What Is A Door & Window Mullion?

Key Takeaways

• A mullion is a vertical or horizontal element that forms a division between units of a window or door.
• Mullions provide structural support and can be made from various materials like wood, metal, or vinyl.
• They are different from muntins, which divide glass panes within a window sash.
• Choosing the right mullion material depends on factors like durability, aesthetics, and maintenance.
• We provide customized windows and doors for both residential and commercial use.

What Is A Door And Window Mullion

Mullions and muntins are not the same as you can see in the image above.

A mullion is a vertical or horizontal partition that divides units within a window or door frame. Its prime purpose is to give structural support and add more visual appeal to the installation.

Types of Mullions You Should Know

• Fixed Mullions: These are a permanent fixture in the frame and they provide stability for splitting multiple door or window parts.
• Removable Mullions: Need extra space to move furniture or equipment? These mullions are strong but can be easily detached when required.
• Glass Mullions: Glass mullions provide modern and minimalist designs with structural capabilities.
• Reinforced Mullions: Strong enough to withstand heavy applications, these are ideal for commercial environments demanding robustness.

Design Considerations

• Wood: Classic and timeless for traditional aesthetics.
• Aluminum: Lightweight and strong, ideal for commercial projects.
• Glass: Perfect for getting that ultra-modern and minimalist vibe.

Mullions vs. Muntins

• Mullions: These are structural elements that divide larger sections.
• Muntins: Decorative bars that separate individual panes of glass. Stylish, yes, but not built for strength.

Learn more about the difference between mullions and muntins here.

Since our founding in 1991, Panda Windows & Doors has specialized in state-of-the-art custom glass wall systems for both residential and commercial spaces. Operating from our manufacturing facility in Las Vegas, Nevada, we have been at the forefront of innovation for over 30 years. Our product offerings, which include over 80 high-end options, such as pivot doors, French doors, folding doors, lift & slides, multi-slides, horizontal sliding walls, and operable windows, are available in a range of materials, including aluminum, steel, stainless steel, bronze, solid wood, and aluminum-wood clad.

Panda Windows & Doors is widely recognized for its award-winning designs, engineering solutions, and rapid delivery times. We ensure that our customers throughout the U.S. and Caribbean receive their products within 6-10 weeks. Our company is trusted by leading architectural firms and glaziers nationwide, and we stand as the premier manufacturer of custom luxury windows and doors in the United States.

Learn About Custom Solutions from Panda Windows & Doors Today

Structural Functions Of Mullions

1. Weight Distribution

Mullions are used to evenly distribute the load of the big glass units across the frame, thus none of the individual parts is subjected to crushing load.

This is a huge issue in skyscrapers or expansive façades, where high wind loads and environmental stress are an ongoing threat.

2. Stability and Support

They make sure that glazing elements are fixed in a way that prevents them from drooping or moving. In complex curtain wall systems, mullions carry the load of the glass and other components to keep the whole assembly intact - even under heavy loads

3. Load Transfer

In tall buildings, mullions act like vertical channels, transferring weight from the roof and upper floors down to the foundation. This load-sharing ability is essential for stability, particularly for high-rise structures exposed to large wind pressures and adverse environmental loads.

4. Wind Load Resistance

Mullions prevent the windows from warping or from breaking in the case of storms and high winds, and therefore they are an absolute necessity in coastal or storm-prone areas.

5. Thermal Performance

Beyond strength, mullions also help with energy efficiency. Important thermal breaks are commonly found in contemporary designs that limit heat transfer for consistent indoor temperatures and reduced energy bills.

6. Enable Larger Openings

Want floor-to-ceiling windows or sweeping glass walls? Mullions make it possible! By providing the necessary support, they allow architects to design larger openings for stunning views and more natural light - without sacrificing stability or safety.

Read More: Parts of a Window: Names & Diagrams

Choose Panda Windows & Doors For Your Custom Designs

We have been serving across the US with top-quality doors and windows since 1991.

At Panda Windows & Doors, we're dedicated to bringing your custom design visions to life. Here's why partnering with us is a smart choice:

1. Our Philosophy: We focus exclusively on crafting luxury windows and doors customized as per your residential or commercial needs. Plus, our commitment to delivering premium-grade products means you receive the best solution always.
2. Research & Development: Our in-house engineering team is passionate about designing and developing products that meet your requirements. We use cutting-edge modeling software to perform wind, thermal, and structural analysis so your project is both functional and durable.
3. Materials & Sustainability: We prioritize sustainability by using materials like aluminum, steel, stainless steel, architectural bronze, and wood, all known for their recyclability. Our aluminum extrusions, for instance, are made of 70-75% recycled content. Additionally, we source premium hardware from top manufacturers worldwide for longevity in every product.
4. Testing & Performance: Nearly all our products are independently certified by the NFRC and AAMA, reflecting our commitment to quality and performance. With features like thermally broken designs and high-performance drainage sills, our products enhance energy efficiency and security.
5. Design Capabilities: We provide a diverse range of products, including sliding, folding, stacking, swinging, and pivoting options, all customizable to fit your project's aesthetic and functional needs.

Reach out to us to learn more about our products and get a free quote.

Frequently Asked Questions (FAQs)

Are mullions only used in windows?

No, while mullions are commonly found in windows, they are also used in doors, screens, curtain walls, and storefronts. They serve both functional and decorative purposes.

How do mullions affect energy efficiency?

Mullions can significantly impact energy efficiency by influencing the insulation properties and air leakage of windows and doors.

What maintenance is required for mullions?

Maintenance depends on the material used:

• Wooden Mullions: Should be regularly sealed or painted to protect against moisture.
• Metal Mullions (Aluminum/Steel): Require periodic cleaning and inspection for wear or damage.
• PVC Mullions: Generally low maintenance but should be checked for cracks or discoloration over time.

Can mullions be customized?

Yes, mullions can be customized in terms of material, profile, and finish to match various architectural styles.

What types of products do you provide?

We have a wide range of doors and windows, including:

1. Folding Doors

2. Lift & Slide Doors

3. Horizontal Sliding Wall Systems

4. Pivot & French Doors

5. Multi-Slide Doors

6. Retractable Screens

7. Architectural Windows