A mullion is a metal channel that divides up two sides of an opening. A mullion can separate two pieces of glass, two door panels, or separate a door and a piece of glass.

When a mullion is used to separate two doors in a pair of doors, this mullion can be fixed or removable. A fixed mullion is an integral part of the door frame and cannot be removed. A removable mullion, on the other hand, is made so that it is secure to the door frame but can be disengaged and removed from the frame. This allows the full opening to be used for moving material through the pair of doors. With the mullion in place it will provide security and facilitate the flow of foot traffic through the opening.

Mullion with strikes

There are two types of hardware removable mullions that we will discuss in this blog post.

Standard Removable Mullions

Von Duprin Mullion

A standard removable mullion is made to attach to the head of the frame and sits so that it acts as a stop at the meeting edges of the doors. The mullion covers the gap between the doors and often has a “mullion seal” installed. This mullion seal will seal the gap between the face of the doors and the face of the mullion.

Mullions will usually have a mechanism that locks it securely in place once installed. When it needs to be removed, a hex key or other mechanism may be used to unlock and remove the mullion.

Cylinders and Keys

Keyed Removable Mullions

Keyed removable mullions are almost identical to standard removable mullions. The main difference is that instead of a hex key or mechanism, a keyed cylinder is installed. The keyed cylinder provides added security so that only those who have the cut key will be able to remove the mullion.


Additional Options

At some openings it may be desirable to install electric strikes. When these electric strikes have to be installed on the removable mullion it presents a unique requirement. Because the wiring must be run through the frame and down the inside of the mullion channel, a removable wire connector must be used. The removable mullion can be prepped for a wiring harness that connects the electric strikes to the power supply. When the mullion is removed, this wiring harness is disconnected as well and then reconnected when the mullion is replaced.

When an electric strike is needed, the handing of the for the strike must be indicated.

Mullions can also be prepped for certain strikes or provided blank if hardware is to be mounted at different heights than standard.

Fire rated mullions are also needed for fire rated openings where specified. These fire rated mullions may be more difficult to remove due to special fittings.