Mullion

Definition

A vertical element of a door or window frame that forms a division between units. The aluminum frame pieces, both horizontal and vertical, of a curtain wall panel. Structural element that divides adjacent window units.

Purpose

Mullions provide structural support and division between adjacent window or door units, allowing for larger openings and multiple panes or panels. They enhance the aesthetic appeal and functionality of the frames.

Examples of Use

• Windows: Using mullions to divide large window openings into smaller, manageable panes.
• Curtain walls: Incorporating mullions into the design of curtain walls to support the glass panels and create a uniform appearance.
• Doors: Adding mullions to French doors or other multi-pane doors for structural support and visual interest.

Related Terms

• Muntin: A small vertical or horizontal bar that divides individual panes of glass within a window sash.
• Sash: The frame that holds the panes of a window and fits within the window frame.
• Transom: A horizontal structural element or window above a door or window.

Notes

• Mullions can be made from various materials, including wood, aluminum, steel, and fiberglass, depending on the desired strength and appearance.
• They play a critical role in the structural integrity of large window and curtain wall systems.
• Proper sealing and insulation around mullions are essential to prevent air and water infiltration.