Different window styles can change both the appearance of a property and the way each room works. Casement, flush, sliding sash, bay and bow windows all have different characteristics, and the right choice is not always the same throughout an entire home.
This guide compares the main window styles available, where they tend to work well and what to consider when choosing between them.
The style of a window affects far more than how it looks from outside.
It determines how the window opens, how much ventilation it can provide, the amount of visible frame, how easy it is to reach and operate, and how well the finished installation sits with the character of the property.
For that reason, choosing a window style is usually easier once you have already thought about what you want the replacement windows to improve. If you have not done that yet, start with our Choosing the Right Windows guide.
The aim is not necessarily to find one style and use it everywhere. Different rooms can have different practical requirements, although the exterior of the property should still feel considered as a whole.
Casement windows are one of the most familiar window styles used in UK homes.
They are hinged rather than sliding and can be configured in numerous ways, with different combinations of fixed panes and opening sections. This flexibility is one reason they work across such a broad range of properties.
Casement windows can suit traditional, transitional and modern homes depending on the frame system, colour and configuration selected.
They are particularly useful where flexibility is important because the arrangement of opening sections can be adapted around the room and the proportions of the existing opening.
They can also be a sensible option when replacing conventional windows without wanting to significantly change the architectural character of the property.
Standard casement windows normally have an opening sash that sits slightly proud of the outer frame when closed.
That creates a different external appearance to a flush window, where the sash sits level with the frame.
Neither is inherently better. The distinction is largely about appearance, detailing and which system suits the property.
Explore: Casement Windows
Flush windows are designed so the opening sash sits level with the outer frame when the window is closed.
That relatively small construction difference can noticeably change the appearance of the finished window.
The result is a flatter, cleaner exterior with less obvious overlap between the opening sash and surrounding frame.
Flush designs are frequently considered for traditional homes, stone properties and cottages because their flatter appearance can sit comfortably with simpler architectural detailing.
They are not restricted to period properties, though.
The same clean lines can work extremely well on contemporary homes where the aim is to create a restrained, uncluttered elevation.
Colour, glazing bars, frame proportions and the surrounding architecture make a considerable difference to the final effect.
This is worth stressing because flush windows are sometimes marketed almost exclusively as a heritage product.
A traditional-looking flush window and a contemporary flush installation can use the same basic principle but look very different once colour, hardware and configuration are taken into account.
If you are choosing between a flush and conventional casement design, consider the property first rather than assuming one belongs to old homes and the other to new ones.
Explore: Flush Windows
Sliding sash windows operate very differently to casement windows.
Rather than opening outward on hinges, one or more sashes move vertically within the frame.
Their proportions and method of opening are strongly associated with Georgian, Victorian and Edwardian architecture, which makes them particularly important where the character of an older property is being retained or restored.
For the right property, a sash window can look considerably more appropriate than inserting a conventional outward-opening casement into the same opening.
Modern sliding sash systems can reproduce much of the familiar appearance while incorporating contemporary glazing, security and operating mechanisms.
They can also work where outward-opening windows would be inconvenient.
With sash windows, the details matter.
The relationship between the upper and lower sash, glazing bars, frame width and the position of the window within the opening can all affect whether the finished result looks convincing.
This is particularly important on older elevations where windows form a strong part of the original architectural rhythm.
If heritage considerations apply to the property, read our Planning & Conservation guide before committing to major changes.
Explore: Sliding Sash Windows
Timber alternative windows are less about one particular method of opening and more about recreating the appearance associated with traditional timber windows using modern window systems.
They are worth considering where the look and detailing of conventional uPVC does not feel right for the property, but the ongoing maintenance associated with painted timber is undesirable.
Character properties, cottages, converted rural buildings and period-style renovations are obvious candidates.
They can also suit newer homes deliberately designed with traditional architectural features.
The important distinction is that "timber alternative" should not be treated as a guarantee that any particular product will suit every old property.
Frame proportions, joints, colour, hardware and glazing details still need to work with the building.
If you are comparing this type of system with aluminium or more conventional uPVC, the Window Materials guide is the better place to examine the differences.
Explore: Timber Alternative Windows
Bay and bow windows are different from most of the styles in this guide because they affect the shape and character of the property as well as the individual window units.
Both project outward from the main elevation, but they do so differently.
A bay window typically uses a more angular arrangement, commonly with a larger central section and angled side windows.
This can create a defined projection and additional usable space inside the room.
Bay windows are a familiar feature on many Victorian, Edwardian and later properties.
Bow windows normally use a greater number of window sections arranged to create a gentler curve.
The result is generally softer externally and can provide a broad outlook from inside.
Where an existing bay or bow is being replaced, preserving the established proportions of the property will often be an important consideration.
Creating a completely new projection is a different type of project and may involve structural and planning considerations beyond simply selecting the window units.
Both options can introduce light from multiple directions and create a strong visual feature, but their shape, width and relationship with the rest of the elevation are noticeably different.
Explore: Bay & Bow Windows
Aluminium windows are included here because the material can have a major influence on the style and proportions of a window.
The strength of aluminium can allow comparatively slim-looking frame sections, making it particularly appealing where larger areas of glazing or a more contemporary appearance are wanted.
Modern homes, extensions and properties with larger glazed openings are natural applications.
Aluminium can also be used successfully alongside more traditional architecture where the intention is to create a deliberate contrast between old and new.
It should not automatically be dismissed for an older property simply because the material feels contemporary.
The question is whether the finished design works with the architecture.
For a more detailed comparison between aluminium, uPVC and timber alternative systems, continue to the Window Materials guide.
Explore: Aluminium Windows
Secondary glazing takes a different approach entirely.
Instead of removing the existing external window, a second glazed system is installed internally.
That means it is not really a replacement window style in the conventional sense, but it belongs in the buying decision because there are circumstances where retaining the original window is preferable or necessary.
It may be considered where original windows contribute significantly to the character of the property, where restrictions make conventional replacement difficult, or where additional thermal or acoustic improvement is wanted without removing the existing external windows.
Whether it is appropriate depends heavily on the property and what you are trying to achieve.
Listed buildings and conservation situations require particular care, so do not assume that secondary glazing automatically avoids every consent issue.
Explore: Secondary Glazing
Yes, but it needs some thought.
Different rooms often have different practical requirements, and certain parts of a property may have been built at different times. An extension, for example, does not necessarily need to reproduce every detail of the original house.
The risk comes from treating each window independently and ending up with an elevation that feels disconnected.
Try to maintain a common visual language through elements such as colour, frame proportions, glazing lines and hardware even when opening styles vary.
A contemporary extension attached to a traditional property might deliberately use aluminium glazing while the original part of the house retains flush or sash-style windows. Done intentionally, that contrast can work extremely well.
There is no universal rule here. Context matters.
Older properties deserve more than a blanket recommendation.
A Victorian terrace might originally have used sliding sash windows. A rural stone cottage may suit a flush or timber alternative system. Another older home may have undergone substantial alterations over the decades and no longer have one obvious historic specification to reproduce.
Before choosing, look at:
Our Planning & Conservation guide covers the regulatory side, while Window Colours & Finishes looks more closely at the visual choices.
Modern properties often provide greater freedom, but that does not mean every contemporary home needs huge panes of aluminium-framed glass.
Casement windows remain a practical choice. Flush windows can create cleaner external lines, while aluminium windows are worth considering where slimmer-looking frames and larger glazed areas are priorities.
The architecture should guide the decision.
Look at the shape of the openings, roof lines, doors, exterior materials and the amount of glazing already present before deciding how visually prominent the new frames should be.
No.
Fixed panes can sometimes provide a cleaner appearance and a larger uninterrupted glazed area where an opening window is not needed.
However, ventilation, access, cleaning, fire safety and Building Regulations can affect what is appropriate in particular locations.
This is why window configurations should be planned room by room rather than simply making every pane fixed to maximise glass or every pane opening "just in case".
The Choosing the Right Windows guide covers this broader decision-making process.
A showroom sample is useful for understanding construction, finish and hardware, but it does not show how that window will look across the entire front of a house.
Try to consider the finished elevation.
A frame that appears fairly substantial when viewed as a small corner sample may look perfectly proportioned within a large opening. Conversely, details that seem insignificant in isolation can become very noticeable when repeated across ten or fifteen windows.
Completed projects can therefore be as useful as product samples when narrowing down your choice.
If possible, look at examples installed on properties with some similarity to your own.
If you are struggling to decide, start with three questions.
First remove anything that clearly works against the character or proportions of the property.
Think about ventilation, furniture, access, cleaning and how the room is used.
Once the practical requirements are covered, this matters.
You will be looking at the windows every day for years. There is nothing wrong with choosing between two technically suitable options because you simply prefer the appearance of one.
At that point, material, glazing, colour, security and cost help refine the specification rather than deciding the basic style.
If you have narrowed down the style but are unsure which frame system makes sense, continue to the Window Materials guide.
You can also explore the rest of the Windows Buying Guide:
Or explore the individual window ranges directly:
