what is a mullion

Door Frames and Mullions – Fixed vs. Removable

Doors | Frames | Hardware

A mullion is a fixed or removable part of the frame which separates door leaves, a door and sidelites, glazed areas, or paneled areas. Hollow metal mullions allow for the prepping of strikes for all different types of locks including deadbolts, cylindrical locks, mortise locks, and rim or mortise exit devices. Some mullions can even accept electric strikes.


What is a Fixed Mullion?

A fixed mullion between two door leaves is used to separate a pair of doors into a bank, allowing for single door performance in double door openings. The fixed mullion is welded to the frame head, meaning it cannot be removed. During installation, the fixed mullion is anchored to the floor at the base of the mullion.

fixed mullion

What is a Removable Mullion?

Removable mullions can also be installed to allow for single door performance in double door openings. They are mechanically attached to the underside of the frame head and to the floor. The benefit of removable mullions is that they can be temporarily removed to utilize the entire width of the opening for the movement of furniture or large equipment. Keep in mind, for the doors to operate normally the removable mullion must be put back in place.

removable mullion

Removable mullions are available in styles that are mounted between-the-door for standard operating hardware or as a post mounted behind a pair of doors (on the push side) for use with rim exit devices on each leaf. Both types are available as keyed and/or fire rated. Some can also be prepped for electrified hardware.

Between-the-Door Mullion

between-the-door mullion

Post Type Mullion

post-type mullion

Both fixed and removable mullions that are used with double doors can help secure an opening and can lead to less maintenance over time. However, due to some building codes, not all double door openings are appropriate for fixed or removable mullions; it is important to contact an expert prior to installation.

To learn more, check out Lori Greene’s article and video about mullions.

What is the Difference Between a Mullion and a Muntin?

Unlike mullions, which are a part of the frame, muntins are bars or formed material supplied by the glazier as a decorative piece or to support separate panes of glass used within a door, sidelite, transom, borrowed lite, or window frame. Muntins are not commonly found in commercial construction.


Custom Commercial Doors and Frames

At LaForce, we know that commonly used doors and frames do not always fit the need or design of a building. Our manufacturing facilities allow us to create custom doors and frames in-house that meet code requirements and can match your building’s appearance. Additionally, these capabilities can help control our lead times and even provide expedited options. We can manufacture, design, or modify custom doors and frames including hollow metal, stainless steel, aluminum (modify only), wood (modify only), fire rated, and lead lined metal.

Have a question or concern about your next building project? Contact one of our experts today – we’re always glad to help!