Behind the Curtain Wall
Three residential buildings with highly innovative facades rise in New York City.
Apartment buildings line the sidewalks of New York City's streets. High or low, old or new, brick or glass, they define Manhattan neighborhoods. Before the real estate bubble burst and demand for luxury apartments could not be sated, savvy developers enlisted world-renowned architects to make their buildings stand out from the rest. Now, three such buildings featuring highly innovative facades are completing construction, from the Financial District to Greenwich Village to Chelsea.
Forest City Ratner hired none other than Frank Gehry to put his signature on what will be the tallest residential building in Gotham. The unprecedented stainless-steel folds that now drape all but the top few floors of the over-850-foot-tall Beekman Tower have already created a new landmark on Lower Manhattan's skyline beside Cass Gilbert's Woolworth Building and the Brooklyn Bridge. "I designed this building for New York," says Gehry, FAIA. "I'm a deeply rooted contextualist regardless of what anybody says. I stair-stepped the building like a New York skyscraper. It fits in without pandering to, or copying, its neighbors."
To produce the tower's distinctive, wavy skin in a cost-efficient and easily constructible process, Gehry Partners (GP) developed a concept for a flat, unitized curtain wall with a back-ventilated rain-screen cladding attached to its front. The firm solicited technical proposals and cost estimates from three curtain-wall contractors early in design development. Permasteelisa, with whom GP had worked previously on such projects as the Guggenheim Museum Bilbao and the Walt Disney Concert Hall in Los Angeles, was selected to procure and engineer the wall through the construction-documents phase of the project in a highly collaborative effort that also included Gehry Technologies (GT).
Photo: Permasteelisa Group |  |
Computer models of the T-shaped tower were created by scanning physical models, a process that produced point clouds of scalable data. Designers used Rhino software to do preliminary surfacing of the building, but once those forms were refined, the team switched to Digital Project, an offshoot of Catia, Dassault Systèmes' aerospace and automotive design program, which GT developed to be a more user-friendly platform for the architecture and engineering community. "No other platform out there could have made Beekman Tower," says Terry Bell, GP's project partner. "It is the only one that has the ability to analyze surfaces in a sophisticated way that can be tied to parametrics and script writing."
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| Beekman Tower's curving, 16-gauge stainless-steel face sheets are riveted to an aluminum rain screen subframe which were then attached to the flat, unitized curtain-wall panels in the shop. The assembly is hung from the cast-in-place concrete floor slab at aluminum embeds along the slab edge. |
This was especially crucial as the tower's design began to go through several iterations. Since work on the project began in 2003, the shifting economy caused dramatic changes in program, and even threatened to cut the building in half. "That was devastating for a while to contemplate," Gehry recalls.
The switch from condominiums to a building composed entirely of rental units caused significant disruption to the facade because of adjusted floor-to-floor heights and smaller room sizes. "Whenever a unit changes, everything shifts on the surface," explains GT's Dennis Shelden. "The flow of the metal is different."
The digitized physical surface allowed the designers the flexibility to tweak the facade yet still remain within established parameters. For instance, the rain-screen panels can curve out as much as 6 feet; the minimum projection is 6 inches. Throughout the process, Permasteelisa used the revised dimensions and geometries of the 10,300 curtain-wall units to update pricing and automate production.
"We developed a naming convention with Permasteelisa for the different units," says Bell. "All the various component sizes, angles, and extrusion types could be tracked to a particular unit. They were also tied to the manufacturing process with CNC data through to fabrication and installation."
While the facade is complex, the building's concrete structure is straightforward. But because of the surface's waves, each tower floor plate is unique (a rectangular, brick-clad structure forms the building's base). Pouring the concrete slab became complicated at the slab edges, where 4-inch-deep aluminum embeds, to which the curtain-wall units are fit, needed to be precisely located. Three separate surveyors were used to verify the coordinates of the embeds.
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| The folds of the facade become bay windows for the apartments. Photo: © William Paterson |
The 16-gauge stainless-steel face sheets of the rain screen were produced in Permasteelisa's factory in Grand Rapids, Michigan, while the flat curtain-wall units were fabricated in its Miami facility. Despite the complicated geometry of the facade, the shop-fabricated wall assemblies of the unitized system made installation easy and economical.
The design team says there was no cost premium for the curving facade. The tower's southern wall, by contrast, is completely flat. "That was a design choice," says Gehry. "I wanted it to slice. When you see the building in profile from the east and west it looks like someone took a rock and cut it."
One Jackson Square
At the intersection of Greenwich and Eighth Avenues in Manhattan's Greenwich Village, an oddly shaped lot sat empty for nearly a century. The last occupant of the site was a string of row houses that was torn down in the 1920s to make room for a subway tunnel beneath it. For years, building over the tunnel proved too expensive to be worthwhile. But with the escalation of the New York real estate market in the last decade, the investment in construction there finally seemed justified.
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| KPF's One Jackson Square in New York's Greenwich Village features an undulating wall of glass and metal. Photo: © Michael Moran |
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| Apartment interiors have floor-to-ceiling fixed and operable window units. Photo: © Michael Moran |
Kohn Pedersen Fox (KPF) was hired by Hines, the developer, to design a completely as-of-right building while maximizing the zoning volume. The corner portion of the site could rise as high as 11 stories, while the rest was limited to seven. "We treated the zoning volume like a rock in a stream," says William Pedersen, FAIA, design partner at KPF. "We allowed the surface to pour over the volume to modify its character and create something more acceptable architecturally." The designers envisioned a wall of glass since that was the best material they could imagine to unify the strange form in a consistent manner, but they wanted to deal with glass in a way that was unprecedented.
"We didn't want it to look like an office building," says KPF's Trent Tesch, AIA. "The more individuality we could give to each floor, the better." KPF created a series of striations that flowed horizontally through the building. Each striation is different from the one above it and below it in terms of the way it curves and the arrangement of windows it contains.
"The detail that allowed this resolution between the various layers is the key detail of the whole building," says Pedersen. "These constantly reversed positions pulling back and forth create the ability to separate the overlapping layers." Within each of these undulating ribbons, a series of 18-, 36-, and 48-inch-wide custom, floor-to-ceiling fixed and operable windows — all of which are completely flat — animate the facade.
"Because of all its facets, the glass wall becomes a kaleidoscopic playback of everything that surrounds it," says Pedersen. "An ordinary glass wall just reflects its context pretty much as you see it. This wall transforms it."
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| Window dimensions vary, as do the curving ribbons of each floor. Photo: © Michael Moran |
Convincing the New York City Landmarks Preservation Commission, as well as the building's neighbors, that a glass wall was the way to go in the historic district presented challenges, but once approved, the real challenge came in building the structure.
Since construction of the building was scheduled to proceed during the height of New York's building boom, it was nearly impossible to get a large curtain-wall company to take interest in such a relatively small project. Curtain-wall consultant Gilsanz Murray Steficek came up with a concept that would allow the unique wall to be built as a stick system, which meant that much of its assembly would take place on-site. The job of putting it together went to contractors whose experience lay mainly in fabricating storefronts, not luxury apartment buildings.
The metal contractors anchored 18-foot-long horizontal sections, bent according to information provided by 3D computer models, to the floor slabs. As with Beekman Tower, it was critical that the concrete slab edges were formed precisely so that the mullion joints would align and the system would be plumb both vertically and horizontally. In a couple of the units containing double-height spaces, a large beam replaces the slab edge.
Another thing One Jackson Square had in common with Beekman Tower was the constantly changing unit mix. (The finished building contains 32 units, with retail expected on the ground floor). The undulating wall proved perfect for providing the needed flexibility. KPF developed a scheme that had four panel types and one variant. Wherever a partition ended up, a vertical mullion could be added at that point in space. The contractors installed the vertical mullions within the horizontal sections on-site. The framed windows, containing low-iron, reflective glass, were then added.
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| One Jackson Square's glass exterior becomes a constantly changing image of what is surrounding the building. Photo: © Raimund Koch |
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100 Eleventh Avenue
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| The gridded facade of Jean Nouvel's 100 Eleventh Avenue contrasts with Gehry's billowing IA C Building. Photo: © Philippe Ruault |
Just north of One Jackson Square in Chelsea, on a corner lot that sits opposite the billowing IAC Building, Frank Gehry's first building in New York City, Jean Nouvel has created a kaleidoscopic facade with an entirely different character from that of the KPF building.
The De Stijl—like composition of the 250-foot-tall, curving curtain wall is a tour de force of glass and metal. According to Nouvel, "The architecture expresses the exceptional pleasure of being at this strategic point of Manhattan."
The open site is on Manhattan's extreme West Side. Many apartments within the building have unobstructed views of the Hudson River. While Nouvel wanted to capture those views as much as possible, along with the changing light, he was not interested in dematerializing the wall. "We wanted the mullions to look strong and create strong frames," says François Leininger, Ateliers Jean Nouvel's project manager. "You can feel the presence of metal."
Facade consultants Front worked with Nouvel's office to create a curtain wall that featured fixed and operable tilting windows of various sizes and shapes — in essence, a random series of folding planes. To give some regularity to the wall, the team — which included curtain-wall fabricators in China — created megapanels, some as large as 12 feet high by 37 feet wide and containing as many as 20 smaller, individual panels. The megapanel joints are the only areas on the facade that have a continuous vertical mullion. The curving section of the facade features a concentration of smaller panels. Several mock-ups were built both in China and the U.S. to evaluate the wall's aesthetic appearance and performance.
"There is a huge amount of dimensional variety," says Front's Marc Simmons. "But it is not a mathematically generated facade. It really is hand composed from a very architectural idea. It is a game of fragmentation."
Because of the fragmenting lines, the load path from slab to slab is not continuous. Steel forms the facade's structure since the nonlinear load paths and massive panels would have conspired to make an aluminum structure too large to be attractive inside the apartments. All the 3-inch-wide steel elements sit in the same plane, but vary in depth. The steel frame, which is visible from the apartment interiors, is composed of laser-cut steel plates that were welded together, sandblasted, and painted silver. Interiors feature polished concrete ceilings and terrazzo floors.
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| A crane lifts one of the curtain wall's megapanels into place during construction of the facade. Photo: Front Inc. |
"The wall was really designed from the inside out," Simmons explains. "A typical floor features seven megapanels, and each megapanel corresponds to a room. In the largest rooms, you have a 37-foot-wide panorama that eradicates all evidence of traditional curtain-wall construction."
Simmons describes this curtain wall as a hybrid, one that combines characteristics of a window wall where individual panels have no structural dependency on adjacent panels. "The fact is, hybrids are becoming much more common because they can achieve certain architectural intentions that could not be achieved by traditional aluminum unitized curtain walls," he explains. "Those are optimized for fabrication efficiencies and ease of transport. The megapanels on this project are so large and heavy that they can't overlap or have interlocking legs. They are independent of each other."
The exterior layer is silver anodized aluminum to match the silver-painted steel on the interior. While not structural, the aluminum holds the low-E glass panels, which are insulated and laminated. Three different glass coatings were selected to provide a variety of colors on the facade. The glass adheres to a strict STC rating required by noise ordinances for buildings along Manhattan's West Side Highway.
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| The anodized aluminum mullions match the silver-painted steel sections on the inside. Photo: © Philippe Ruault |
The aluminum mullions also provide the waterproofing (which steel is not good at doing). The waterproofing consists of a series of gaskets and sealant. The cruciform joint where four panels come together is an injection-molded accordion gasket. According to Simmons, "It is a common approach to combine the design intelligence of aluminum with the robust, abstract nature of a steel backup."
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| A regular grid of megapanels contains the more random composition of smaller frames. Most floors feature seven megapanels. |
The aluminum caps on the front of the facade vary in depth to create a variety of shadow lines over the building. "There is no visual plane that has any dimensional stability," says Simmons. "It is a very complex but organic assembly."
According to Leininger, the tilting planes and various materials create a patchwork of colors and reflections. "From one angle you catch glimpses of the Gehry building; from another,
the sky and sunset."
For the lower apartments that do not have views out to the river, Nouvel offers a different amenity. A thin wall rises several stories as a buffer between the building and the street. The design calls for a vertical garden within that 15-foot-wide space, where trees will be planted at different heights. "From the same apartment, you may see the top of one tree and the trunk of another," Leininger explains.
Interestingly, while the facades of all three buildings — Beekman Tower, One Jackson Square, and 100 Eleventh Avenue — push the limits of construction with their groundbreaking uses of metal and glass, all prominently feature traditional masonry walls as well.
While the undulating glass wall of One Jackson Square reflects the brick buildings surrounding it, the brick of its own back wall serves practical purposes. Because the building sits above a subway tunnel, it required a robust structure. The masonry wall takes the lateral loads on the building and brings them down into the foundation.
The other two buildings include brick to address their immediate contexts. In Beekman Tower, the first five floors — which will house a primary school, office and retail space, and the residential lobby — are clad in buff-colored brick, and act as a simple pedestal for the sculptural form of the tower above. "For better or worse, it was my decision to make the bottom matter-of-fact so it fit in with the rest of the neighborhood," says Gehry. "There's enough height that the rest of the architecture is pretty damn strong."
For 100 Eleventh Avenue, the view from the east is a much different one than the shimmering glass wall that faces the water. The solid wall on this side of the building takes a more minimal approach — its black brick punctuated by a few randomly arranged windows on each floor. According to Leininger, a key to understanding the building's envelope is recognizing the diversity of its context. "There is the contrast of wide open views to the river from the transparent steel-and-glass facade, and the specific views to Midtown — like paintings on a wall — from the punched windows of the brick facade."
http://continuingeducation.construction.com/article.php?L=5&C=695
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