Bay Windows: Outdated and Expensive or a Good Investment? [Solved]

By thewriteDuffy •  Updated: 06/07/24 •  8 min read

Bay windows not only bring charming architectural character to the exterior of a property, but they also add space and light to the interior too. 

In this article, we’re going to take a close look at what is considered a bay window, how they differ from bow windows and also dive into the cost and special construction needs of bay windows so you can decide if they would be a good investment for your home, or if you should consider different options.

What are Bay Windows?

Bay windows are a set of windows that create an alcove, which protrudes away from a building.  Usually, this set consists of three or more windows, which are arranged in a box, hexagon, or octagon shape.

A modern bay window typically has a fixed middle window, such as a picture window, with side windows that open. Casement or double-hung windows are usually used for these opening side windows. 

Are Bay Windows Out Of Style or Outdated?

Bay windows date back to medieval times and were an important architectural feature in these dark, gloomy homes.  When looking at historical architecture, we see bay windows in properties from the 1400s, their popularity really spiked during the English Renaissance period.

So, are bay windows considered outdated? Not at all! While bay windows have experienced a lull in popularity over the last couple of decades, it’s once again becoming common for developers to include bay windows in their new builds. 

Bay windows continue to cycle back into popularity because of the added curb appeal they can bring to a home. The modern buyer also loves the light and ventilation offered by bay windows, not to mention the additional space that allows for a peaceful window seat or the placement of a small table and chairs. 

A lot of the reason why bay windows were out of vogue until recently is because of their lines. Being such a traditional style of window, they’ve seemed out of place in the sleek lines of many modern styles of the last few decades.  But plenty of home buyers today now yearn for a bit of character, and a bay window offers plenty of it.

Bay windows add interest to flat exterior facades and character and versatility of use to the interior. With a choice of shapes and styles available, bay windows can be chosen to suit a range of modern properties. 

Bow Windows vs. Bay Windows: What’s the Difference?

Both bow and bay windows protrude from the wall, but while bow windows are composed of four or five window panels fitted at  90, 130, or 150° angles to create a curve, bay windows tend to be three window panels arranged in a rectangular, hexagonal or octagonal fashion. 

Further, bow window panels tend to all be the same size, while in bay windows, the center panel is usually larger than the other two, and is often installed as a picture window.

Light Difference Between Bay Windows and Bow Windows

Although a bay window may have one larger panel, it’s actually the bow window that allows most light into a room, due to the greater number of panels used and the curved nature of this window.

Construction Difference Between Bay Windows and Bow Windows

Thanks to their curve, bow windows can be used on the corner of a building and therefore installed in the right corner, you can end up with an impressive panoramic view.  Bay windows on the other hand cannot be fitted into a corner, only into an external wall.  Bay windows offer more internal space than bow windows and yet they often cost a little less to buy.

If you’d like more information about bow windows, click here.

Why Do They Call It a Bay Window?

There are a couple of proposed origins of the term “bay window”. It has been suggested the name comes from the old French word “baee”, meaning an opening. It may also be called a bay window simply because it creates a bay-like shape on a house plan.

The two potential origins both refer to the characteristically unique physical structure of the window. 

This “bay” requires some additional building work because the window panels don’t sit flush in the external wall. Rather, they require a supporting sill-height wall, constructed to fit the shape of the chosen bay. Generally speaking, the bay is created by setting the windows at inside angles are 90 degrees or 135 degrees, though triangular bays formed by two windows set at 120 degrees are often found – called Oriel bay windows.

Do You Need to Build a Foundation for A Bay Window?

Building a foundation is one way to safely install and stabilize a bay window. Building a foundation is the best choice if your bay window is going to sit flush to the ground, rather than protruding out further up the external wall.

The foundation for a bay window needs to be deep enough to prevent issues over time such as movement, heat loss, and damage to the external wall. 

With that said, you may also be able to support the weight of a bay window via cantilevers, whereby supporting joists or cables help to suspend the window.  This method is naturally utilized when you’re installing bay windows on an upper floor, but you can use this approach at ground level too if your local codes permit it. 

Always consult your local building codes when deciding on a bay window and note that the foundation for a bay window may be referred to as “footings” in the building regulations. 

In general, you’re likely to need to excavate to a minimum depth of 1 meter, with 600mm of concrete and 450 mm of clockwork, but again, this varies by location.

Do You Need Planning Permission for A Bay Window?

If you’re just replacing an existing bay window, you’re unlikely to need a building permit. If you’re installing bay windows for the first time to the front of a home, you’ll most likely need to apply for building permission because you’re increasing the proportions of your home and altering the appearance of the frontage.

The process of applying will help you access all the required building regulations, and this can be really useful if you plan to install the window yourself.  If the time and expense involved with a planning application are putting you off, it may help you to know that bow windows generally don’t require a permit. 

If you plan to install new bay windows (to replace another style of window) at the side or to the rear of your home, it is less likely that a planning permit will be necessary.  But this depends on the location of your property sides and rear in relation to the boundaries of your home and to the street or government-owned land.

What Is the Average Cost of A Bay Window?

Because of all the building concerns, bay windows are more costly than flat window styles. When you omit bay windows from a house plan, you can reduce the need for bricklaying and masonry.  Timber frames (which you can use if other styles of window are being installed) are quicker and therefore less expensive to construct.

An average-sized, three-pane bay window will cost between $1,500 and $3,500, before installation. Installing this type of window takes more time and work than other flat styles of windows. You can expect a minimum of $400 fitting costs to do a straight replacement bay window and more to install one from scratch.

As with all window styles, high-quality models can cost a lot more, while budget options are available.  In terms of energy efficiency, appearance, and durability, opting for the highest quality bay window you can afford is wise, especially in terms of adding value to your home.

Something important to keep in mind when it comes to purchasing a bay window is that the above costs don’t take into account the cost of amending the external wall if it is currently flat.


If you’re keen to increase the proportions of a room, welcome in extra natural light, and improve the curb appeal of your property, then the traditional bay window is a superb choice for you.

Though applying for a building permit may be a bit of a chore, just think about the end product – the elegant window seat and the enhanced view! 

If you’re still not sure if bay windows are right for your space, click here to see our list of the 13 most popular window styles for your home.


At home, April is a mom, wife, and DIY darling. Among other home projects, she helped her husband Dan renovate their 1986 bungalow and is currently designing and decorating the 2023 custom home they are building themselves. Professionally, April is a writer, author, and online marketer with 15 years of experience writing for newspapers and magazines, building online authority websites, and publishing books.