Prefabrication experiments - 69 - Hope's Windogrid

The curtain wall is conceivably the most important revolution in modern building culture. Originating in the nineteenth century and honed throughout the twentieth century, this revolution introduced the glass building but more importantly supported the disconnection of the building’s envelope from the building’s structural system. The traditional envelope composed of a massive enclosure supported by each floor was substituted by vertical and horizontal lightweight structural profiles hung from the building’s edge. This grid of structural members could be fixed intermittently to a building’s floor edges and sealed with glazed, insulated or decorative panels. This separation of structure and skin released the façade from classic structural rhythms.

Lightweight materials transformed building in Europe and in North America and were consistent with new production capabilities and contributed to improving multilevel buildings, which commanded lighter materials in order to achieve greater vertical spans. Robert Davidson discussed the curtain wall and the separation of structure and skin in a May 1947 article from "architectural Forum". Davidson illustrated the flexible assembly of vertical supports on the edge of slabs as the main constituent of this nimble building strategy. The flexibility allowed for the building’s «structure and skin» to obey different orders. The light glazed walls also decreased traditional massive wall loads. Many different companies developed curtain walls in steel and in wood but most used aluminum sections converging the material’s lightness, its precise production potential and postwar economic downturn for the aluminum industry.

Post-war school building systems were especially conducive for curtain walls as new pedagogy demanded diversity in planning and adaptability while governments demanded systems that optimized prefabrication, industrialisation and transfer of military technologies to civilian use. Although it is impossible to choose one curtain wall system to portray an industry with many variants, Hope's Windogrid did combine the three main constituents that characterise both the forbearers of the modern curtain wall and present day technology: floor edge anchors, vertical and horizontal mullions, and separate pressure caps. Henry Hope and Sons ltd proposed a system for continuous fenestration, which separated steel mullion bars from an extruded aluminum cap section, which held glazed panels in place. The steel bars were fixed to the edge of slab condition while the aluminum grid was set apart from the structure, creating a continuous glazed enclosure.

Windogrid Detail