Although the historic use of glass dates back to the Romans, glass windows only became common domestically in England in the early 17th century, gradually becoming more versatile and widespread as plate glass processes were perfected during the Industrial Age.
England, France, Ireland and Scotland introduced a window tax during the 18th and 19th centuries which was payable based on the number of windows in a house. It is still common to see buildings from that period with windows that were bricked-up to avoid the tax. The tax was repealed in 1851.
Windows are can include a number of different components:
- Light: The area between the outer parts of a window, usually filled with a glass pane.
- Frame: This holds the light in place and supports the window system.
- Lintel: A beam over the top of a window.
- Jamb: The vertical parts forming the sides of the frame.
- Sill (or cill): The bottom piece in a window frame, often projecting beyond the line of the wall.
- Mullion: A vertical element between two window units or lights.
- Transom: A horizontal element between two window units or lights.
- Head: The uppermost member of the frame.
- Sash: The frame holding the glazing.
- Casement: A window (or sash) attached to its frame by one or more hinges.
It is important that windows be made of suitable and durable materials:
- With good thermal and sound insulation properties.
- Capable of resisting wind, and rain.
- Easy to clean.
- Providing safety and security.
Most styles of windows are available in a number of different materials. Traditionally, windows were made of timber, either hardwood or softwood, and often protected against decay using paint or a natural wood finish. This finish requires regular maintenance.
The efficiency of windows is improved by double glazing, treble glazing, low-e coatings, the construction of the frame, the type of glass, the gas used to fill the sealed unit and so on. Generally, more efficient windows are more expensive, but the capital cost may be recovered during the life of the window life through lower energy bills. In addition, the conditions within the enclosed space are likely to be more comfortable.
The BFRC Window Energy Rating (WER) scheme is based on a traffic-light style A-G ratings system for energy efficiency similar to that used for fridges, washing machines, cookers and so on. An A rating indicates a good level of energy efficiency, whilst G is the lowest possible rating.
 Opening type
 Fixed light
A window that is fixed in place and cannot be opened. Often used where light or vision alone is required rather than ventilation, but fixed lights are commonly used in conjunction with other openable types of window.
 Vertical slider / sash
Glass is fitted in ‘sashes’ (moveable panels) that slide vertically past each other:
- Single-hung sash: One sash is moveable and the other is fixed.
- Double-hung sash: Sashes are hung on spring balances or counterweights and made up of two sashes that overlap slightly and slide up and down vertically inside the frame.
- Horizontal sliding sash: Two sashes that overlap slightly and slide horizontally on guide rails within the frame.
An opening window fixed to the frame by hinges along one of its edges:
- Side hung casement: The sash side opens outwards.
- Top hung casement: The sash top opens outwards. Also known as awning windows.
- Bottom hung casement: The sash bottom opens inwards. Also known as hopper windows.
Casement windows preceded sash windows in the UK and traditionally opened inwards, although now they more commonly open outwards so as to free space inside and better direct air inwards for ventilation.
Casement windows require a metal bar called a ‘stay’ to hold them open. Different types are available such as the peg type (the stay has holes along it which allow it to fit over pegs), telescopic (tube shaped), and friction (a bent arm allows the window to open to 180-degrees).
 Tilt and turn
Tilt and turn windows Include a mechanism that allows them to tilt inwards from one edge or to open inwards from one side. The stability of the mechanism allows tilt and turn windows to be larger than casement windows. They are also easy to clean from the inside.
Pivot windows are hung on one hinge at centre points on each of two opposite sides. This allows the window to revolve when opened. The pivots can either be vertical, with the hinges mounted top and bottom, or horizontal, with the hinges mounted at each jamb. Pivot hinges incorporate a friction device that enables the window to hold itself open against its own weight. Pivot windows tend to be more expensive than casement windows but can allow for easy cleaning access.
These are made up of a number of individual sashes, usually 2, 3 or 4, hinged together. They can be opened up in a concertina style and stacked neatly against each other at the side of the window frame.
These windows use a series of parallel pieces of glazing that are hung on centre pivots positioned at intervals down the vertical jambs that allow them to open and close using a crank or lever. They allow for good ventilation with only small projections.
 Other types
- Tilt and slide: The sash tilts inwards at the top and slides horizontally behind the fixed pane.
- Toplight: These are usually above doors.
- Sidelight: Positioned beside a door or main window.
- Skylight or rooflight: These are windows positioned in the roof. The brand name ‘Velux’ has become associated with opening domestic rooflights.
- Clerestory: Bands of windows across the tops of buildings that allow natural light in without compromising privacy or security.
- Bay: Multi-panel windows that project in front of the external wall line, being supported by a sill height wall.
- Bow: A curved bay window.
- Multi-lite: Windows glazed with small panes of glass separated by glazing bars, or muntins.They can be arranged decoratively to suit aesthetic needs or architectural styles.
- Stained glass: Decorative windows made of coloured glass separated by glazing bars, popular in churches and Victorian houses.
- Topguided: Tracks and slides enable the top to slide downwards whist the bottom opens out.
- Sidehung: A variation on a casement window, side opening controlled by tracks and slides.
- Dormer: A small roofed structure that projects outwards from the main pitched roof of a building. See Dormer window for more information.
For more information, see Domestic windows.
 Related articles on Designing Buildings Wiki:
- Approved Document K.
- BFRC window rating scheme.
- Controlled fitting.
- Curtain wall systems.
- Curved glass.
- Daylit space.
- Domestic windows.
- Dormer window.
- Double glazing.
- Low-E glass.
- Rights to light.
- Secondary glazing.
- Transparent insulation materials.
- Window energy rating.
 External references
- ‘Building Construction Handbook’ (6th ed.), CHUDLEY, R., GREENO, R., Butterworth-Heinemann (2007)
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