perforation softens the light contrast between the vision area and the opaque shading, says Schieber, making it more comfortable to look outside. There was an allowance of 100 holes per panel due tomachining costs. Different hole sizes were tested in an acoustic wind tunnel to ensure the façade wouldn’t whistle.

“We put a lot of care into designing the façade from the inside out, [including] how the façade was experienced by the students, researchers, and faculty who will be using the building for many years to come,” says Lee. “Therefore, making the shading screen as light and delicate as possible was our major challenge. To form 12,960 panels out of 1.5-mm metal required a lot of research, and there were a lot of errors and failed prototypes before we perfected the technique.”

A total of 575 vertical pre-tensioned stainless steel rods with a maximum length of 70 feet were used to suspend the metal screen, acting as a cable wall, but on the exterior, rather than interior, of the glass. Large springs are affixed to the top of the building and connected to the rods to take on the façade’s movement and keep it balanced, according to Reuschle. There’s a deadload support at the base of the façade and lateral supports at the slabs.

Installation Interface

Josef Gartner had to consider how to approach the interface of the different types to ensure proper functionality and alignment of the multiple facades used. Reuschle describes the interfaces as the most challenging part of the project, involving hundreds of design hours.

“We developed 3D models, which we verified, due to tolerances, on site with as-built surveys. Installation crews received exploded assembly drawings and a box with all the parts per ‘intersection detail.’ We also had a full-time technical advisor on site. This is a designer who usually is part of the design team in Germany during the shop drawing phase,” says Reuschle. “When we start on site, the technical advisor moves to the project location and supports the local installation crew with their know-how … explains drawings and details, and provides technical support and work instructions. They are the link between the design office in Germany and the construction site in the U.S. As the Harvard HUSEC was so complex technically and we had so many different façade types and intersections, we had two full-time technical advisors on site supporting our installation crews.”

Sun and Shade

Views, daylighting, and shading are inextricably connected, according to Lee. With external sunshading, more glass and glass with higher visual transparency can be used.

“The size of the screen panel module was determined by our goal to provide always an unobstructed aperture of 2.5 feet by 2.5 feet. We also distributed the shallowest panels at sitting and standing levels and put the denser panels out of the site lines,” she says. “Further, the shading panels were geometrically optimized for each solar orientation, so they only shield the façade from the worst offending sun angles and are open to views and daylight from all other perspectives. Finally, the support of the shading structure, designed by our façade engineer Knippers Helbig, was moved to the top and bottom of the façade to attach to the steel ‘superstructure’ of the volumes to minimize visual noise and maximize daylight in the interiors.”

On a holistic level, the design team tried to express the humanistic and artistic side of science and engineering through the façade, which combines advanced technology and engineering with sculptural and sensorial aspects.

“Graduate schools, including Harvard’s, are often called ‘School of Arts and Sciences’—as if they are diametrically opposed. Our façade hopes to bring these two disciplines together,” says Lee. “… Our building sits right at the horizon line on a major regional highway called the Mass Turnpike, which funnels commuters in and out of Boston every day. So, most of the people who see the building never set foot in it. This is why we wanted to have a façade that can connect with people at multiple scales and levels. Depending on the time of day and season, the façade looks completely different since it was shaped by the geometry of the sun.”

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