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The curtain wall, one of architecture's most provocative metaphors, is
surprisingly difficult to pin down with a precise definition. Because it can
be examined from multiple perspectives—(1) in terms of functional
relationships, (2) as an aesthetic object, or (3) as a mass-produced system
available within the construction marketplace—some ambiguity is inevitable.
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Curtain wall mullion being fastened to structural slab |
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Curtain wall fastened to structure in Gehry's Disney Concert Hall |
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Willis Polk's Halladie Building (1917): curtain wall or large
window? |
In the first case, the curtain wall is defined in terms of its functional
relationship to the building's structure. It then refers to the cladding, or
enclosure, of a building as something both separate from and attached to the
building's skeletal framework. Where loadbearing walls provide both
structure and enclosure, there can be no curtain wall. But difficulties
emerge within this first definition when the question of "infill" is
considered: are conventional windows (or other infill material), when fixed
inside the boundaries of a structural frame, considered to represent curtain
wall construction? Such construction is certainly "attached" to the
structural frame, but not exactly "hanging" from it. When is a window just a
window within a frame, and when does it transform into a curtain wall? The
answer may have more to do with one's aesthetic bias than with the actual
functional relationship between cladding and structure.
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Sullivan's Bayard Building with thick masonry curtain wall |
From a functional perspective, curtain walls necessarily appeared precisely
at the same time as did skeletal frameworks—towards the end of the 19th
century. Yet the first such walls were often strikingly similar to the thick
masonry walls they might have been expected to supersede. Though no longer
loadbearing structure, relatively thick masonry curtain walls continued to
be used in steel and concrete-framed buildings for other reasons: first,
thinner masonry walls—before the development of internal cavities to block
the migration of moisture through the wall—tended to have problems with
water penetration. Second, lighter facades consisting of metal or glass
panels were often considered aesthetically unsuitable for serious works of
architecture, owing to the legacy and tradition which linked monumental
architecture to masonry construction. Third, the use of more modern cladding
alternatives required breakthroughs in environmental control
technologies—air conditioning and insulation being the most important—before
they could be deployed over large surface areas enclosing habitable spaces.
Finally, building code officials, increasingly sensitive to the real danger
of urban conflagrations, prevented the use of new, lightweight materials in
exterior walls—even after other technical and environmental issues had been
addressed—if they were unable to match the proven fire-resistance of
masonry.
Although defined initially in terms of its functional relationship to
structure, towards the middle of the 20th century the curtain wall began to
be alternatively defined by its function as an environmental filter—as a
membrane mediating between desired interior conditions and variable exterior
circumstances. Sun screens (brise-soleil), double glazing, and
pressure-equalized rain screens were among the functional responses to this
concern, culminating in the late 20th-century's technologically
sophisticated "bioclimatic" designs. In these "green" buildings, an array of
computer-controlled and user-controlled devices may be embedded within the
curtain wall to encourage the use of fresh air and natural daylighting,
while at the same time aiming to improve user comfort, reduce energy
consumption, and promote a "sustainable" lifestyle.
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Corbusier: Cité de Refuge with brise-soleil added to facade |
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Pressure-equalized curtain wall mullion |
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Foster's Commerzbank: "Green" double-skin curtain wall |
Curtain walls can also be defined as the embodiment of an aesthetic
intention—the second of the three perspectives mentioned above. Numerous
such curtain wall themes can be identified in 20th-century architecture.
They coalesce, in general, around the revolutionary "new" materials of metal
and glass: metal (as industrialized, mass-produced, streamlined panel);
glass (as transparent or reflective surface, crystalline solid, or harbinger
of an enlightened culture); or metal and glass combined (as woven "fabric,"
or abstract grid). Still, other more traditional materials and systems,
including stucco, concrete, brick and stone veneer have also played a role
in validating the curtain wall within various aesthetic domains, and not
merely as the byproduct of functional considerations. The ideal of an
all-glass skin has been perhaps the most persistent curtain wall theme
throughout the 20th century. Starting with metal window systems containing
relatively small glass panes, and moving towards larger glass sizes with
smaller mullion profiles, the most technically-advanced glass walls of the
late 20th century have managed to eliminate mullions entirely, whether by
using the glass itself as a structural material, relying on structural
sealant joints, or pinning the glass to elegantly-detailed lightweight steel
sub-structures.
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Harrison and Abramovitz: Socony Mobil Building with steel panels |
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Stubbins: Citicorp Center with metal and glass curtain wall |
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Richard Meier: Getty Center's metal panel system |
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Pei: Hancock Building as reflective, crystalline surface |
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Mies: Seagrams Building with metal and glass "woven" grid" |
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Pelli: Pacific Design Center as sculptural reflective surface |
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Foster: Willis Faber Dumas building literally hangs curtain of
transparent/reflective glass |
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Roche & Dinkeloo: UN Hotel uses curtain wall to reinforce abstract
gridded geometry |
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Nouvel: Foundation Cartier explores issues of transparency |
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Bruno Taut: Glass pavilion (1914) as harbinger of enlightened
culture |
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Foster: Reichstag dome as modern version of same theme |
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Grimshaw: Waterloo Terminal uses "structural" glass without mullions |
Ironically, the initial aesthetic formulation of the modern metal and glass
curtain wall preceded the invention of multistory skeletal frameworks.
Greenhouses were being built in Europe, even in the mid-17th century, with
large areas of glass divided by wooden, and later iron, mullions. By the
mid-19th century, skins of metal and glass were commonly used for the roofs
of markets, gallerias, and train stations. London's Crystal Palace of 1851
was extremely influential, not only in validating the architectural use of
iron and glass, but in foreshadowing its rationalization as an
industrialized system.
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Paxton's Crystal Palace foreshadows industrial curtain walls |
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Gropius: Bauhaus early steel and glass curtain wall |
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SOM's Lever House: early 1950s curtain wall (Ferriss rendering) |
It is as a system—the third perspective mentioned above—that the curtain
wall became widely available within the building construction marketplace.
Early 20th-century curtain walls tended to be unique and custom-made,
fabricated individually from the cast iron, rolled steel and plate glass
that were just beginning to appear as industrialized commodities. But by the
mid-1930s, the emerging sheet metal technologies (and aesthetics) associated
with the mass-production of airplanes and automobiles began to be seriously
adapted to building construction, especially the development of metal
curtain wall panels. Starting at the end of the Second World War, the
20th-century's ubiquitous metal and glass curtain wall systems—repetitive
grids of extruded aluminum mullions and horizontal rails, fastened to a
building's structural skeleton, and supporting panels of glass or
metal—increasingly began to appear on commercial and institutional
buildings. The newly-invented float process made large areas of glass even
more feasible beginning in the 1950s.
Other panelized curtain wall systems also appeared as cladding options:
these included composite metal panels containing lightweight cores of
honeycombed material or foamed plastic insulation sandwiched between two
layers of thin sheet metal (aluminum or steel); precast concrete panels,
custom-designed for each job, but still manufactured within a
rationalized, systematic production setting; and thin stone veneer panels
factory-cut to a thickness as little as one inch, then attached to the
building's structure using proprietary metal clips and anchors. Even
traditional brick and stucco became integrated into manufactured curtain
wall systems: brick as part of layered cavity wall systems; stucco, most
commonly in the form of E.I.F.S. (exterior insulation and finish systems),
consisting of thin polymer-based plaster lamina applied with fiberglass
reinforcing mesh to a surface of rigid foam insulation.
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Metal composite panel system (Formawall) |
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Precast concrete curtain wall |
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Thin stone veneer (Stirling: Performing Arts Center showing damage
to veneer) |
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Brick/CMU cavity wall (from R. Brand) |
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Plaster/stucco (Gehry: Team Disney) |
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EIFS (Dryvit system) |
Further reading:
The history of curtain walls in 20th-century architecture can be pieced
together from readings in architectural histories and from monographs
describing the work of individual architects or designers. For the
development of early 20th-century curtain walls in Chicago, see: Condit,
Carl, The Chicago School of Architecture; a History of Commercial and
Public Building in the Chicago Area, 1875-1925, Chicago: University of
Chicago Press, 1964; a discussion of the rival cast-iron tradition can be
found in: Gayle, Margot and Gayle, Carol, Cast-Iron Architecture in
America: The Significance of James Bogardus, New York: Norton and Co.,
1998. Individual monographs are too numerous to list; of the many
20th-century architects or designers associated with the development of
curtain wall technology, or its aesthetic refinement, a partial list would
include: Nicholas Grimshaw, Norman Foster, Walter Gropius, Le Corbusier,
Richard Meier, Jean Nouvel, I.M. Pei, Cesar Pelli, Jean Prouvé, Peter Rice,
Kevin Roche, Mies van der Rohe, Eero Saarinen, Ken Yeang, and the firm of
Skidmore Owings and Merrill.
For a general text examining modern curtain wall systems, see: Sands,
Herman, Wall Systems : Analysis by Detail, New York: McGraw-Hill,
1986. An overview of curtain wall systems can be found in: Allen, Edward,
Fundamentals of Building Construction, 3rd edition, New York: Wiley,
1999; discussion and details of early "modernist" 20th-century curtain walls
can be found in: Ford, Edward, The Details of Modern Architecture,
Cambridge: M.I.T. Press, 1990.
For examples of state-of-the-art "glass walls," see: Bramante, Gabriele,
Willis Faber & Dumas Building: Foster Associates, London: Phaidon
Press, 1993; and Rice, Peter and Dutton, Hugh, Structural Glass,
London: E & FN Spon, 1995.
For innovations in the production and design of metal curtain wall
panels, see: Huber, Benedikt and Steinegger, editors, Jean Prouvé :
Prefabrication, Structures and Elements, London: Pall Mall Press, 1971;
for a more recent oeuvre incorporating metal curtain wall panels, see, for
example: Flagge, Ingeborg and Hamm, Oliver, editors, Richard Meier in
Europe, Berlin: Ernst & Sohn, 1997.
For examples of "green" curtain wall designs, see: Yeang, Ken,
Bioclimatic Skyscrapers, London: Artemis, 1994; and Davies, Colin and
Ian Lambot, Commerzbank Frankfurt: Prototype for an Ecological High-Rise,
Boston : Watermark, 1997.
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