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

The direct lineage of Enclos 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.

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.

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.

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.

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.

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.

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.

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: