Room With a View: Using Mulled Windows in Home Design

Picture this: Lush greenery as far as the eye can see, leaves gently wafting with the breeze, and the twittering of birds in the distance. Yet, you can’t feel goosebumps from the wind because you’re enjoying these views from behind the expansive mulled windows in your forest cabin.

Intrigued? Read on.

Mulled windows: The Outpost

In construction terms, window mulling is the process of joining two or more windows together by their frames, to create a larger and more dramatic glass area. No matter the size of your home, mulled windows are a great way for homeowners to get uninterrupted outdoor views and invite in natural light.

Eyes may be the windows to a human soul, but literal windows reflect your design aesthetic, improve your home’s look, and usher in light. So if you’re dreaming up a new home and need help designing window units, here’s what you need to know about mulled windows.

What Is Window Mulling and What Goes Into a New Mulled Unit?

Mulled windows: family bonding at their living room

As described above, window mulling combines two or more windows, or individual units, together by their frames to create a larger window. It’s for homeowners who want their houses to have a sleeker, chicer, and cleaner look. 

Mulled windows have window frames, window glass, mullions, and transoms. A mullion is the vertical beam that divides a window into smaller window glass units (mullions can be made from strips of material like wood, metal, or vinyl, placed in a grid formation.) They can be decorative or designed to provide support to the glazing, and are often added to give structural support to a window arch. A transom is a horizontal beam or structure that separates the top of a window or door from the wall above.

Since window mulling joins two windows, it can be applied to different types of windows, such as:

  • Single hung windows: They have a single operable lower sash
  • Double hung: Two operating sashes that move up and down, which provides ventilation at the top, bottom, or both
  • Casement windows: Attached with side-mounted hinges, and swing open from one side only

Ideally when joining two window units together, they should be of the same style.

Can All Windows Be Mulled?

If you want to add mulled windows to your new construction, think about this at the initial design stage and inform your architect and interior designers, so they can be built on-site.

Alternatively, in the case of a window replacement project or renovation, prefabricated mulled windows can be fitted in, or engage a contractor to combine two separate units and create a mulled window. An experienced professional can do this without damaging your structure’s integrity. Pro tip: Make sure to get a warranty if you’re opting for a pre-made set.

However, there are some factors to consider when it comes to window installation.

For one, not all windows can be mulled. Professionals will have to take the size of your window and glass into account, as home walls may not be able to support a mulled window if the combined units are too large or heavy. Secondly, you need to consider building codes and zone regulations when making any home improvements or building from scratch. It’s never a good idea to take rules lightly, in case you end up dealing with a Ron Swanson instead of a Leslie Knope.

Companies like DEN Outdoors that specialize in homes to shine in the outdoors tend to focus on mulled windows in their designs, with floor-to-ceiling window units often the focal point of the designs. Connect with us if you’re thinking of building a home, as we join you at the planning and ideating stage of the building process — and offer wallet-friendly packages to help you design your dream home.

All of our plans contain a precise “Window and Door Schedule” — simply put, it’s a list of all the windows and doors you’ll need to support the design.

Both Starter and Complete packages are available, with the former aimed at those in the research stage, and the latter offering more details (like a detailed budget, materials spreadsheet, labor connections, and more), but you can always apply the money spent on a Starter package toward a Complete package. The Starter is for commitment-shy Chandler Bings, and the Complete is for Ross Gellers who are all-in.

Benefits of Mulled Windows

Mulled windows: living room with leather couches

Here’s why bigger is better when it comes to new windows. While it’s true that typically, mulling windows together costs more than if you split them apart, the benefits outweigh this con in the long-term.

Natural light: The first and most obvious benefit of joining two window units is more natural light. This trick works especially well in spaces that are smaller and cramped. It helps create a better ambience too, especially if you’re looking out to gorgeous views.

Focal point: A large, spacious window becomes the scene-stealing factor of the space it sits in. Think of it as a painting with an ever-changing image as the seasons change.

Curb appeal: As the features of a house that make people stop and say “ooh” when seen from the street, enhanced curb appeal is always welcome. Mulled windows with a larger window frame tend to make your home look even more attractive.

Energy-efficient: Since the larger size of the windows means there’ll be a profusion of natural light, you’ll be able to save on electricity, making them an energy-efficient choice! Using insulated glass units will prevent heat loss through your windows. (Yes, this means less money spent on artificial heating, so win-win).

Window Mulling Inspiration

If you aren’t sure that having large, expansive windows for your home is the right way to go, have a look at the designs from DEN to convince you — across budgets, sizes, and interior styles.

Tiny House 2.0

Tiny House 2.0

Just because you have a compact home doesn’t mean you can’t have big windows — as seen in DEN’s 144-square-foot Tiny House 2.0. A full wall of windows in this sleek, minimalist design that sleeps two means you can make the most of natural light, while losing yourself in the beauty of the outdoors.

Modern Alpine Plus

Modern Alpine Plus

The curb appeal of this 816-square-foot, two-bed loft cabin from DEN is off the charts, thanks to an expansive front-facing facade of glass. Imbued with alpine aesthetics, the home is your answer to feeling like you’re one with the woods, without actually stepping outside.

A-Frame Family

A-Frame Family

A luxurious escape sitting at 2,146 sq. ft., the A-Frame Family from DEN is a stunning Scandinavian-inspired design with three bedrooms and two baths. The scene-stealers are the expansive, nearly floor-to-ceiling energy-efficient windows, which will inspire you to consider window mulling in your own home.

Get Started on Your Mulled Windows and More

Whether you’re a prospective homeowner or home builder considering mulled windows in a new design, or want to give them a shot as replacement windows in your home improvement endeavors, now you know more about how this feature can enhance your abode.

If you’re ready to start gazing into the outside world unencumbered, DEN's many house plans will help you customize the right home for you — windows and all. 



  • Wadding, J. (2023, January 31). Window Mulling 101: What it is and its benefits. ARCH Exteriors.
  • Wallender, L. (2023a, February 13). Pros and cons of popular window styles. The Spruce.
  • Geerts, S. (2023, April 12). 23 Ways to add curb appeal for the best front yard on the block. Better Homes & Gardens.