FAQ Knowledge Articles

A mullion, or mull, is the vertical member of a sash, window or door frame between openings in a multiple-opening frame including:

1. SPACE MULL - Two or more units mulled together with a space left between the units. The jamb extension surrounds the entire unit.

2. STUD POCKET - Two or more units mulled together with a space between the units. The jamb extension surrounds each unit separately, providing space for a support member between the units.