Mullion
Mullions are members that form vertical divisions between units of a window, door, screen or glass curtain wall. Together with horizontal members known as transoms they provide rigid support to glazing.
A mullion wall is a structural system whereby the load of the floor slab is taken by prefabricated panels around the perimeter.
They can be used for decorative purposes, or to allow the combination of smaller window units into larger compositions, or to provide structural support to an arch or lintel. They can also be used as an element in door frames to divide an opening and allow two separate doors to be accommodated by a single frame.
The use of mullions dates back to before the 10th century. As the use of glass for windows became widespread, so did the use of mullions, as they allow larger openings to be sub-divided into smaller windows which are technically easier to manufacture and less expensive.
They can be found in Armenian, Saxon and Islamic architecture. They became more commonly used to divide paired windows in Romanesque architecture, as well as open arcades. The use of stone mullions in Gothic architecture increased both in terms of size and complexity, as they were used both structurally and ornamentally, particularly in churches for stained glass windows.
Modern mullions are commonly made from materials such as timber, aluminium, steel and UPVC.
The word 'mullion' is also commonly used to describe vertical members between panes of glass within a window assembly (rather than between window units). These smaller members are sometimes referred to as 'muntins'.
[edit] Related articles on Designing Buildings
Featured articles and news
Specifying rendered external wall insulation for fire safety
How to interrogate the evidence provided to the specifier.
The benefits of writing articles for your organisation
How to create a profile for your organisation and publish for free.
No Falls Week. The importance of safe working at height
What to expect and what is on offer to avoid accidents.
Scottish Government action to reach net-zero targets
Retrofit expert group highlight critical actions needed.
A forward thinking, inclusive global community of members.
From engineered product life-spans, to their extension.
Circular economy in the built environment
A brief description from 2021. Where are we now?
Mental Health Awareness Week with ABS
Architects Benevolent Society programme of activity.
CLC publishes domestic retrofit competency framework
Roadmap of Skills for net zero.
May 13-19: Moving more for our mental health.
Understanding is key to conservation.
Open industry engagement survey seeks responses
Institutions and the importance of engagement.
National Retrofit Hub unveils new guide
Digital Building Logbooks and Retrofit: An Introduction.
Enhancing construction site reporting efficiency
Through digitisation and the digital revolution.