A window is an opening in an otherwise solid, opaque surface through which light and sometimes air can pass. For example, a window in the wall of a house, or a window in a scientific measurement device that permits reading of certain wavelengths.
Window is also used metaphorically to refer to a time period during which something can occur and outside of which the thing cannot occur, as in a window of opportunity to launch a rocket to the moon on the most efficient trajectory.
The word Window dates back to Old Norse "Wind Eye"; opening to the air.
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Opening in wall
A window is an opening in the wall of a building that allows light and air to enter a room and people to see out. At previous times in history they were merely small oval or square holes in the walls.
Very early windows were shielded with hide or cloth stretched over the opening or wooden shutters. Later, three types of windows were invented that allowed light but not weather to pass into a building: mullioned glass windows, which joined multiple small pieces of glass with leading, paper windows, and windows made of 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. 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 glassed-in rectangles or squares. Churches traditionally have stained glass windows.
Today a window can be made in any shape and size desired.
Window styles
Modern domestic windows come in many styles. The choice of design varies thoughout 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 - eg England. Continental climates tend to have larger windows, many of which open inwards - eg France and Germany. Styles available include:
- Double-hung sash window: The traditional style of window in the uSA, with two parts (sashes) that overlap slightly and slide up and down inside the frame.
- Single-hung sash window: one sash is movable and the other fixed.
- Horizontal Sliding sash window: has two or more sashes that overlap slightly but slide horizontally within the frame.
- Casement window: An outward-opening window comprising either a side-hung or top-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.
- Tilt and slide: a window where the sash tilts inwards at the top and then slides horizontally behind a fixed pane.
- Tilt and turn: a window which can either tilt inwards at the top, or can open inwards hinged at the side.
- Jalousie window: A window comprising many slats of glass that open and close like a Venetian blind, usually using a crank. 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.
- Skylight: A flat or sloped window built into a roof structure for daylighting
- Bay window: A multipanel window, with at least three panels set at different angles to create a protrusion from the wall line.
- Oriel window
- Fixed window: A window that cannot be opened. A non-openind window is sometimes called a "light" because its function is limited to allowing light to enter without any outside air. (Clerestory windows are often fixed.)
- Picture window: A very large fixed window in a wall, intended to provide an unimpeded view as if framing a picture.
A replacement window is a framed window designed to slip inside the original window frame from the inside after the old sashes are removed (USA). Alternatively it is a complete window including a replacement outer frame (Europe).
A new construction window is a window with a nailing fin designed to be inserted into a rough opening from the outside before applying siding and inside trim (USA). In Europe, many 'new build' windows are used as templates, and bricks are laid up to the frame.
Window materials
Modern windows have insulated glazing, called insulated glass when made from glass, which is usually double paned but might be triple paned.
Modern windows are made from large sheets of glass while windows in the past were made from multiple panes held together by a grille within the sash, also called muntin bars or mullions. Today, decorative muntin bars are attached on the surface of the glazing or sandwiched between the panes of the insulated glazing. Most companies use the term grille for the set of decorative muntin bars within a sash.
Frames and sashes were traditionally made of wood, but metal, vinyl, and composites are also common. Solid metal frames and sashes are inefficient because metal conducts heat and cold. Some frames are made of vinyl-clad or aluminum-clad wood. Modern metal window parts consist of two halves separated by insulating spacer.
The terms "single-light" or "double-light" (or "'more'-light") refer to the number of glass panes in a window.
The beam or arch over the top of a window is known as the lintel or transom.
Many windows have movable window coverings to keep out light, provide additional insulation, or ensure privacy.