What is Mulling?

Definition of Mulling in Construction
Descriptive term for attaching two or more window or door units together to form a single assembly. To mull windows or doors, is to attach one to the other. The common side of two adjacent windows or doors is normally called the mullion and a mullion cover is used to cover the adjacent members. To mull together in construction is a term that means to join together in one common unit almost any number of construction elements. The facade of a structure that is all glass, is a number of window units, mulled together with mullion covers over the joints. There is no limitation to the number of units or the types of units that can be mulled together.