A Tall Tale: A Brief History of Curtainwall and The Tower

The direct lineage of Enclos Corp dates to the very advent of curtainwall as a building form in the mid-20th century. As one of the first companies active in this new marketplace, Enclos has played a leading role in developing this technology through the years into the refined, high performance curtainwall systems of today.

The technological roots of today’s curtainwall systems reach all the way back to the great iron and glass greenhouse structures constructed in 19th century England and Europe, most famously the Crystal Palace designed and built by engineer/architect Joseph Paxton in 1851. These structures were made possible by the development of wrought and cast iron structural members and a burgeoning glass industry capable of supplying large quantities of relatively inexpensive flat glass. This combination represented a paradigm shift from the predominant masonry-based building technology that had dominated the built environment for centuries (and continued to do so well into the 20th century). Paxton and his contemporaries were able to construct structural load-bearing frames from the steel members. The glass was simply “draped” across the frame as a nonstructural cladding material.


Crystal Palace, 1850, London, by Joseph Paxton

At the same time increasing urban density and escalating land values were creating pressure to build upwards, pushing the limits of the masonry building practices of the time. A Chicago engineer named William Jenney devised a method of steel framing towards the end of the 19th century that gave birth to the technology of high-rise buildings. Exterior walls were no longer load bearing and the ubiquitous practice of masonry wall construction, because of the weight of the masonry material, became an unnecessary liability with the steel-framed structural systems. Change is not a direct consequence of innovation however, and masonry remained the predominant wall material for many years to come. Still, the elements were in place for a new technique of building construction, which the Chicago architects were actively exploring by the turn of the century.


The Gage Building, 1898, by Holabird and Roche and Louis Sullivan

Led by the stunning work of Walter Gropius, Mies van der Rohe, Skidmore, Owings & Merrill LLP and others, it took post-war modernism, a new revolution in glass production technology, and an increasing supply of low cost aluminum to finally break the old masonry paradigm and bring forth the new era of high-rise building: the skyscraper.


Carson Pirie Scott Store, 1899-1904, by Louis Sullivan

Glass use exploded in the mid-20th century, beginning its march to the ubiquitous building commodity it is today. The demand was fueled by the Modernist style, but the explosion was ignited by the invention of the float process for manufacture of flat glass at mid-century, replacing the drawn-glass production method of the time. The float process was economically viable by the 1960s and remains the predominant means for the manufacture of architectural glass today. An inexpensive source of quality flat glass was a major factor in the innovations that occurred in building technology at mid-century.

Designers seeking solutions to replace masonry as cladding material for the new high-rise architecture eventually discovered a solution in a material and process relatively new to the construction industry: extruded aluminum. By mid-century, aluminum supply was abundant and economical. The extrusion process provided an efficient manufacturing process to convert the aluminum into linear sections of complex geometry, perfect for framing flat panel materials such as glass.


Reliance Building, 1894, by DH Burnham and Company

Using these newly available materials, building designers embraced the examples produced by the small handful of visionary designers that initiated the Modernist Movement in the first half of the century. Commercial building developers in the booming post-war economies of American and Western Europe recognized in these new low-cost cladding strategies a means to maximize leasable square footage in a given footprint. These new cladding systems came to be referred to as “curtainwall” because they were non load-bearing systems that were simply hung from the structure like a curtain. Thus, in the 1950s the modern curtainwall industry was born amidst a profusion of high-rise curtainwalled structures.


Bauhaus Building, 1926, Dessau, by Walter Gropius

One of the very early entrants into this new industry was a company called Cupples Products. Started in 1946 as a manufacturer of residential window products, the company rapidly progressed into the design development, engineering, fabrication, assembly and field installation of custom curtainwall systems, providing solutions to architects and builders eager for new facade technology. A later but equally influential entrant to the emergent curtainwall industry operated over the decades under the names of Harmon Contract, Harmon Ltd, and Enclos Corp, completing many landmark projects.


The Leverhouse, 1952, New York City, widely recognized as the first curtainwall building to be constructed in the United States (photo by David Shankbone)

Both Cupples and Enclos followed growth paths paralleling the boom in urban high-rise construction, actually enabling the boom as providers of continuously evolving exterior facade technology. By the end of the 20th century the two companies had effectively merged, operating as sister companies under the same umbrella with Enclos focusing on the domestic US marketplace and Cupples on International markets.


Seagram Building, 1954, New York City, by Mies van der Rohe

Starting with Cupples’ involvement with I.M. Pei and the Webb & Knapp Executive Offices completed in 1954, the companies have worked with leading architects through the years in providing custom curtainwall systems on many significant landmark domestic and international buildings.

A select few follow:

John Hancock Tower, Chicago 1969; architect – Skidmore, Owings & Merrill LLP 100-stories, 1127 feet. This building is one of the most famous of the expressionist style, with its dramatically exposed diagonal bracing.
Aon Center (formerly Standard Oil Building), Chicago 1972; architect – Edward Durell Stone; Perkins + Will At 83-stories and 1,136 feet, this is the 3rd tallest building in Chicago. When completed, it was the tallest building in Chicago and the 4th tallest in the world.
Sears Tower, Chicago 1973; architect – Skidmore, Owings & Merrill LLP At 108-stories and 1,730 feet, the Sears Tower has been the tallest building in North America since it was completed in 1973, surpassing the World Trade Center, which had only recently surpassed the Empire State Building.
World Trade Center Towers, New York 1973; architect – Minoru Yamasaki 110-stories, 1727 feet. The “Twin Towers” were destroyed in the September 11, 2001 terrorist attack. Six new skyscrapers and a memorial have since been built on the site.
JP Morgan Chase Tower (formerly Texas Commerce Tower), Houston 1982; architect – Pei Cobb Freed & Partners Architects LLP 75-stories, 1,002 feet. This skyscraper is the tallest building in Texas, the tallest 5-sided building in the world, and one of the world’s tallest structures.
Transco Tower (or Williams Tower), Houston 1984; architect – Philip Johnson; Pritzker Prize Laureate At 64-stories and 901 feet, this is the tallest tower not located in an urban center.
Hong Kong and Shanghai Bank Headquarters, Hong Kong 1985; architect – Foster + Partners 47-stories. The exposed structure and innovative design made this project controversial, as well as the most expensive building of its time. Cupples provided one of the largest facade programs of all time, including castings, metal panels and glass.
Petronas Towers, Kuala Lumpur 1992; architect – Pelli Clarke Pelli Architects At 88-stories and 1,483 feet, the Petronas Towers was the tallest building in the world from 1998 (surpassing the Sears Tower, also completed by Enclos Corp) to 2004, when surpassed by Taipei 101. Petronas is still the tallest twin towers in the world.
Shinjuku I-Land Tower, Tokyo Japan 1995; architect – Nikken Sekkei 44-stories, 620 feet. The design has an unusual edge profile which significantly increased the complexity of the curtainwall system.
Republic Plaza, Singapore 1995; architect – Kisho Kurokawa Architect and Associates At 66-stories and 920 feet, Republic Plaza is one of the three tallest buildings in Singapore.
Puerta de Europa, Madrid 1996; architect – Philip Johnson and John Burgee Two 26-story towers with 15-degree inclinations.
Bandaijima Building, Niigata 2003; architect – Kajima Design. This 31-story, 460 foot tower is the tallest building in the region. While only 43 miles from the epicenter of the 2004 Niigata Chuetsu earthquake, it suffered no damage.
Torre Mayor, Mexico City 2003; architect – Adamson Associates Architects / Zeidler Partnership Architects At 55-stories and 740 feet, Torre Mayor is Mexico’s tallest building, and was Latin America’s tallest from 2003 to 2008. The project included extensive seismic analysis on the curtainwall system.