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What Is a Mulled Window?

What Is a Mulled Window?

Whether you’re building a brand-new home or renovating an existing one, deciding on the number of windows and their placement is trickier than it seems. Is it better to have three windows or one large window?

But what if you already have two or three windows on a wall and you want a single window instead? Can two or three windows be converted into a single window?

A mulled window is a large window that was originally two separate windows. It is better to mull two small windows into one large window. You cannot mull two large windows into one oversized window, as it would ruin the wooden frame for that wall.

Mulling a window is not a DIY project. It is a professional job that requires a contractor and maybe even a permit. If the frame of the wall cannot support a single window, then the contractor cannot mull the windows together.

How Are Windows Mulled Together?

There is no one easy guide to read and learn how to mull every type of window. Each window style and material are different and will require different methods.

To mull two windows together, the windows must be removed from the window frame and placed side by side together on a large work surface.

First, the nail fins must be removed. Then, line up the inner jamb edges of each window alongside each other and apply a silicone bead to those edges.

Then, press a mulling cap into the groove on the frames. After the mulling cap is secured, add another bead of silicone and press the windows together.

If the process is working, then the window should be perfectly aligned. After placing the mailing cap into the face groove, clamp the windows tightly together.

The contractor can attach the mull plates to both the bottom and top of the window frame. These plates need to cover the seam where both the windows join. Every type of window will require a different type of mull plate.

You can attach the mow plate to the window frame either by screwing in the plate or stapling the plate.

Now, it is time to attach the mull cover. Place it on the bottom of the window and allow it to slide up and around the window’s frame. It must be secured in place by tapping it firmly into the grooves of the frame.

Can All Windows Be Mulled?

Only a few windows can be mulled together. There are specific types of windows that can be mulled.

First, windows cannot be mulled together if the resulting window is extremely large and heavy, as the structure of the home wouldn’t be able to hold it upright effectively.

Can All Windows Be Mulled

Glass is extremely heavy, so the added weight of a large window can damage the structure of the wall.

The only way a contractor can properly mull two medium-sized windows into one massive window is to knock out the wall completely and build a different wall that can support the weight of the oversized window.

Also, windows that would combine and more at the corner cannot be mulled together. These are also known as wraparound windows.

If the windows going to be mulled are on the second floor, then it will not be possible to mull them. It is difficult enough to mull windows on the first floor. 

Mulling windows on the second floor causes additional issues. Second-floor windows are supposed to be smaller than first-floor windows, so that the second-floor windows are not too heavy for the walls and frame.

Are Mulled Windows Strong?

The strength of a mulled window greatly depends on how the contractor creates the support around the window. This is why it is so important to find a contractor that has performed window mulling before.

If your contractor has never mulled windows before, do not hire them. Mulling a window is not a simple job, even for a contractor. If done incorrectly, the wall cannot hold up the larger window.

In just a few months, the window frame could collapse and the supports for that wall could collapse as well.

Do Mulled Windows Open?

A properly mulled window should be able to open and close like any other window. There are some windows that are not designed to open, but those designs are not used for residential buildings like homes.

Windows that are not designed to be opened are more for industrial and commercial buildings.

Benefits of Mulling Windows

One major benefit for mulling two windows together is the increased amount of natural sunlight. Combining two medium size windows into one large window will improve the amount of sunlight that reaches into the room.

Studies have shown that exposure to natural light is better for human sleeping patterns, mood, and overall sense of well-being.

Benefits of Mulling Windows

Another reason to mull two windows together is to improve the atmosphere of the room. Having two windows can make a room seem cramped.

You’d be surprised at how much the feel of a room improves when there is one large window instead of two small windows. The natural sunlight that illuminates the room will make the space seem larger.

A third reason to mull two windows is to improve the amount of airflow in a room. In fact, mulling to windows together can improve the airflow of not just that room, but the hallway and even any rooms besides the main room.

Are Mulled Windows Expensive?

When two fixtures are combined into one fixture, the resulting fixture usually costs less. But, with mulled windows, they usually cost more.

That is because the mulled window and the wall frame require work. More material and a stronger window frame are needed.

Can a Contractor Remove a Window?

So, you’ve consulted the contractor doing the renovations to your home, and they have told you it will not be possible for them to mull two or three of your dining room’s windows into a single window.

Well, if you cannot transform three small windows into one oversized window, can you at least remove a single window? Can you remove the middle window and keep the two remaining windows?

It is possible to remove a single window and install a larger window. The contractor will have to alter the wooden frame so it can support two windows instead of three windows.

The remaining windows will not reach each other. But two wide windows will allow more air and light inside and make the room look more spacious.

Also, the contractor may remove two of the three windows from the left and right side and then widen the remaining middle window.

Conclusion to Mulled Windows

A mulled window is a single large window unit that was once two separate window units. Not all windows can be mulled together. Mulling a window requires altering the wooden frame inside the wall.

If a window mulling is done incorrectly, the wooden frame will not be able to support the heavy window and it will collapse.

Lindsay Reed

Hi, I'm the founder of! I created this website to be a resource for everyone who wants to make the best home possible.