What is the purpose of a mullion in a window or door structure?

The purpose of a mullion in a window or door structure is primarily to serve as a structural element that provides support, particularly when dealing with larger openings. Mullions are vertical or horizontal dividers that separate the different panes of glass in windows or the sections in doors. They add strength and stability to the overall configuration, ensuring that the structure can withstand environmental factors such as wind pressure and load from above. Additionally, they help maintain the integrity of the window or door by preventing excessive warping or deflection.

While decorative aspects and drainage functions may be associated with various components of a window or door system, their primary roles differ from that of a mullion. The focus on support highlights the critical structural role that mullions play in ensuring that larger glass panels can be installed safely without compromising the building's overall structural integrity.