A window is an opening in an otherwise solid and opaque surface that allows the passage of light and, if not closed or sealed, air and sound. Windows are usually glazed or covered in some other transparent or translucent material. Windows are held in place by frames, which prevent them from collapsing.
Etymology:
The word Window originates from the Old Norse vindauga, from vindr "wind" and auga "eye." "Vindauga" is still used in Icelandic, as well as some Norwegian and Swedish dialects to mean exactly the same thing: window. It is first recorded in the early 13th century, and originally referred to an unglazed hole in a roof. Window replaced the Old English eagþyrl, which literally means "eye-hole," and eagduru, "eye-door". Most Germanic languages however adopted the Latin word fenestra to describe a window with glass, such as Swedish fönster, or German Fenster. Notable exceptions to this, apart from English, are Danish and Norwegian, with the English word window closely resembling the words vindue and vindu respectively. This is probably due to the Scandinavian influence on the English language by means of loanwords during the Viking Age. In English the word fenester was used as a parallel until the mid-1700s and fenestration is still used to describe the arrangement of windows within a facade.
Definition and types of windows:
A window is an opening in a wall that lets light and possibly air into the room and allows occupants to see out. Primitive windows were just holes. Later, they were covered with animal hide, cloth, or wood. Shutters that could be opened and closed came next. Over time, windows were built that both protected the inhabitants from the elements and transmitted light: mullioned glass windows, which joined multiple small pieces of glass with leading, paper windows, flattened pieces of translucent animal horn, and plates of thinly sliced marble. Mullioned glass windows were the windows of choice among European well-to-do, whereas paper windows were economical and widely used in ancient China and Japan. In England, glass became common in the windows of ordinary homes only in the early 17th century whereas windows made up of panes of flattened animal horn[citation needed] were used as early as the 14th century in Northern Britain. Modern-style floor-to-ceiling windows became possible only after the industrial glass making process was perfected. Evidence of glass window panes in Italy dates back nearly 3000 years.
Modern windows are customarily large rectangles or squares with glass surfaces. Churches traditionally have stained glass windows.
Modern domestic windows come in many styles. The choice of design varies throughout the world, and is largely dictated by the prevailing weather conditions. Coastal climates tend to have smaller outward-opening windows due to the stronger winds experienced - e.g. England. Continental climates tend to have larger windows, many of which open inwards - e.g. France and Germany. Styles available include:Double-hung sash window.
The traditional style of window in the USA, and many other places that were formerly colonized by the UK, with two parts (sashes) that overlap slightly and slide up and down inside the frame. The two parts are not necessarily the same size. Nowadays, most new double-hung sash windows use spring balances to support the sashes, but traditionally, counterweights held in boxes either side of the window were used. These were and are attached to the sashes using pulleys of either braided cord or, later, purpose-made chain. Double-hung sash windows were traditionally often fitted with shutters. Sash windows may be fitted with simplex hinges which allow the window to be locked into hinges on one side, while the rope on the other side is detached, allowing the window to be opened for escape or cleaning.
Single-hung sash window:
One sash is movable (usually the bottom one) and the other fixed. This is the earlier form of sliding sash window, and is obviously also cheaper.
Horizontal sliding sash window:
Has two or more sashes that overlap slightly but slide horizontally within the frame. In the UK, these are sometimes called Yorkshire sash windows, presumably because of their traditional use in that county.
Casement window:
A window with a hinged sash that swings in or out like a door comprising either a side-hung, top-hung, or occasionally bottom-hung sash or a combination of these types, sometimes with fixed panels on one or more sides of the sash. In the USA these are usually opened using a crank, but in Europe they tend to use projection friction stays and espagnolette locking. Formerly, plain hinges were used with a casement stay. Handing applies to casement windows to determine direction of swing.
Jalousie window
Also known as a louvred window, this window is comprised of many slats of glass that open and close like a Venetian blind, usually using a crank or a lever. The hinges may be at the top or middle of the short end of the slats of glass. They are used extensively in tropical and subtropical architecture, for instance, throughout the Philippines and in Queensland, Australia. A Jalousie door is a door with a Jalousie window.
Technical terms:
Etymologically speaking, any window can be called a "light". However, within the window industry, particularly in insulated glass production, the term "lite" (so-spelled to keep the meaning differentiated from actual sunlight) is used to mean a single glass pane, several of which may be used to construct the final window product. For example, a sash unit, consisting of at least one sliding glass component, is typically composed of two lites, while a fixed window is composed of one lite. The terms "single-light", "double-light" etc refer to the number of these glass panes in a window.
The lights in a window sash are divided horizontally and vertically by narrow strips of wood or metal called muntins. More substantial load bearing or structural vertical dividers are called mullions, with the corresponding horizontal dividers referred to as transoms.
In the USA, the term replacement window means a framed window designed to slip inside the original window frame from the inside after the old sashes are removed. In Europe, however, it usually means a complete window including a replacement outer frame.
The USA term new construction window means a window with a nailing fin designed to be inserted into a rough opening from the outside before applying siding and inside trim. A nailing fin is a projection on the outer frame of the window in the same plane as the glazing, which overlaps the prepared opening, and can thus be 'nailed' into place).
In the UK and Europe, windows in new-build houses are usually fixed with long screws into expanding plastic plugs in the brickwork. A gap of up to 13mm is left around all four sides, and filled with expanding polyurethane foam. This makes the window fixing weatherproof but allows for expansion due to heat.
Insulated window frames:
Windows can be a significant source of heat transfer[2]. Different kinds of glazing and window frames can reduce thermal losses and gains.
Frames and sashes are traditionally made of wood, but metal, vinyl or PVC, and composites are also common. The cost and availability of may vary from country to country. Solid metal frames and sashes are poor insulators because metals conduct heat quickly. Vinyl frames are popular in Europe because they conduct heat poorly. Wood is also a good insulator. Composite frames may combine materials to obtain aesthetics of one material with the functional benefits of another. Modern metal window parts typically consist of two surfaces separated by insulating spacer material.
Many windows have movable window coverings such as blinds or curtains to keep out light, provide additional insulation, or ensure privacy.
Air infiltration and hence convective heat losses can be reduce by good window seals and attention to construction. Evacuated or argon-filled Insulated glazing units are also dependent on meticulous frame construction to prevent entry of air and loss of efficiency.
Window construction:
Modern windows are usually glazed with one large sheet of glass per sash, while windows in the past were glazed with multiple panes separated by "glazing bars", or "muntins", due to the unavailability of large sheets of glass. Today, glazing bars tend to be decorative, separating windows into small panes of glass even though larger panes of glass are available, generally in a pattern dictated by the architectural style at use. Glazing bars are typically wooden, but occasionally lead glazing bars soldered in place are used for more intricate glazing patterns.
A beam over the top of a window is known as the lintel or transom.