FAQ Knowledge Articles

Definition of Mulling: The act of attaching two or more window or door units together.  The joint is then finished with a mullion center cap or mull trim.

Frame to frame: Units mulled together with no space between the frames.

Space mull: Two or more units mulled together with a space between the units.  The jamb extension surrounds the entire assembly.

Stud pocket: Two or more units mulled together with a space between the units.  Jamb extension surrounds each unit separately, providing space for a support member between the units.

Mull reinforcement: A system of high strength material between the units of an assembly.  Those include a 3/8" piece of aluminum, 1" LVL (laminated veneered lumber) and various tube mullion options.  This adds strength and stability to large assemblies.

For more information, see:
What is a mullion?
What are the mulling guidelines for Integrity product?
Mulls - Architectural Details Manual chapter