Mullion
Definition and meaning of Mullion in real estate.
A mullion is a heavy vertical or horizontal structural element that separates adjacent window units, doors, or panels, providing physical support to the opening. Unlike thin decorative strips, a mullion is a load-bearing part of the window or door frame assembly.
In more detail
Mullions are essential in architectural design for joining multiple window openings into a single, cohesive visual display. They support the weight of the windows above them and help the assembly resist wind pressure. In modern construction, mullions are often made of aluminum, steel, or wood, and they can be found in large storefronts as well as residential bay windows.
Home buyers should check the condition of wooden mullions during inspections, as they are susceptible to wood rot if the window seals fail and allow moisture to penetrate.
Key facts
| Category | Property Types & Construction |
|---|---|
| Applies to | Windows, doors, and glass panels |
| Watch out for | Wood rot and moisture damage at the joints |
| Primary function | Structural support and joining adjacent units |
An inspector notes that the wooden mullion separating the three double-hung windows in the living room has water damage and needs to be repaired to keep the window frames structurally secure.
Frequently asked questions
What is the difference between a mullion and a muntin?
A mullion is a thick structural bar that divides separate window frames, while a muntin is a thin strip that divides individual panes of glass within a single window frame.
Can a mullion be horizontal?
Yes, while mullions are most commonly vertical, they can run horizontally to separate a lower window from a transom window above it.