Among South East homeowners, two of the most popular window styles are casement and flush casement. However, many people are uncertain exactly what the difference is between the two. They’re both ‘casement’, so surely they’re the same? This is true to a certain extent; both types are window sashes that open on hinges at the side.

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What is the difference between flush and casement windows?

Casement Windows Flush casement windows
Lipped frames Flush frames
Traditional appearance Modern appearance
Also referred to as ‘stormproof’ Weather resistant
Energy efficient Energy efficient
Available in a range of colours and finishes Available in a range of colours and finishes


The key difference between casement and flush windows is that a regular casement window is ‘lipped’, with the openable parts protruding from the frame, while a flush casement window lies flat against the wall.

Here is a casement window:

white casement window
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And here is a flush casement window:

flush sash window

As you can see, with the casement window, the frame stretches past the glass. In the flush casement, meanwhile, the glass lies level, or ‘flush’, with the frame.

Should I choose casement windows or flush casement windows?

Both styles of window make a fantastic addition to any South East home. The versatility of a casement window is one of the main reasons why it’s the most popular style, not just in Greater London, but across the whole of the UK.

The lipped design of the standard casement window is arguably better suited to older homes that are looking to preserve their traditional aesthetic. This is especially the case if you were to add decorative glazing bars to the window panes, as pictured below. This is particularly compatible with Victorian or Georgian properties.

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white casement windows

The sleek and supple style of flush casement, or flush sash windows, are better suited to more modern properties. Modern home exterior trends are all about minimalism and elegance, which is exactly what you get when you opt for flush casement windows. The style is particularly compatible with darker colours like black and anthracite grey.

black flush sash window

Do flush casement windows leak?

Due to their lipped frames, regular casement windows are often also referred to as ‘stormproof’, as the frames help to divert rainwater away from the home. However, this does not mean that flush casement windows are not resistant to extreme weather. By contrast, they are just as resistant to the elements. Often, they are fitted with an additional exterior window sill, where water can trickle down to and be safely guided away from the property.

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Are flush casement windows any good?

Absolutely! As well as exhibiting stunning aesthetics, all our flush casement windows also demonstrate fantastic thermal properties. Compatible with high-quality double glazing technology, all our casement windows achieve incredibly low U-values. This means that they minimise the amount of thermal transfusion through the glass, helping the home to retain heat and reducing energy bills.

Whichever style you choose, both will do you immensely proud, increase your kerb appeal, and minimise your carbon footprint.

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brown flush sash window

Casement and flush sash windows in Slough, London, and across the South East

Unique Glazing are one of the leading installers of premium uPVC and aluminium casement windows in the Greater London area. For more information on how we can improve your home, or to get a project off the ground, please do not hesitate to contact us or get in touch for a free quote if you already have some ideas!

Delivering Customer Satisfaction

We strive to provide the best service for our customers. Here are some Checkatrade reviews from our happy customers.

High quality work and fittings

I would like to thank you for delivering high quality work. Guys are professional and very precise, quick and reliable. They will well prepare the place for the work and...

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August 2023

I would definitely recommend

Unique glazing carried out a double glazing window install required. It probably wasn’t the biggest job they’ve undertaken but the service and attention to detail was certainly of a what...

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September 2023

I will be using them again in the future

I had 9 windows fitted at my house yesterday - the two fitters were amazing. The workmanship was of a high level, left the house spotless before they had left....

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October 2023

Exceeded my expectations

From start to finish we had a pleasurable experience with Andy and his team. Andy came and answered all my questions and came back to my house many times to...

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October 2023

Immaculate service

The windows replacement service was perfect. All the windows were done and fitted within the time I expected. Thanks to the friendly staff for their absolutely immaculate and friendly service....

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October 2023

Great Windows and experience

We had the front windows and door replaced and the whole process was great. No pressure, emailed us a quote. The surveyor abs installers were very helpful and hardworking. Will...

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July 2023

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