The window – sign of human life, wink to the passerby, eye of the building allowing one to gaze at the outside world without being seen, welcomer of the daylight and the sun’s ray highlighting surfaces and objects, source of fresh air and sometimes place of exchange of words and smells … but also a break in the wall’s structural continuity, and thus place of vulnerability, fragility, thermal sensitivity, leakage. A basic element in architecture, the window happily takes its place in the introduction to this book. Eye, mouth, nose and ear concurrently it is not only a determining feature in the building’s appearance, but also the intermediary which allows the occupants of a building to see, hear and feel the place of which they are part.
The forms and dimensions of windows have their history. In the primitive hut, one minimal opening served as entrance, view, towards the outside world, source of light and of ventilation. One or two more modest openings were sometimes added. Much later came the glazed window which offers the user the choice between opening and closing it without having to be plunged into darkness. Hitherto the form of windows has been to a certain extent dependent on building techniques for controlling interior lighting and temperature. The lighting efficiency of a window is several times greater when it is near the ceiling than when it is near the ground. Thus the most economical window would be positioned near the ceiling, if it did not also have to take into account view and spatial articulation.
The window therefore encompasses three design functions: that of light, that of view and that of articulation between interior and exterior. Religious and introverted buildings are mainly designed for light. Since the Renaissance several architects have exploited the potential of isolating the design for light from that for view by providing openings or oculi for lighting above the windows which provide the view. The most common traditional window inserted into the masonry wall is still the ‘vertical window’, which combines the three design functions in a single architectural element with a minimal lintel. This was the archetypal window up until the twentieth century.
Thousands of years of traditional practice have now been challenged by new building methods: steel and reinforced concrete have introduced frame construction, which has transformed the bearing wall into a nonbearing membrane. Artificial lighting has done away with the limitations of natural lighting. The vertical window has lost its relationship with the economy of construction and thus been reduced to just one among a number of possibilities. Architecture is no longer guided by the imperatives of limited techniques of construction. Indeed free façades, glazed bays, vertical slots, picture windows, corner windows, glazed verandas, curtain walls and other devices offer many new solutions for modelling space and light.