Muntin vs Mullion: What's the Difference?

April 15, 2022



Muntin Vs Mullion Differences - Clera Windows + Doors

The main difference between a muntin and mullion is where they are placed on a window unit and what their purpose is.

Mullions are vertical shafts located in between windows. These elements offer structural support for the windows. Meanwhile, muntins are found on the window glass itself. They are vertical and horizontal elements that divide a window’s glass into a grid. Traditionally, muntins were a necessary part of the window to support the window glass. Nowadays, muntins are usually placed as decorative elements.  

This article is your ultimate guide on muntin vs mullion. Along the way, we will also cover how these window elements contribute to the home’s overall style and security.

Let’s begin!

Ultimate Guide On Muntin Vs Mullion - Clera Windows + Doors


What are Muntins in Windows?

Muntins are vertical and horizontal elements that divide the window glass into a grid. Muntins are also known as muntin bars, glazing bars, sash bars, or grilles.

Traditional Muntins

There is a reason why virtually all traditional windows have muntins. This is because muntins were necessary back then to hold together small pieces of glass. These windows are usually older, single-glazed windows that needed the muntin bars as support for the window’s glass pieces. These windows are also known as “true divided light” (TDL) windows.

Modern Muntins

Nowadays, not all windows have muntins. In fact, you are likely to find large window units with clear sheets of uninterrupted glass. These windows are perceived as “more modern” because they essentially are. Long ago, it was not possible to have muntin-free windows.

If you do find muntins in modern windows, it’s most likely that they were added for decorative purposes. Decorative muntins can be either resting on the exterior surface of the window glass or in between glass panes of double-glazed modern windows.

Either way, these modern muntins do not really separate the glass itself. In fact, the window glass in these modern windows is actually uninterrupted glass units that are typically multi-glazed. When muntins are applied this way, these are known as “simulated divided light” (SDL) windows.

Though these modern windows look like traditional windows and carry the same vintage charm, they offer more insulation and energy efficiency than their traditional counterparts.

Modern Muntins - Clera Windows + Doors

 What are Mullions on a Window?

Mullions are architectural elements that are found in between window units. Similar to muntins, traditional and modern mullions also have their differences. However, both versions of mullions offer rigid support for the window itself.

Traditional Mullions

Traditional mullions were made of stone and were major features found in Gothic architecture. These traditional mullions didn’t just support the windows; they also provided structural support and additional stability for windows or doors.

Modern Mullions

Unlike their traditional counterparts, modern mullions, are made of fibreglass, steel, aluminum, wood, or uPVC. Though not as structurally critical as traditional stone mullions, modern mullions are needed to provide support for window units that are placed side by side.

It is important to note that not all modern windows need mullions. For instance, if you have a sequence of double-hung windows with their own window openings, spaced many inches apart, it is likely that mullions are not necessary. However, if you have two or more windows placed side by side, then this combination window would likely need mullions.

For some modern windows, mullions are part of the entire window assembly. For example, some casement windows that are bought as a pair can have the mullion built-in.

Difference Between Muntin vs. Mullion - Clera Windows + Doors


Muntin vs Mullion

Now, let’s look at muntin vs mullion in terms of the practical and aesthetic benefits that each has to offer:

Aesthetic Benefits

Both mullions and muntins have roots in history. Muntins were highly prevalent in the 18th and 19th century, while mullions have their origins in gothic architecture (prior to the 10th century).

Though the use of mullioned windows dates back to an earlier period of time, they are actually quite versatile in terms of aesthetics. Mullions can be installed in virtually any type of house.

Muntins, on the other hand, bring a traditional or classic look to a property. Therefore, muntins are particularly appealing for owners of Craftsman homes, Victorian-style homes, classic/modern farmhouses, historical homes, and the like. For modern homes, however, muntins may not be as compatible because many people perceive them as a dated feature.

Home Security

Mullions do not offer much in terms of home security. Though they are structurally stronger than muntins, they will not stop a break-in. This is because mullions are in between window units — and breaking one of the windows is already enough for an intruder to access the house.

Muntins, on the other hand, may offer a bit of a boost to home security. If the grilles stay in place after the glass is broken, this can buy some precious time. However, since most muntins are decorative, it won’t take too much effort to actually break them.

Trying to Decide Between Muntins or Mullions for Your Windows?

This wraps up our guide on muntin vs mullion — two important elements to consider when getting new windows for your home. If you’re ready for a window upgrade, we’re here to help!

Clera Windows + Doors has been an industry leader in fenestration for over 40 years. We offer windows that have it all: durability, style, energy efficiency, and a wide range of customization options.

We can provide clear windows with uninterrupted glass or windows with muntins (or grilles). Our experts can also determine if mullions will be needed for larger combination windows for your home.

If you want to get started or have any questions in mind, please feel free to reach out!

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