3 Windows The window is an opening in a wall or side of a building admitting light and often air to the interior. Early windows were developed before the introduction of glass, so initially windows were left open to the external atmosphere, or filled by some form of closure to minimize the heat loss at night. The more sophisticated buildings would have had thin slabs of marble, mica or oiled paper for this purpose. In mediaeval times wooden shutters were installed on the interior, and these were left open or closed to regulate the light and air. With the introduction of glass, used first in small panes in Roman architecture, the window as we know it today had its beginnings. The concept of small panes of glass, divided by bronze or later lead divisions, as used in early buildings dies hard and window manufacturers still offer these as alternatives to fully glazed windows in new domestic work, however inappropriate they may appear. Windows can broadly be divided into two main types, fir...