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A window is a transparent or translucent opening in a wall, door or vehicle 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 like float glass. Windows are held in place by frames. Many glazed windows may be opened, to allow ventilation, or closed, to exclude inclement weather.
The word window originates from the Old Norse 'vindauga', from 'vindr – wind' and 'auga – eye', i.e. "wind eye". In Norwegian Nynorsk and Icelandic the Old Norse form has survived to this day (in Icelandic only as a less used synonym to gluggi), in Swedish the word vindöga remains as a term for a hole through the roof of a hut, and in the Danish language 'vindue' and Norwegian Bokmål 'vindu', the direct link to 'eye' is lost, just like for 'window'. The Danish (but not the Bokmål) word is pronounced fairly similarly to window.
Window 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'. Many Germanic languages however adopted the Latin word 'fenestra' to describe a window with glass, such as standard Swedish 'fönster', or German 'Fenster'. The use of window in English 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-18th century and fenestration is still used to describe the arrangement of windows within a façade. Also, words such as "defenestration" are in use, meaning to throw something out of a window.
From Webster's 1828 Dictionary: Window, n. [G. The vulgar pronunciation is windor, as if from the Welsh gwyntdor, wind-door.]
The earliest windows were just holes in a wall. Later, windows 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. In the Far East, paper was used to fill windows.
The Romans were the first known to use glass for windows. In Alexandria ca. 100 AD, cast glass windows, albeit with poor optical properties, began to appear. Mullioned glass windows were the windows of choice among European well-to-do, whereas paper windows were economical and widely used in ancient China, Korea 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 were used as early as the 14th century.
Modern-style floor-to-ceiling windows became possible only after the industrial glass making process was perfected. Modern windows are usually filled with glass, although a few are transparent plastic.
A window that cannot be opened, whose function is limited to allowing light to enter (Unlike an unfixed window, which can open and close). Clerestory windows are often fixed. Transom windows may be fixed or operable. This type of window is used in situations where light or vision alone is needed as no ventilation is possible windows without the use of trickle vents or overglass vents.
Single-hung sash 
One sash is movable (usually the bottom one) and the other fixed. This is the earlier form of sliding sash window, and is also cheaper.
Double-hung sash 
A sash window is the traditional style of window in the United Kingdom, 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. Currently most new double-hung sash windows use spring balances to support the sashes, but traditionally, counterweights held in boxes on 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 for cleaning.
Horizontal sliding sash 
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.
A window with a hinged sash that swings in or out like a door comprising either a side-hung, top-hung (also called "awning window"; see below), 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 parts of 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; a casement window may be left-handed, right-handed, or double. The casement window is the dominant type now found in the UK and parts of Europe.
A hopper window is a bottom-pivoting casement window that opens by tilting vertically, typically to the inside. (Mostly used for schools)
Tilt and slide 
A window (more usually a door-sized window) where the sash tilts inwards at the top and then slides horizontally behind the fixed pane.
Tilt and turn 
A window which can either tilt inwards at the top, or can open inwards hinged at the side. This is by far the most common type of window in Germany, its country of origin. It is also widespread in many other European countries.
A window above a door; in an exterior door the transom window is often fixed, in an interior door it can open either by hinges at top or bottom, or rotate on hinges. It provided ventilation before forced air heating and cooling. A fan-shaped transom is known as a fanlight, especially in the British Isles.
Jalousie Window 
Also known as a louvered window, the jalousie window consists of parallel slats of glass or acrylic that open and close like a Venetian blind, usually using a crank or a lever. They are used extensively in tropical architecture. A jalousie door is a door with a jalousie window.
A flat or slope window used for daylighting, built into a roof structure that is out of reach.
A sloped window used for daylighting, built into a roof structure. It is one of the few windows that could be used as an exit. Larger roof windows meet building codes for emergency evacuation.
Roof lantern 
A multi-panel window, with at least three panels set at different angles to create a protrusion from the wall line.
A form of bay window most often seen in Tudor-style houses and monasteries which projects from the wall and does not extend to the ground. Originally a form of porch, they are often supported by brackets or corbels.
Thermal, or Diocletian, windows are large semicircular windows (or niches) which are usually divided into three lights (window compartments) by two mullions. The central compartment is often wider than the two side lights on either side of it.
A very large fixed window in a wall, typically without glazing bars or glazed with only perfunctory glazing bars near the edge of the window. Picture windows are intended to provide an unimpeded view, as if framing a picture.
A window glazed with small panes of glass separated by wooden or lead "glazing bars", or "muntins", arranged in a decorative "glazing pattern" often dictated by the architectural style at use. Due to the historic unavailability of large panes of glass, the multi-lit (or "lattice window") was the prevailing style of window until the beginning of the 20th century, and remains used today in traditional architecture.
Emergency exit/egress 
A window big enough and low enough so that occupants can escape through the opening in an emergency, such as a fire. In the United States, exact specifications for emergency windows in bedrooms are given in many building codes. Vehicles, such as buses and aircraft, frequently have emergency exit windows as well.
Stained glass 
A window composed of pieces of colored glass, transparent, translucent or opaque, frequently portraying persons or scenes. Typically the glass in these windows is separated by lead glazing bars. Stained glass windows were popular in Victorian houses and some Wrightian houses, and are especially common in churches.
A French window (when hinged French door) is a large door-sized lattice light, typically set in pairs or multiples thereof. Known as porte-fenêtre in France and portafinestra in Italy, they often overlook a terrace.
EN 12519 is the European norm which describes the terms which are officially being used within EU Member States. Their main terms are also given below:
- Light is the area between the outer parts of a window (transom, sill and jambs), usually filled with a glass pane. Multiple panes are divided by mullions when load-bearing, muntins when not.
- Lattice light is a compound window pane madeup of small pieces of glass held together in a lattice.
- Fixed window is a unit of one non-moving lite. The terms "single-light", "double-light" etc. refer to the number of these glass panes in a window.
- Sash unit is a window consisting of at least one sliding glass component, typically composed of two lites (known as a "double-light").
- Replacement window in the United States means a framed window designed to slip inside the original window frame from the inside after the old sashes are removed. In Europe it usually means a complete window including a replacement outer frame.
- New construction window in the US, the term 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 mainland 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.
- window-sill is the bottom piece in a window frame. Window sills slant outward to drain water away from the inside of the building.
- Secondary Glazing is an additional frame applied to the inside of an existing frame, usually used on protected or listed buildings to achieve higher levels of thermal and sound insulation without compromising the look of the building
- Decorative millwork is the moulding, cornices and lintels often decorating the surrounding edges of the window.
The United States NFRC Window Label lists the following terms:
- Thermal transmittance (U-factor), best values are around U-0.15 (equal to 0.8 W/m2/K)
- Solar heat gain coefficient (SHGC), ratio of solar heat (infrared) passing through the glass to incident solar heat
- Visible transmittance (VT), ratio of transmitted visible light divided by incident visible light
- Air leakage (AL), measured in cubic foot per minute per linear foot of crack between sash and frame
- Condensation resistance (CR), measured between 1 and 100 (the higher the number, the higher the resistance of the formation of condensation)
The European harmonised standard hEN 14351-1 which is dealing with doors and windows contains 23 characteristics (called Essential and non Essential ones). Another two preliminary European Norms are under preparation to deal with internal pedestrian doors (prEN 14351-2) and Smoke and/or fire resisting doors and openable windows (prEN 16034).
Window construction 
Grids or muntins 
These are the pieces of framing that separate a larger window into smaller panes. In older windows, large panes of glass were quite expensive, so muntins allowed smaller panes to fill a larger space. In modern windows, light-colored muntins still provide a useful function by reflecting some of the light going through the window, making the window itself a source of diffuse light (instead of just the surfaces and objects illuminated within the room). By increasing the indirect illumination of surfaces near the window, muntins tend to brighten the area immediately around a window and reduce the contrast of shadows within the room.
Frame and sash construction 
Frames and sashes can be made of the following materials:
|Material||thermal resistance||Durability||Maintenance||Cost||Recycled content||Comment|
|Wood||very good||variable||high||high||low||shrinks and swells with humidity changes|
|vinyl or PVC||very good||good*||low||low||very low|
|Aluminum||bad**||good||very low||low||typically > 95%||used in most large structures|
|Steel||medium||superior||very low||high||> 98%||typically welded at corner joints|
|Fiberglass||very good||very good*||very low||high||medium|
* Vinyl and fiberglass frames perform well in accelerated weathering tests. Because vinyl is not as strong as other materials, some vinyl frames are reinforced with metal or composite materials to improve their structural strength.
** Modern aluminium window frames are typically separated by a thermal break made of a polyamide. This greatly increases thermal resistance, while retaining virtually all of the structural strength.
Composites may combine materials to obtain aesthetics of one material with the functional benefits of another.
A special class of vinyl window frames, uPVC window frames, became widespread since the late 20th century, particularly in Europe: there were 83.5 million installed by 1998 with numbers still growing as of 2012.
Glazing and filling 
High thermal resistance can be obtained by evacuating or filling the insulated glazing units with gases such as argon or krypton, which reduces conductive heat transfer due to their low thermal conductivity. Performance of such units depends on good window seals and meticulous frame construction to prevent entry of air and loss of efficiency.
Modern double-pane and triple-pane windows often include one or more low-e coatings to reduce the window's U-factor (its insulation value, specifically its rate of heat loss). In general, soft-coat low-e coatings tend to result in a lower solar heat gain coefficient (SHGC) than hard-coat low-e coatings.
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.
Other construction details 
Many windows have movable window coverings such as blinds or curtains to keep out light, provide additional insulation, or ensure privacy. Windows allow natural light to enter, but too much can have negative effects such as glare and heat gain. Additionally, while windows allow the user to see the outside, there needs to be a way to maintain privacy on in the inside. Window coverings are practical accommodations for these issues.
Windows and the sun 
Sun incidence angle 
Historically, windows are designed with surfaces parallel to vertical building walls. Such a design allows considerable solar light and heat penetration due to the most commonly occurring incidence of sun angles. In passive solar building design, an extended eave is typically used to control the amount of solar light and heat entering the window(s).
An alternate method would be to calculate a more optimum angle for mounting windows which accounts for summer sun load minimization, with consideration of the actual latitude of the particular building. An example where this process has been implemented is the Dakin Building, Brisbane, California; much of the fenestration has been designed to reflect summer heat load and assist in preventing summer interior over-illumination and glare, by designing window canting to achieve a near 45 degree angle.
Solar window 
Photovoltaïc windows not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help generate electricity for the building. In most cases, translucent photovoltaïc cells are used.
Passive Solar 
Passive solar windows allow light and solar energy into a building while minimizing air leakage and heat loss. Properly positioning these windows in relation to the sun, wind, and landscape—while properly shading them to limit excess heat gain in summer and shoulder seasons, and providing thermal mass to absorb energy during the day and release it when temperatures cool at night—will increase a home's comfort and energy efficiency. These windows are more than decorative pieces of glass; when properly designed in climates with adequate solar gain, they can even serve as a building's primary heating system.
Window coverings 
A window covering is a shading or screening device that can be used for multiple purposes. For example, some window coverings are used to control solar heat gain and glare. Typically, there are external shading devices and internal shading devices. Low-e window film is a low-cost alternative to window replacement to transform existing poorly-insulating windows into energy-efficient windows.
For high-rise buildings, smart glass can be used as an alternative.
Classical Chinese window in Lan Su Chinese Garden
Arab-style windows in Jerusalem
A half-glazed window of the 17th century from Scotland
See also 
- / "Window". The Free Dictionary By Farlex. Retrieved 2012-05-19.
- "Understanding Window Terminology". Canada Mortgage and Housing Corporation. Retrieved 2012-05-19.
- "1828 Webster". 1828-dictionary.com. October 16, 2009. Retrieved 2010-05-02.
- "Window". Britannica. Retrieved 2012-05-19.
- Langley, Andrew (2011). Medieval Life. Eyewitness. Dorling Kindersley. p. 16. ISBN 1-4053-4545-4.
- Allen, Edward; Thallon, Rob (2011). Fundamentals of Residential Construction (3 ed.). Hoboken, NJ: Wiley. p. 654. ISBN 978-0-470-54083-1.
- "Will Tilt-and-Turn Windows Gain Market Share in North America? | Window & Door". Windowanddoor.com. 2010-03-29. Retrieved 2012-02-11.
- "Types of Skylights – All You Need to Know". Networx. Retrieved 2012-05-19.
- "Picture window". The Free Dictionary By Farlex. Retrieved 2012-05-19.
- "U.S. Dept. of Transportation: Safety information for bus/motorcoach passengers" (PDF). Retrieved 2012-02-11.
- "Stained glass". The Free Dictionary By Farlex. Retrieved 2012-05-19.
- "French Window". The Free Dictionary By Farlex. Retrieved 2012-05-19.
- Brett, Peter (2004). Carpentry and Joinery (2, illustrated ed.). Nelson Thornes. p. 255. ISBN 9780748785025.
- Windows and Heat Loss, NFRC Heat Loss Fact Sheet
- CPR guideline
- Carmody, J., Selkowitz, S., Lee, E. S., Arasteh, D., & Willmert, T. (2004). Window Systems for High-Performance Buildings. New York, NY: W. W. Norton & Company, Inc.
- Pritchard, Geoffrey (1999). Novel and Traditional Fillers for Plastics: Technology and Market Developments. iSmithers Rapra Publishing. p. 95. ISBN 9781859571835.
- "Global Vinyl Windows Market to Reach 163 Million Units by 2017, According to a New Report by Global Industry Analysts, Inc.". PRWeb. April 18, 2012. Retrieved 2012-02-11.
- Howell, Sandra C. (1976). Designing for the Elderly; Windows. Massachusetts Institute of Technology. Department of Architecture. Design Evaluation Project.
- "MIT opens new 'window' on solar energy". Web.mit.edu. 2008-07-10. Retrieved 2012-02-11.
- Beckett, H. E., & Godfrey, J. A. (1974). Windows: Performance, design and installation. New York, NY: Van Nostrand Reinhold Company.
|Wikimedia Commons has media related to: Windows|
- European Aluminium Association's publications dedicated to Buildings
- National Fenestration Rating Council (NFRC), a non-profit organization, administers an independent, uniform rating and labeling system for the energy performance of fenestration products. NFRC is the "engine" that drives virtually every window energy efficiency program in the country including ENERGY STAR (the U.S Government Sponsored Initiative).
- Roman Glass from Metropolitan Museum of Art
- The history of Metal Window
- The History Of the Box Sash Window
- Window Types
- Detailled informations on Window types