- Articles about other meanings include Window codename (In the 2nd World War), Window (astronomy), window (computing), windowing system, or X Window System.
A window is an opening in an otherwise solid, opaque surface through which light 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.
Opening in wall
Very early windows were shielded with hide or cloth stretched over the opening or wooden shutters. Later, two 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, and paper windows. 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.
Today a window can be made in any shape and size desired.
Modern windows come in many styles. These include:
- Double-hung sash window: The traditional style of window, with two parts (sashes) that overlap slightly and slide up and down inside the frame.
- Single-hung sash window: one sash is moveable and the other fixed.
- Sliding window: has two or more sashes that overlap slightly but slide horizontally within the frame.
- Casement window: A window that turns out at an angle, staying fixed along one side, usually opened using a crank.
- Vent Window: Like a casement window but with the hinge at the top or bottom.
- Tilt and slide: a window combining the opening options of a casement and a sliding window.
- Tilt and turn: a window combining the opening options of a casement and vent window.
- 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. (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.
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.
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.
Many windows have movable window coverings to keep out light, provide additional insulation, or ensure privacy.