Window Terminology: The Difference Between Muntins and Mullions

Window Terminology: The Difference Between Muntins and Mullions

Posted on November 21, 2012 By acarman


When you’re looking for new windows for your home, knowing as much as you can about windows will help you shop with confidence.  Knowing the proper terminology for the parts of a window will aid communication and understanding when you’re discussing different options for your home.

Two terms that are often confused with each other are “muntin” and “mullion.”  They refer to similar parts of the window, but once you know the difference it is easy to keep them straight.

A muntin is a strip of material, often wood, plastic, or aluminum, that holds panes of glass inside the larger frame of the window.  When window panes needed to be made of smaller pieces of glass, they were a necessary feature for holding the window together.  Today, muntins are more of a decorative feature for traditionally-styled homes rather than a necessary feature.

Additionally, today you will commonly see removable, single piece muntins as a design element to mimic the traditional look of individual lites. These one-piece muntins may be made of wood and snap over the single large piece of glass on the interior of a window to make it appear to be multiple smaller pieces of glass.

Permanently attached simulated divided lites are another design elements in today’s windows. Sierra Pacific Window’s interior simulite bars are made from clear Ponderosa Pine or Douglas Fir (or other species as requested) and  are available in either Colonial or Contemporary profiles in three widths: 7/8″, 1 5/16″ or 2″.  The exterior simulite bar is made of extruded aluminum on our clad product or the appropriate species of wood on our wood exterior products. Insulated units with simulite are standard with an internal shadow bar to give the appearance  of authentic divided lites.

Windows with Muntins

Mullions, on the other hand, refer to the joint where two or more windows are joined or “mulled” together. This joint may offer structural support between windows or may simply be an architectural design element.  Windows may be installed in a building as single units or as multiple units of two or more windows joined or “mulled” together in larger openings.

Windows with Mullions

For more information on buying new windows for your home, feel free to contact Sierra Pacific Windows at 888-612-9957 in Colorado and 800-824-7744 in the Western United States.