Bay window
Architectural element
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A window may be all three: projecting outward from the main fascia of a wall, curved in shape, and not reaching the ground. A bay window may be supported from the ground by a foundation, or in space by corbels, brackets, or cantilever.
A typical bay window consists of a central windowpane, called a fixed sash, flanked by two or more smaller windows, known as casement or double-hung windows. The arrangement creates a panoramic view of the outside, allows more natural light to enter the room, and provides additional space within the room. Bay windows are often designed to extend beyond the exterior wall, either adding to floor space, often filled with a table, desk, or seating area, or turned into a window seat (often with storage or a grated radiator below). They are found both in residential buildings, particularly in living rooms, studies, dining areas, or bedrooms, and in commercial and public structures.
Types
Bay window is a generic term for all protruding window constructions, regardless of whether they are curved like a bow window or angular, start from the ground, and run over one or multiple storeys.
In plan, the most frequently used shapes are isosceles trapezoid (which may be referred to as a canted bay window) and rectangle. But other polygonal shapes with more than three faces are also common, as are curved shapes. If a bay window is curved it may alternatively be called bow window. The angles most commonly used on the inside corners of the bay are 90, 135 and 150 degrees. Bay windows in a triangular shape with just one corner exist, but are relatively rare.
A bay window that does not reach the ground and is supported by a corbel, bracket, cantilever, or similar is called an oriel window.
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Uses
Bay windows can make a room appear larger, and provide views of the outside which would be unavailable with an ordinary flat window. They are found in terraced houses, semis, and detached houses as well as in blocks of flats.
In commercial structures bay windows allow an expanded footprint out into "public space", ideal for showroom windows; in multi-story commercial structures, particularly early skyscrapers, they increased a building's space without adding to its taxable footprint or expanding from the ground up into public space.
Based on British models, their use spread to other English-speaking countries like Ireland, the US, Canada, and Australia. Following the pioneering model of pre-modern commercial architecture at the Oriel Chambers in Liverpool, they feature on early Chicago School skyscrapers, where they often run the whole height of the building's upper storeys. They also feature in bay-and-gable houses commonly found in older portions of Toronto.
Particularly during the Gothic period bay windows often served as small house chapels, containing an altar and resembling an apse of a church. Especially in Nuremberg these are even called Chörlein (lit. 'little apse/choir'), with the most famous example being the one from the parsonage of St. Sebaldus Church.
In medieval times and up to the Baroque era most bay windows were oriels, and frequently appear as a highly ornamented addition to the building rather than an organic part of it.
In Islamic architecture, oriel windows such as the Arabic mashrabiya are frequently made of wood and in warm climates serve the general function of an enclosed balcony, providing greater privacy and relief from the sun.
Bay windows were identified as a defining characteristic of San Francisco architecture in a 2012 study that had a machine learning algorithm examine a random sample of 25,000 photos of cities from Google Street View.