Understanding Window Muntins And Mullions

Window muntins and mullions are names that are often used interchangeably in window construction, if used at all. Many are unfamiliar with the terms as they are derived from old house construction techniques, even though modern houses make use of them today, albeit for decorative purposes.

You might recognize the general term used for window muntins and mullions: Grilles. However, this term is not technically correct, given they serve different purposes in window construction. Understanding the purpose of each is important before you order them for your home. 

What is a window mullion and how can one differentiate between it and the closely-named muntin

We unpack the two terms. 

What are Window Muntins? 

Muntins are most commonly used in reference to windows, but they are actually the term for any kind of vertical divider used for windows, doors, and even furniture. A window muntin is a strip of wood or metal that separates and holds panes of glass in a window, commonly termed as window pane dividers. The terms “window mutton” or “mutin” are also sometimes used, though erroneously.

The glass panes separated by the grid system created out of muntins are called “lights” or “lites”. In a piece of furniture such as a chair, a muntin is the main vertical piece of the framework. Their use in construction dates back as early as the 17th century when it was more affordable to make large windows and doors. It was also structurally necessary as early building’s walls could not carry weight when large windows were used. Muntins were used for support. 

Modern architecture allows for use of large windows, and fillets of wood are placed on top of the glass not as a fusion point but for decorative purposes. These are what many refer to as grilles.  

What Are Window Mullions?

A window mullion is a vertical division that breaks apart the opening of a window or door screen. It’s main purpose is to support the glazing of the window, which forms the watertight seal between your window’s glass and wood, or metal. It also offers support to the arch or a transom, which is the horizontal structural block above the window opening. 

Though mullion window frames can be made of any material, even glass, the most common are wood and aluminum. Stone mullions are even used to this day in Islamic and Armenian architecture, dating back to the 10th century. Think glassless courtyard window openings with a stone pillar in-between. It’s a common architectural feature in old buildings across Europe, not just for windows. 

Window mullion styles have since evolved and are normally used with large divided windows and doors. 

Window Mullions vs. Muntins

Even though we’ve answered the questions “what is a mullion” and “what is a muntin”, the difference only becomes clear when you put the two against each other. 

Both terms are used in window and door construction and describe dividing and joining glass and frames. The main difference is in what is being divided. Mullions divide the window or door opening into smaller blocks, while window muntins reinforce and join glass within a single window or frame. 

The mullion is the dividing piece between two or more window frames, while the muntin allows two or more glass panes to be joined together into a larger frame. Another difference is that mullions allow dissimilar items to be joined together, such as windows to doors. Mutins are primarily used only for fusing windows together.

 Mullion vs muntin, which do you need for your windows? If you’re looking for support and joining of different elements, mullions are what you should order. But if you’re looking to make a larger window out of panes of glass, or just want to have the design effect of divided windows, go with faux window muntins or order windows that come with them as a fusion point.  

Window Muntin Styles

Now that we have more clarity on the two window-construction features, let us look at some styles developed to create interesting designs using muntins. You can fashion your window with many different patterns, but these are the most commonly used: 

  • Rectangular 

This style divides each window into equally shaped and sized panes. They are influenced by colonial-style patterns, with 4-pane, 8-pane—or 4 over 4 in the case of double-hung windows.  

  • Prairie or Queen Anne

Unlike rectangular muntins, these are divided into unequal panes, lights. They feature a larger light in the middle and smaller squares in the corners. These are a contemporary or farmhouse style.

  • Sunburst or Starburst

This style features a combined-rectangular pattern with a half-round or quarter-round spoked top.

  • Diamond 

Where the window panes are divided into diamond-shaped lights by the muntins which are laid at an incline. There can be as many as 16 panes on these windows.  

Window designs greatly influence a building’s curb appeal, and muntins are a great way to compliment your home’s architectural style. 

If you’re looking for replacement windows in Kansas City, Bordner has many elegant grille patterns that are also customizable. You can achieve exactly the aesthetic you have in mind. Contact our team today to learn more!