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 A window is an opening in a wall (or other 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 in.

Types of windows:

This sash window is 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 (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 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.

Awning window

An awning window is a casement window that is hung horizontally, hinged on top, so that it swings outward like an awning.

Hopper window

A hopper window is a bottom hung casement window that opens similar to a draw bridge typically opening to the outside.

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.

Transom window

A window above a door; if an exterior door the transom window is often fixed, if an interior door it can often open either by hinges at top or bottom, or can rotate about hinges at the middle of its sides. It provided ventilation before forced air heating and cooling. A transom may also be known as a fanlight, especially if it is fan-shaped, particularly in the British Isles.

Double-hung sash window
Double-hung sash window

 Jalousie window

Also known as a louvered window, the jalousie window is comprised 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.

Clerestory window

A vertical window set in a roof structure or high in a wall, used for daylighting.


A flat or sloped window used for daylighting, built into a roof structure that is out of reach.

Roof window

A sloped window used for daylighting, built into a roof structure that is within reach.

Roof lantern or Cupola

A roof lantern is a multi-paned glass structure, resembling a small building, built on a roof for day or moon light. Sometimes includes an additional clerestory. May also be called a cupola.

Jalousie or louvered window
Jalousie or louvered window

Bay Window

A multi-panel window, with at least three panels set at different angles to create a protrusion from the wall is commonly used in cold country where snow often falls. The panels are thus set in three different directions,from where a person would have a view from the interior of a building.

Bay window
Bay window

Oriel window

A window with many panels. It is most often seen in the typical Tudor-style house and monasterie. An oriel window projects from the wall and does not extend to the ground. Oriel windows originated as a form of porch. They are often supported by brackets or corbels. Buildings in the Gothic Revival style often have oriell windows.

Thermal window

Thermal, or Diocletian, windows are large semicircular windows (or niches) which are usually divided into three lights (window compartments) by two vertical mullions. The central compartment is often wider than the two side lights on either side of it.

Fixed window

A window that cannot be opened, whose function is limited to allowing light to enter. Clerestory windows are often fixed. Transom windows may be fixed or operable.

Picture window

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.

Multi-lit window / divided-lite window

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, this was the prevailing style of window until the beginning of the twentieth century, and is traditionally still used today.

Emergency exit window / egress window

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 window

A window composed of pieces of colored glass, transparent 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 Victorianhouses and some Wrightian houses, and are especially common in churches.

French window

A French window, also known as a French door is really a type of door, but one which has one or more panes of glass set into the whole length of the door, meaning it also functions as a window.

Super window

A popular term for highly insulating window with a heat loss so low it performs better than an insulated wall in winter, since the sunlight that it admits is greater than its heat loss over a 24 hour period. 

Window construction

Windows can be a significant source of heat transfer[2]. Insulated glazing units therefore consist of two or more panes to reduce the heat transfer.


Frame and sash construction

Frames and sashes can be made of the following materials:

* Vinyl and fiberglass frames have not been around for long enough to assess their long-term durability. Because vinyl is not as strong as other frames, some vinyl frames are reinforced with metal; however, this will reduce the thermal efficiency of a vinyl window frame.

** Modern metal window frames typically consist of two surfaces separated by a thermal break made of an insulating spacer material. While this can double thermal resistance, it is still less than half of that of other frames.

Composites may combine materials to obtain aesthetics of one material with the functional benefits of another.

Glazing and filling

Low-emissivity coated panes reduce heat transfer by radiation, which, depending on which surface is coated, helps prevent heat loss (in cold climates) or heat gains (in warm climates).

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 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 and the sun

Main article: Daylighting

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:

Photovoltaics are best known as a method for generating electric power by using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays to convert energy from the sun into electricity. To explain the photovoltaic solar panel more simply, photons from sunlight knock electrons into a higher state of energy, thereby creating electricity. The term photovoltaic denotes the unbiased operating mode of a photodiode in which current through the device is entirely due to the transduced light energy. Virtually all photovoltaic devices are some type of photodiode.

Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC. There is a smaller market for off grid power for remote dwellings, roadside emergency telephones, remote sensing, and cathodic protection of pipelines.

Cells require protection from the environment and are usually packaged tightly behind a glass sheet. When more power is required than a single cell can deliver, cells are electrically connected together to form photovoltaic modules, or solar panels. A single module is enough to power an emergency telephone, but for a house or a power plant the modules must be arranged in arrays. Although the selling price of modules is still too high to compete with grid electricity in most places, significant financial incentives in Japan and then Germany and Italy triggered a huge growth in demand, followed quickly by production.

Perhaps not unexpectedly, a significant market has emerged in off-grid locations for solar-power-charged storage-battery based solutions. These often provide the only electricity available.

The EPIA/Greenpeace Advanced Scenario shows that by the year 2030, PV systems could be generating approximately 2,600 TWh of electricity around the world. This means that, assuming a serious commitment is made to energy efficiency, enough solar power would be produced globally in twenty-five years’ time to satisfy the electricity needs of almost 14% of the world’s population.

Solar windows not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help generate electricity for the building.[

Stained glass skylight and window, Auckland Museum
Stained glass skylight and window, Auckland Museum