Windows are one of the most expressive and complex features of a building. They have been called “the eyes of a building,” an analogy that reveals how important they are to the character of a building. Windows also perform many functions—thermal envelope, light transmitting, sound control and ventilation. While most building parts are fixed, the window was an operating feature in order to provide natural ventilation, which made it even more complex. An element with this much importance in design and function is well represented in the documents in the Building Technology Heritage Library (BTHL).
The ubiquitous wood, double-hung window was a typical feature of residential and commercial buildings through most of America’s history. Variations in opening size, sash patterns, and shape were all part of the design evolution while the material of wood stayed the same. Most millwork catalogs of the 19th and early 20th centuries featured wood windows, including more complex shapes such as arched tops or bow windows. In the 20th century, national companies that just specialized in windows replace millwork companies in the marketplace.
In the 20th century there was a lot of innovation in window design in materials as steel and later aluminum windows started to complete with wood. The use of casement windows instead of double-hung windows grew in popularity and were often associated with various architectural styles. Steel casement windows were frequently used in period architectural styles as well as art deco and modernists designs. The development of insulating glass and glass block were two innovations that gained popularity in the 1930s but really took off after World War II.
In addition to windows for the typical American home, there are other special glass types that can be researched. Art glass is generally associated with religious structures but was also quite common in residential use in the late 19th and early 20th centuries. There were also regional window types such as jalousie windows, which graced many a porch in the southern climates of the U.S. In addition to the windows themselves, there are numerous catalogs for window accessories such as drapes, curtains, and blinds.
The APT BTHL documents largely end in 1963, before the first energy crisis of the 1970s and the boom in the replacement window industry. The plethora of window documents in the BTHL reveals a common story, a constant evolution of new materials and designs that enrich the built environment of America.