Completed in March 2019, Allianz Field is a 346,000-square-foot soccer stadium located centrally between Minneapolis and St. Paul, Minnesota. The project was executed by Populous, Walter P Moore (WPM), Mortenson Construction, and FabriTec Structures, and it features a facade of woven fiberglass clear-laminated with polytetrafluoroethylene (PTFE)—effectively a tensile membrane capable of shielding the audience from the elements while transmitting twice as much light as other PTFE membranes.
According to the design team, the client initially approached Populous and Walter P Moore to produce a stadium with a translucent facade. The group was aware of a clear PTFE laminate being developed by French manufacturer Saint Gobain—now known as Illuminate 28—and facilitated the shipment of moderately sized samples from the company. These samples were used to construct a 6-by-6-foot mockup with the material to gauge its tensile and lighting qualities. The design and construction of the stadium occurred as the facade material was being developed.
ConsultantWalter P Moore
LocationSt. Paul, Minnesota
PTFE-coated fiberglass membrane suspended over steel structural system
The enclosure system of the stadium consists of three interconnected layers: the exterior skin of PTFE-laminated fabric, a secondary backup system of steel driver pipes and armatures, and a circular colonnade of steel columns.
In abstract terms, this enclosure system sounds simple enough. However, unlike rigid cladding materials, the tensile strength of fabric is ultimately determined by the 3-D shape it is stretched into. “We never knew if our fabric shapes would work or not from an engineering standpoint until after the design was complete,” said Populous associate principal Phil Kolbo. “To achieve the design, Populous and WPM had to set up a cohesive process that could design, test, and modify the supporting steel quickly and iteratively to satisfy both the design and engineering requirements of the skin.”
In total, over 90,000 square feet of fabric wrap the stadium. Due to budget constraints, the design team had to maximize the spans between structural components. Utilizing Rhino and Grasshopper 3-D imaging software programs, WPM created nearly 50,000 analysis elements to locate sites where the fabric was overstressed. This information was then exported from Rhino to Tekla software and delivered to the steel fabricator.
“Once we had a fabric and driver pipe design, then it was supporting the process throughout getting the owner, Mortenson, and FabriTec comfortable with the material and construction process,” said Walter P Moore principal Justin Barton. “It started in February 2016 and went all the way through FabriTec’s final installation and punch list in late 2018, nearly 24 months of continual conversation.”
Populous Associate Principal Phil Kolbo, Walter P Moore Project Manager Justin Barton, Mortenson GC Project Engineer Nate Weingart, and FabriTec Structures Executive Vice President Tom Wuerch, will be joining the panel "Stadium Rising: The Complexities of Allianz Field’s Woven PTFE Facade" at The Architect's Newspaper's upcoming Facades+ Minneapolis conference on July 24.
On June 25, Facades+ is returning to Boston for the fourth year in a row. The conference, organized by The Architect's Newspaper, is a full-day event split between a morning symposium and an afternoon of workshops led by top AEC practitioners. Leers Weinzapfel Associates (LWA), a Boston-based firm with projects nationwide, is co-chairing the conference.
Panels for the conference will focus on the changes underway in Boston, ranging from new educational structures, the city's new tallest residential building, and historic preservation projects.
Participants for the conference's symposium and workshops include Behnisch Architekten, Knippers Helbig Advanced Engineering, Pei Cobb Freed & Partners, Bruner / Cott, Arrowstreet, Consigli Construction, Walter P. Moore, Autodesk, Atelier Ten, Harvard GSD, the Wyss Institute, and Okalux.
In this interview with The Architect's Newspaper, LWA's designer and business development representative Zhanina Boyadzhieva and associate Kevin Bell, the conference co-chairs, discuss their firm's growing body of work and the developmental trends within the city of Boston.
The Architect's Newspaper: Boston is known as a relatively quiet city with a predominantly low-slung skyline. How is current development reshaping that identity and what does it mean for the future?Zhanina Boyadzhieva: Boston is indeed a “quiet” city, but it is also a hub of innovation and creative thinking. In the past few years, we have observed dynamic design work, largely by local firms, on several fronts: 1) creative re-envisioning of historical landmarks through readaptations and additions such as Smith Center at Harvard University and Congress Square in downtown Boston 2) careful insertions of new landmarks in the skyline such as One Dalton 3) fast development and growth of existing or new resilient neighborhoods such as Harvard’s Allston campus. Each design solution addresses unique urban conditions and entails holistic thinking about city planning, resilience, and sustainability, coupled with a sense of function, form, materiality, and human experience.
Naturally, facades combine all of these considerations and become dominant players in the reshaping of cities. The diversity of approaches we observe—controlled material juxtapositions of old and new, sculptural form-making, and playful screening strategies—are testaments to ongoing design experimentations here. There is a search for new methods to address creative reuse, high performance, material fabrication, and user experience.AN: The city possesses one of America's largest concentrations of brutalist buildings, as well as large historic districts. How can Boston embrace its heritage while moving forward?Kevin Bell: The rich building history of Boston, including modern landmarks like City Hall, and its brutalist companions make for wonderful urban fabric for intervention and a great place for an architect to practice. This history should serve to elevate our expectations for new buildings and major renovations in the city. The recent warming to Boston’s brutalism, its strong geometry and bare materials, is welcome, encouraging designers to consider rather ignore these local icons.
It presents the opportunity to consider adaptation and re-envisioning through sustainability’s lenses, the human experience, and materiality. If we can dramatically improve the energy efficiency and human use in these sensitive historic buildings, we can achieve the same in new construction and create a model for continued improvement.
AN: What innovative enclosure practices is LWA currently executing?KB: As a firm, we have a legacy of designing efficiently in an urban context. Often, our site is an existing historic building or a tightly constrained sliver of land, or sometimes, there's no site at all. This fosters a sensibility within the studio toward compact volumes, materially efficient, with taut fitted skins, a practice that serves us well as we work to make evermore energy efficient and sustainable buildings. We're also redefining our performance expectations around our clients' commitments to energy efficiency, many of whom have established operational carbon neutrality as their aim by mid-century. The enclosures we design today will be part of that efficiency equation. They must be considered to be part of a carbon neutral organizational environment as a performance baseline above simple compliance with today's codes or target certifications. Envelope performance, especially the use of innovative glazing materials, is a logical extension of the way we think about reactive, efficient space and energy efficiency targets in building enclosure design.
Our Dartmouth Dana Hall renovation and addition, under construction now, is an example of this process and practice. We worked closely with the college to define a program for building reuse around its energy use reduction targets that dramatically improved envelope efficiency. Through the design process, we worked with our design and construction partners to continually refine the design while holding to incremental improvement in energy efficiency at each step; our modeled efficiency improved even as we moved through cost reduction exercises. The result is a highly insulated building, triple glazed throughout, with a thermally improved, south-facing glass curtainwall system combining vacuum insulated high-performance glass modules with integrally solar shaded, triple glazed vision glass as part of a building with a predicted energy use index (pEUI) in the middle twenties before the introduction of site renewables.
AN: Which materials do you believe are reshaping facade practices?ZB: Materials are the agents of larger design strategies shaping the practice such as resilience, sustainability, and human experience. The aim to rethink and cherish historical buildings, for example, leads to a careful layering of existing and new materials that contrast and simultaneously enhance each other. Heavy textured concrete at the Smith Center is supplemented by light and open transparent glass, green walls and warm wood. Traditional brick block at Congress Square is juxtaposed with a floating glass box on top of sculptural fiber-reinforced plastic panels.
On the other hand, the vision to create new landmarks that celebrate and reshape the Boston skyline result in the careful sculpting of distinctive volumes as in One Dalton, a tall glass skyscraper with careful incisions of exterior carved spaces for human use. Finally, the goal to produce energy efficient but playful envelopes leads to a game of patterns composed of an inner insulated layer with an outer wrapper of perforated metal screens or angled aluminum fins. Each choice of material and its manipulation reflects a larger vision to create a unique experience in the city.
Further information regarding Facades+ Boston can be found here.
On April 4 and 5, Facades+ is returning to New York for the eighth year in a row. Organized by The Architect's Newspaper, the New York conference brings together leading AEC practitioners for a robust full-day symposium with a second day of intensive workshops led by manufacturers, architects, and engineers.
Doriana and Massimiliano Fuksas, and Toshiko Mori are respectively leading the morning and afternoon keynote addresses for the symposium. In between the keynote addresses, representatives from Renzo Piano Building Workshop, Permasteelisa, Cooper Union, Gensler, Heintges, Atelier 10, Transsolar, Walter P. Moore, Schüco, Frener & Reifer, and Behnisch Architekten, will be on hand to discuss recently completed innovative projects.
New York-and-Frankfurt based practice 1100 Architect is co-chairing the conference. In anticipation of the conference, 1100 Architect's Juergen Riehm sat down with AN to discuss the firm's ongoing work, the conference's program, and trends reshaping New York City's built environment.
The Architect's Newspaper: It is safe to say that New York City is undergoing a tremendous period of growth. What do you perceive to be the most exciting trends within the city?Juergen Riehm: You’re right; New York City is undergoing big change and growth. I would say that one of the big drivers of that change—and one of the exciting trends—is the investment in the city’s public spaces. There has been such transformation along the waterfronts and in parks across all five boroughs, and that has really catalyzed growth. We have worked with several city agencies for many years and in different ways, including with the Department of Parks & Recreation, which has been an exciting partnership, contributing to these changes. One of the projects we currently have in design for NYC Parks is a new community center in East Flatbush, Brooklyn. There, we are designing a 33,000-square-foot community center. The facade will perform in a number of ways. Since it is a community center, we want it to be as open and transparent as possible, and it also needs to be robust and durable. The building is on track to meet the city’s new sustainability standards LL31/32 and LEED Gold.
There has been so much attention on new large-scale developments like Hudson Yards or the supertall towers in Midtown, but one of the other exciting trends right now is the renewed attention on optimizing the performance of existing buildings. It is something we will address during Facades+ NYC, but there is great work happening now on restorations of historic buildings—at the Ford Foundation or the United Nations, for example—that not only addresses decades of wear and tear, but that also brings these structures up to full 21st-century performance standards.
AN: 1100 Architect is based in both New York and Frankfurt. What are the greatest benefits of operating a trans-Atlantic practice?JR: Our practice has always been deeply rooted in New York—just as it has also always had an international footprint. From our earliest days, we delivered projects overseas, so it seems like part of 1100 Architect’s DNA to have an ongoing dialogue with other geographies. We launched our Frankfurt office about 15 years ago, and, as you suggest, it does bring benefits. In general, we find that it has a reciprocal sharpening effect, with each location informing the other with different materials, technologies, and delivery methods.
AN: Which projects are 1100 Architect currently working on, or recently completed, that demonstrate the firm's longstanding demonstration of sustainable enclosures?JR: Well, the NYC Parks community center in East Flatbush is a good example. It’s an exciting project in many ways—including the fact that we are designing it to the City’s new LL31/32 sustainability standards. In every way, we are really pushing for optimal performance, and the high-performance envelope plays an integral role toward that end. We were recently awarded a contract with the U.S. Department of State, so we are poised to begin working on diplomatic facilities around the world, so the safety and security of facade systems will be a paramount consideration. In Germany, we are renovating a 19,000-seat soccer stadium and adding a new training facility, using an innovative and high-performance channel-glass facade. We recently completed a Passive House–certified kindergarten there, too, which involved a high-performance facade.
AN:Are there any techniques and materials used in Germany or the EU that should be adopted in the United States?JR: In Germany, I find that there is a more closely integrated relationship between government, the building industry, and the architectural profession. With environmental standards, for example, the goals set by the government are quite ambitious, and it has resulted in a closely integrated process of meeting those goals. In this moment of deregulation in the U.S., it seems like a good time to consider the value of the government’s role in moving toward energy efficiency.
AN: Where do you see the industry heading in the coming years?JR: By necessity, I see it moving toward higher standards of energy performance. Climate science is calling for it and the marketplace is increasingly looking for it, so the architecture and building industry will need to deliver. And as I mentioned at the start of this conversation, I also think there will be a lot of focus on updating existing buildings to enhance performance.
Further information regarding the conference can be found here.
Designed with community and connectivity in mind, Populous has recently completed an amphitheater and flex field adjacent to the Jacksonville Jaguars’ professional football stadium. The project, named Daily’s Place, is the first amphitheater integrated with an NFL stadium in the country. With the grounds of the stadium active only a handful of times per year, the project is a response to a desire to activate the stadium area beyond football season with training events, concerts, festivals, and more.
Two column-free large event spaces—composed of more than 80-percent fabric and steel—were delivered under a close collaboration between design and engineering teams. The entire facility is covered under one all-encompassing PTFE roof system manufactured by advanced polymer technology company Saint-Gobain. The composite membrane, called SHEERFILL, is made of fiberglass and polytetrafluoroethylene (PTFE) typically used as a permanent tensioned membrane structure in sports, transportation, retail, and specialty markets.Design, engineering and fabrication teams used the software in an unconventional way to blur the lines between design and detailing with construction and fabrication modeling. Populous consulted with Walter P. Moore, an international A/E firm, who provided envelope and facade engineering expertise. Erik Verboon, Principal at Walter P. Moore, said the project was very fast pacing, involving a "fluid" digital process. "This could have only been completed under a close collaboration with Populous and a digital workflow that we both harnessed." Design and construction models were shared back and forth between the design and engineering teams, involving an iterative series or Rhino and Grasshopper models. While Populous managed the formal strategy of the project, Walter P. Moore worked through model analysis and optimization that involved engineering and form-finding techniques.The facade involves a series of "V" shaped perimeter columns set inboard from the exterior envelope. The materiality of the skin began as polycarbonate panels, but evolved into an open mesh PTFE fabric to save steel tonnage that the smaller more rigid polycarbonate panels would have required.Above, an undulating roof of Daily’s Place passively cools the interior of the facility by controlling air movement. The resulting “roofscape” integrates LED lighting to highlight its wavelike form, introducing a customizable aesthetic element that can be adjusted dependent on programming.As a result of the scheduling of the project, ordering of the steel framework was on a critical path, however, the sizing and detailing of the steel was highly dependent upon the configuration of the PTFE fabric. Due to this, Verboon said the engineering of the system relied on "coupled models" which dynamically take both structural requirements of the PTFE fabric and steel framing into consideration, producing an optimized, efficient design. "The steel was based on loads of the fabric, and the fabric was based on the geometry of the steel. The two materials were intrinsically linked."
(Courtesy Populous).One of the most challenging aspects of the detailing of the building envelope was the location of the roof membrane, which sits below long span trusses. The positioning of the membrane produced translucent ghosted effect, softening the visual impact of the structure, but resulted in detailing challenges with necessary penetrations from steel rail supports and the perimeter structure. At these columns, a unique "top hat" detail, involving a circular flange surrounding a steel drum, developed to ensure a watertight connection.
Thanks to the city's humid subtropical climate, facade designers and fabricators face a special set of challenges in Houston. Unchecked, steady sunshine and high temperatures can permeate the building envelope, leading to a heavy reliance on mechanical cooling systems. Meanwhile, Houston's Gulf Coast location makes it vulnerable to tropical storms.
Sanjeev Tankha, principal and director of facade engineering at Walter P. Moore, argues that the solution to performance issues including solar gain and wind lies in a holistic approach to facade design. "All aspects of building envelope performance—from materials science to building physics analysis, structural analysis, research and development, waterproofing and weatherproofing, longevity and life cycle analysis—must be given a platform to engage effectively in the design process," he said. "Our industry must come to terms with and take on the challenge to respond effectively to the elements of solar heat and wind mitigation."
Tankha will share his experience responding to the local climate next month at Facades+AM Houston. A half-day spinoff of the popular Facades+ conference series, Facades+AM brings regionally-specific discourse on high performance building envelopes to AEC industry professionals, students, and policymakers.
In the real world of building design and construction, observed Tankha, environmental performance is regularly sidelined in favor of other concerns. "Performance of the building skin, in any given project, is often trumped by financial pressures to the detriment of overall building performance," he said. "I would like to see more commitment from AEC stakeholders to make performance issues a core value in our work." The key, he explained, is making performance a priority from the get-go. "The early design work needs to embed these values in the development so they are not add-on features," said Tankha. "This is a philosophical debate that is held on every project, and many times building performance comes out on the losing side."
In Tankha's experience, less can be more when it comes to addressing solar gain and wind. "I always encourage the use of passive technologies and passive building systems first before the overlay of active systems," he said, pointing to historical strategies including building form and orientation. "I see some of that design philosophy coming back and now coupled with advancement in materials, coatings, and efficient mechanical systems, we have a palette for a holistic approach towards exploring effective solutions."
To hear more from Tankha and other building envelope specialists, register today for Facades+AM Houston.
It appears our friends at engineering firm Buro Happold, which just moved their offices to Downtown Los Angeles, are experiencing some of their own moves. Chief engineers Greg Otto and Sanjeev Tankha have taken their talents to Walter P. Moore, a Santa Monica firm hoping to expand their design expertise and research capabilities. In other moving news, after ten years wHY Design’s founding partner Yo Hakamori has left the firm for DesignARC. And over in New York our friend Dung Ngo has announced he’s leaving Rizzoli. No word why at this point, but according to Ngo the parties are leaving “on the very best of terms.” If only all breakups were as amicable.