Mullion
Encyclopedia
A mullion is a vertical structural element which divides adjacent window
units. The primary purpose of the mullion is as a structural support to an arch or lintel above the window opening. Its secondary purpose may be as a rigid support to the glazing of the window. When used to support glazing, they are teamed with horizontal supporting elements called "transoms".
In the commercial door industry, the term is also applied to a piece of hardware that divides the opening of a pair of doors.
, with paired windows divided by a mullion, set beneath a single arch becoming a fashionable architectural form. The same structural form was used for open arcades as well as windows, and is found in galleries and cloisters.
In Gothic architecture
windows became larger and arrangements of multiple mullions and openings were used, both for structure and ornament. This is particularly the case in Gothic churches where stained glass is set in lead and ferramenta between the stone mullions. Mullioned windows of a simpler form continued to be used into the Renaissance and various Revival styles.
and aluminum are most common, although glass is also used between windows. I.M. Pei, in his design of JFK Airport's Terminal 6 (National Airlines Sundrome
) used all-glass mullions, unprecedented at the time.
Mullions are vertical elements and are often confused with transoms
, which lie horizontally. The word is also confused with the "muntin
" (or "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, and it carries the dead load of the weight above the opening and the wind load acting on the window unit back to the building structure. The term is also properly applied to very large and deep structural members in many curtain wall
systems.
When a very large glazed area was desired before the middle of the nineteenth century, such as in the large windows seen in Gothic
churches or Elizabethan 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 came
s 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.
Window
A window is a transparent or translucent opening in a wall or door that allows the passage of light and, if not closed or sealed, air and sound. Windows are usually glazed or covered in some other transparent or translucent material like float glass. Windows are held in place by frames, which...
units. The primary purpose of the mullion is as a structural support to an arch or lintel above the window opening. Its secondary purpose may be as a rigid support to the glazing of the window. When used to support glazing, they are teamed with horizontal supporting elements called "transoms".
In the commercial door industry, the term is also applied to a piece of hardware that divides the opening of a pair of doors.
History
Stone mullions were used in Armenian, Saxon and Islamic architecture prior to the 10th century. They became common across Europe in the Romanesque architectureRomanesque architecture
Romanesque architecture is an architectural style of Medieval Europe characterised by semi-circular arches. There is no consensus for the beginning date of the Romanesque architecture, with proposals ranging from the 6th to the 10th century. It developed in the 12th century into the Gothic style,...
, with paired windows divided by a mullion, set beneath a single arch becoming a fashionable architectural form. 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
Gothic architecture is a style of architecture that flourished during the high and late medieval period. It evolved from Romanesque architecture and was succeeded by Renaissance architecture....
windows became larger and arrangements of multiple mullions and openings were used, both for structure and ornament. This is particularly the case in Gothic churches where stained glass is set in lead and ferramenta between the stone mullions. Mullioned windows of a simpler form continued to be used into the Renaissance and various Revival styles.
Design
Mullions may be made of any material, but woodWood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
and aluminum are most common, although glass is also used between windows. I.M. Pei, in his design of JFK Airport's Terminal 6 (National Airlines Sundrome
Sundrome
The Sundrome was the name for the terminal of National Airlines at John F. Kennedy International Airport. It was designed by I. M. Pei & Partners . Opened in 1970, it is now known as Terminal 6...
) used all-glass mullions, unprecedented at the time.
Mullions are vertical elements and are often confused with transoms
Transom (architectural)
In architecture, a transom is the term given to a transverse beam or bar in a frame, or to the crosspiece separating a door or the like from a window or fanlight above it. Transom is also the customary U.S. word used for a transom light, the window over this crosspiece...
, which lie horizontally. The word is also confused with the "muntin
Muntin
Muntin or Muntin bar is a strip of wood or metal separating and holding panes of glass in a window. Muntins are also called "glazing bars", "muntin bars", or "sash bars". Muntins can be found in doors, windows and furniture, typically in western styles of architecture...
" (or "glazing bar" in the UK) which is the precise word for the very small strips of wood or metal that divide a sash
Sash window
A sash window or hung sash window is made of one or more movable panels or "sashes" that form a frame to hold panes of glass, which are often separated from other panes by narrow muntins...
into smaller glass "panes" or "lights".
A mullion acts as a structural member, and it carries the dead load of the weight above the opening and the wind load acting on the window unit back to the building structure. The term is also properly applied to very large and deep structural members in many curtain wall
Curtain wall
A curtain wall is an outer covering of a building in which the outer walls are non-structural, but merely keep out the weather. As the curtain wall is non-structural it can be made of a lightweight material reducing construction costs. When glass is used as the curtain wall, a great advantage is...
systems.
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 architecture
Gothic architecture is a style of architecture that flourished during the high and late medieval period. It evolved from Romanesque architecture and was succeeded by Renaissance architecture....
churches or Elizabethan 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
Sash window
A sash window or hung sash window is made of one or more movable panels or "sashes" that form a frame to hold panes of glass, which are often separated from other panes by narrow muntins...
or casement to be further subdivided by muntins or lead came
Came
A came is a divider bar used between small pieces of glass to make a larger glazing panel, sometimes referred to as leaded glass. This process is then referred to as "leading". Cames are mostly made of soft metals such as lead, zinc, copper or brass. They generally have an H-shaped cross section,...
s 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
- CameCameA came is a divider bar used between small pieces of glass to make a larger glazing panel, sometimes referred to as leaded glass. This process is then referred to as "leading". Cames are mostly made of soft metals such as lead, zinc, copper or brass. They generally have an H-shaped cross section,...
- Glass mullion systemGlass mullion systemGlass mullion system is a glazing system in which sheets of tempered glass are suspended from special clamps, stabilized by perendicula stiffeners of tempered glass, and joined by a structural silicone sealant or by metal patch plates.-Notable buildings:...
- Mullion wallMullion wallA mullion wall is a structural system in which the load of the floor slab is taken by prefabricated panels around the perimeter. Visually the effect is similar to the stone mullioned windows of Perpendicular Gothic or Elizabethan architecture....
- MuntinMuntinMuntin or Muntin bar is a strip of wood or metal separating and holding panes of glass in a window. Muntins are also called "glazing bars", "muntin bars", or "sash bars". Muntins can be found in doors, windows and furniture, typically in western styles of architecture...
- Stained glassStained glassThe term stained glass can refer to coloured glass as a material or to works produced from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant buildings...
- TransomTransom (architectural)In architecture, a transom is the term given to a transverse beam or bar in a frame, or to the crosspiece separating a door or the like from a window or fanlight above it. Transom is also the customary U.S. word used for a transom light, the window over this crosspiece...