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Double Glazed Bay Windows: A Complete Guide of Costs, Benefits & Features

If your home already has bay windows or you’re thinking of swapping your flat windows for double glazed bay windows, you’ve come to the right place. Here, we’ll give you the low down on the perfect bay window style and what you can expect from bay double glazed windows. First of all, let’s look into the history of these beautiful window units.

Bay window origins

Bay windows are windows that project outwards from a property. Inside the property, they create a recess, which is the ‘bay’.

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Apparently, the term ‘bay window’ originates from Middle English, where it was baywyndow or baywyndowe. Before that, the word ‘bay’ (that denotes an opening in a wall), is believed to come from the Old French word baee, which meant hole, opening, or gulf.

Bay windows first started appearing during the English Renaissance era – between the end of the 15th century and the beginning of the 17th century. They were usually found in mansions or other grand houses.

Renaissance bay windows usually extended outwards from the wall with nothing underneath them touching the floor.

During the Gothic time, bay windows were commonly found in churches and chapels and people would use them for private worship.

In Victorian times, they became a common sight on all homes – including on upper floors.

Double Glazed Bay Windows

Bay windows today

Nowadays, bay windows are seen on all sorts of properties, both old and new. They’re often added for their panoramic views and to create additional internal space in the room.

Bay windows are such a popular feature these days that many people are getting a new bay window to replace their existing flat window styles. More and more, people are appreciating how windows serve much more of a purpose than just letting light in.

Let’s take a look at the key details of bay windows.

Key features of bay windows

Bay windows usually have three or more panes of glass to create their shape. Common inside angles range from 90 degrees (box bay windows) to 150 degrees. They can be fitted with decorative glazing options and multipoint locking on individual window units.

In terms of bay window design, here are the most common bay window styles:

Free-Standing Bay Windows

A free-standing bay window would be fitted to an existing window aperture. The bay would be the same height and width as the current window opening. Essentially, you’re replacing the flat casement windows with a more 3D-effect window. These are often called bow windows.

Integral Bay windows

An integral bay window means that the bay is a part of the interior and goes from floor to ceiling. These bay windows might even extend to the full house height up to the roof. Lots of bay-fronted period homes are designed like this.

Boxed Bay Windows

As their name suggests, these are rectangular with a flat front and flat sides. These are common in Europe. They can also be called ‘canted windows’. Many people consider this to be the real deal of bay windows because of the three-sided configuration.

Bow windows

This type of bay window was most popular in England in the 18th century – though you wouldn’t find a uPVC bow back then! Bow windows are curved and there are usually four to five panes to create the effect.

Circle bay windows

These are not too dissimilar from bow windows. These look like a semi-circle and they are often made with decorative glass.

Double Glazed Bay Window Functionality

The way your bay windows function depends on the chosen style. Most bay windows incorporate casement windows but you can see sash windows in bays too. In fact, a lot of period properties have sash windows in the bay.

For anyone who doesn’t know the difference, a casement window opens outwards from a side hinge on the window frame. A sash window, on the other hand, slides up and down within the window frame. Both window designs can incorporate double glazing.

It’s also possible to find awning casement windows, for anyone who prefers a window that opens at the bottom.

Alternatively, you don’t need opening windows at all. It’s perfectly acceptable to have fixed windows too.

Double glazed bay window advantages

We’ve already alluded to the fact that bay windows allow more natural light and more space in the interior. Let’s look at some of the advantages in more detail.


Firstly, with a window that extends outwards, you get a better view of the outside. If you install a bay window in an upstairs room, you can create fantastic panoramic views. After Covid-19 pushed a lot of people to spend more time indoors than ever before, lots of people are looking at how to create better views.

Increased space

If you have a floor-to-ceiling bay window, you’ve potentially gained a lot more room in your interior. Many people use these spaces as a seating area, a storage area, or for setting up a toy area for their children. It’s also a great place to have a bookshelf and coffee table.

Low Maintenance

If you’re replacing old windows (especially wood frames), you’ll soon come to realize just how low maintenance a uPVC bay window with double glazing is!

Once installed, you can enjoy many years in the extra space and more light you’ve created, without worrying about having to make further home improvements in the near future.

Increased security

New windows will always be more secure than the ones they’re replacing. These days, new bay windows are designed to deter would-be intruders from even attempting a break-in. What’s more, if you install laminated or acoustic glass, the panes will be really difficult to break!

Material options

When it comes to choosing material options, you’re spoilt for choice. Most people chose uPVC bay windows as these are easily available and usually offer the most competitive price. As well as uPVC windows, you can choose aluminium or timber frames.

If you want to have something a little different, nowadays uPVC windows come in a range of colours. You can even choose a different colour for the exterior and the interior. There are neutral colours, wood-like colours, or bold colours to suit a particularly eccentric property. You can even get doors to match.

Glazing options

Bay windows come with a range of glazing choices. You can go for simple double glazing or choose different glass designs like leaded glass, laminated glass, obscure glass, impact glass, or tempered glass.

As well as this, you have choices to install things like Georgian bars and leaded windows or have different patterns like diamond or colonial.

Double glazed bay windows disadvantages

It’s important to discuss the disadvantages of bay windows as well as the advantages.

Installing new windows (no previous bay)

The most common problem is installing one from scratch if you haven’t already got one in place. Not only will these bay windows cost more, but they will also be more time-consuming to fit.

If you don’t already have a bay window installed, you might also have to get planning permission, which is worth considering.

Good quality comes with a cost

When considering double-glazed bay windows, you want them to last. Often, the cheapest, low-budget window designs will not last as long. You might find them distorting, creaking, or even leaking over time.

Good quality bay windows are expensive compared to other window designs so it’s worth working out what you can afford before getting quotations.

Besides the windows themselves, you might want to consider getting the walls below checked for structural problems before spending such a large outgoing on new windows.

You can get bay windows fitted with structural bay poles that increase their structural integrity.

More light and extra space = more heating

It’s great to create extra space in your interior but you should also be aware that this is more space to heat in winter. What’s more, with more glass, you will also lose more heat through the windows too.

If you’re replacing very old windows, you probably won’t notice any difference, however. The chances are cold air was getting in through small cracks that will disappear with your new windows! New bay window designs are planned with energy efficiency in mind!

Bay Windows Installation Cost

Many people often want to know how much bay windows cost? This is really difficult to answer as all designs and requirements will come with a different price tag.

In terms of materials, uPVC bay windows are most likely to cost less. A uPVC bay window is pretty standard and so there is lots of competition out there and you might be able to secure a price promise for a good deal.

You’ll pay more for timer frames and for aluminium frames. You’ll also pay more for a bow window because they have more panels and separate glass frames.

As for glazing, you’ll pay standard prices for double glazing but you can expect to pay more for specialist glazing options like soundproof glass, for example.

The cost will also rise depending on how the windows work. Fixed panes will be cheaper than casement or sash windows as these need hardware for their different turn styles.

Final thoughts on double glazed bay windows

If you’re just starting to think about a new double glazed bay window, you’ve got a lot of decisions to make. If you’re replacing like for like, things will be much more simple!

However, if you’re replacing a flat window with a bay window, here is a summary of things you need to consider:

  1. The structure of the window (bow window, bow and bay windows, etc.)
  2. The window designs (casement or sash, for example)
  3. The frame material (a uPVC bay window might be a good idea if you already have uPVC French doors, for instance)
  4. The glazing type (double, acoustic, secondary glazing, etc.)
  5. The colour (both the interior and the exterior can be chosen separately with uPVC bay windows). Also, consider whether you want them to match the external doors.

All in all, if you do go for bay windows, you’re guaranteed to have more natural light and more space in your room. Installing new windows is a great start to making home improvements and will make such a difference to the appearance of your home both inside and out.

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Bay Window FAQs

What are bow bay windows?

Bow windows are rounder in appearance. Because of this, a bow window will have more panels and panes of glass.

What is the difference between bow and bay windows?

Bow windows are often called bow bay windows because they’re very similar. Essentially, the difference between bow and bay windows is that a bow window has more panels and windows to create a rounder look both inside and out.

Can you get uPVC bay and bow windows?

Yes. Both bow and bay windows are available in uPVC. A uPVC bow window will be more expensive than a bay window – but cheaper than the same in wood or aluminium.

Is a wooden frame bow window expensive?

If you’re keen on wood, both bow and bay windows in wood are more expensive than their uPVC counterparts. The cost, however, depends entirely on the design and the type of glass used. It’s worth getting quotations from a number of sources to compare.

How can I guarantee my bow and bay windows are good quality?

Provided you use a reputable company that is a member of the glass and glazing federation, a bow and bay window will likely have a guarantee for a number of years. It’s worth asking window companies about the guarantees they have on their bow and bay windows.

Compare Window Costs Online

You can save up to 65% OFF new windows and doors by using our online cost calculator.

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Receive as many as 4 quotes
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