Mullion

A structural element that is used to enhance the bearing capacity of a wide frame. The joints with the frame should be characterized by increased strength.

Simply put, the mullion breaks the span of the opening to reduce the load on the lintel. In concrete or brick houses, mullion does not make sense for reinforcement. It is used only to simplify the manufacture of windows with movable panes, for example, to create a narrow casement that is used for ventilation.

Mullion was often used in wooden houses or windows with transoms if the transom is operable. In this case, for fastening the transom, a horizontal impost is inserted into the window frame. In a wooden frame house, lintels are made of timber or twin boards. Timber and boards tend to bend or twist. To reduce the effect on the window frame, mullions are used, which additionally strengthen the lintel.