windows
A window is an opening in the wall of a building for the admission of light and air. At earlier times windows were made of wood, but now they are made of various metals as a result of the progress of the building Industry. The traditional types of windows are double-hung and casement. The double-hung windows are economical, easy to operate and excellent for use in wood-framed houses, they are also easily screened. The casement is a window that opens on hinges. The casement sash provides a full opening, but it warps when it is made of wood. Therefore it is usually made of metals which do not warp if they are well treated. Steel sashes and aluminum alloy sashes are widely used now. Casement sashes are more easily made watertight, but they require inside screening. Window screens are made of copper, aluminum, stainless steel, plastics and galvanized steel. During winter they can be replaced by storm sashes. A cornice is usually placed above the opening to protect it from rain water. Metal window frames are constructed of stainless or ordinary steel or of aluminum and bronze. The window has become larger-often wall to wall and floor to ceiling and often when the building is air-conditioned it has no opening sash members. When large areas of fixed glass are installed the thickness of glass must correspond to its size. Various types Of doubly glazing with an air space between them help to reduce heat losses. Shop windows must be of a sufficient thickness per square foot of exposed area to withstand wind pressures. Vertical Supporting members called mullions, which transfer the wind forces to the structural frame, also vary in thickness and depth according to the glass area which they stiffen. The glass itself may also be designed to perform a specific function such as "Thermopane" (two panes of glass with a hermetically sealed dry air space between) which is used to restrict the heat loss through a window. "Heat absorbent" green glass is used to restrict the passage of heat.
