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A mullion is a vertical element that forms a division between units of a window or screen, or is used decoratively. It is also often used as a division between double doors. When dividing adjacent window units its primary purpose is a rigid support to the glazing of the window. Its secondary purpose is to provide structural support to an arch or
lintel A lintel or lintol is a type of beam (a horizontal structural element) that spans openings such as portals, doors, windows and fireplaces. It can be a decorative architectural element, or a combined ornamented structural item. In the case o ...
above the window opening. Horizontal elements separating the head of a door from a window above are called transoms.


History

Stone mullions were used in Armenian,
Saxon The Saxons ( la, Saxones, german: Sachsen, ang, Seaxan, osx, Sahson, nds, Sassen, nl, Saksen) were a group of Germanic * * * * peoples whose name was given in the early Middle Ages to a large country ( Old Saxony, la, Saxonia) near the No ...
and
Islamic architecture Islamic architecture comprises the architectural styles of buildings associated with Islam. It encompasses both secular and religious styles from the early history of Islam to the present day. The Islamic world encompasses a wide geographic ...
prior to the 10th century. They became a common and fashionable architectural feature across Europe in
Romanesque architecture Romanesque architecture is an architectural style of medieval Europe characterized by semi-circular arches. There is no consensus for the beginning date of the Romanesque style, with proposals ranging from the 6th to the 11th century, this lat ...
, with paired windows divided by a mullion, set beneath a single arch. The same structural form was used for open arcades as well as windows, and is found in galleries and cloisters. In
Gothic architecture Gothic architecture (or pointed architecture) is an architectural style that was prevalent in Europe from the late 12th to the 16th century, during the High and Late Middle Ages, surviving into the 17th and 18th centuries in some areas. I ...
windows became larger and arrangements of multiple mullions and openings were used, both for structure and ornament. This is particularly the case in Gothic cathedrals and churches where stained glass was set in lead and ferramenta between the stone mullions. Mullioned windows of a simpler form continued to be used into the
Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass id ...
and various Revival styles. Italian windows with a single mullion, dividing the window into two equal elements are said to be biforate, or to parallel the Italian bifore windows.


Design

Mullions may be made of any material, but
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of ligni ...
and
aluminium Aluminium (aluminum in AmE, American and CanE, Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately o ...
are most common, although glass is also used between windows. I. M. Pei used all-glass mullions in his design of JFK Airport's Terminal 6 ( National Airlines Sundrome), unprecedented at the time. Mullions are vertical elements and are often confused with transoms, which lie horizontally. In US parlance, the word is also confused with the " muntin" ("glazing bar" in the UK) which is the precise word for the very small strips of wood or metal that divide a sash into smaller glass "panes" or "lights". A mullion acts as a structural member, in most applications the mullion transfers wind loads and weight of the glazing and upper levels into the structure below. In a curtain wall screen, however, the mullions only support the weight of the transoms, glass and any opening vents. Also in the case of a curtain wall screen the weight of glazing can be supported from above (providing the structure can take the required loads) this puts the mullions under tension rather than compression. When a very large glazed area was desired before the middle of the nineteenth century, such as in the large windows seen in
Gothic Gothic or Gothics may refer to: People and languages *Goths or Gothic people, the ethnonym of a group of East Germanic tribes **Gothic language, an extinct East Germanic language spoken by the Goths **Crimean Gothic, the Gothic language spoken b ...
churches or
Elizabethan The Elizabethan era is the epoch in the Tudor period of the history of England during the reign of Queen Elizabeth I (1558–1603). Historians often depict it as the golden age in English history. The symbol of Britannia (a female personif ...
palaces, the openings necessarily required division into a framework of mullions and transoms, often of stone. It was further necessary for each glazed panel, sash or casement to be further subdivided by muntins or lead cames because large panes of glass were reserved primarily for use as mirrors, being far too costly to use for glazing windows or doors. In traditional designs today, mullions and transoms are normally used in combination with divided-light windows and doors when glazing porches or other large areas.


See also

* Bifora, a mullioned window * Trumeau – for a door * Mullion wall


Notes


References

* Architectural elements Windows {{interwiki extra, qid=Q1291476