Aluminium flush casement windows are now firmly established in the UK market, with plenty of choice for homeowners and the trade. Flush casement windows differ from regular windows because the opening elements sit within the frame rather than overlapping it. The aesthetic advantage is balanced and symmetrical sightlines. Here is who makes the best aluminium flush casement window.
Why choose a flush casement window?
The concept of a flush casement window is not new. Original timber windows have featured a flush opening sash for many decades. PVCu systems followed with Evolution Windows, being the first to introduce flush timber-look or timber-alternative windows.
Aluminium as a flush casement has been a little more challenging to create, because of how aluminium is extruded and how windows and mechanically joined at the corners.
Now you have a great choice of contemporary or traditional flush casement windows in aluminium.
The best flush casement aluminium window – Alitherm 400.
The Smart Systems Alitherm 400 is a versatile window range, and its flush casement version, we think, is arguably the best on the market right now. As well as a flush casement option, it’s also available in a steel-look, flush steel look, tilt and turn, and fixed windows, making this a complete product for your home.
Alongside its multiple design options, the hidden trickle vent is a fantastic feature. U-Values can be unclear, so it’s important to check specifications carefully. This is flush outside only and stepped inside.
Reason to buy: We regard Alitherm 400 as the best overall flush casement window because it provides the best balance of styling, quality and price. The other window options and matching Alitherm 400 door suite also add to its appeal.
Cortizo Casement Windows
Newer in the market, Cortizo Casement Windows are designed specifically for the UK market, and in our view, they offer one of the slimmest and most contemporary casement profiles available today. The flush casement version in particular provides a clean and well-proportioned look that competes directly with the best-known British and European systems.
Flush externally and stepped internally, these outward-opening windows have a great look and feel to them, and are suitable for replacement and new build projects. You can also use these in commercial buildings.
Reason to buy: Cortizo are the best aluminium flush casement windows with contemporary styling. Elegant, appealing, and with impressive size capability. Cortizo windows are a serious and possibly better alternative to more widely known UK brands like Origin, and certainly cheaper.
Schüco AWS 80 Windows
Unlike the UK, when houses are on the sales market in Europe, the brand of windows and doors fitted is part of their marketing. Enter the premium, gorgeous and elegant Schüco AWS 80, another contender if you’re looking for the best flush casement aluminium window.
The Schüco AWS 80 SC is one of the most advanced aluminium casement windows currently available. It really does set a high performance benchmark, and as is the premium window brand. Schüco has designed this for the UK market, and it is a future-proofed window.
Reason to buy: The AWS 80 SC is one of the most attractive aluminium casement windows on the market, delivering slim sightlines, excellent performance, and the credibility that comes with the Schüco name. A top-tier option for premium residential or commercial projects.
Origin OW-70 Windows
The OW-70 is, in our view, Origin’s best product and a highly impressive aluminium window. Flush outside and stepped inside, it’s very attractive, and carries the Origin reputation and quality.
The sightlines are excellent, the look and feel are safe and reliable, and the market loves this particular window.
Reason to buy: OW-70 is a beautiful flush casement window with the Origin brand reputation and quality. It’s the reassuring option, but there are better and cheaper similar windows out there.
Origin OW-80 Windows
Origin invented the aluminium flush casement window with the OW-80. It is an outstanding window, save for its high cost and thick sightlines; otherwise, it would be another excellent aluminium flush casement window. Its unique feature among all the windows here is that it is flush inside and out, whereas all other brands are flush outside only.
The security with the trusted Yale brand, thermal performance, size capability and quality of OW-80 is excellent, as is the quality.
Reason to buy: The OW-80 has a look and feel like no other aluminium flush casement window, and it has the renowned Origin quality and reputation.
Reynaers Masterline 8 Heritage
Like Schuco, Reynaers are regarded by architects, designers, and discerning buyers as a luxury brand above mainstream brands like Aluk, Smart Systems, Origin, and others. Reynaers windows are superbly well-designed and engineered, and their specifications are reliable, trusted and rock solid.
The new Reynaers Masterline 8 Heritage is lovely, but its downside is that it is available as a tilt-and-turn window only. The upside is a unique-looking, distinctive and exclusive window. Its weather performance, security and insulation levels are also first class.
Reason to buy: Reynaers are distinctive, attractive windows with some of the best window specifications on the market and well worth looking into for your window project.
AluK 58BW Casement Windows
The staple aluminium window brand from Aluk, the 58BW is a long-established, tried and tested brand in the UK and generally excellent throughout. Aluk windows are rarely the best looking, but their specifications are spot on, and U-Values, acoustics, and weather performance are always accurate. The 58BW remains a dependable and proven option, particularly for trade installers and commercial projects.
The flush casement is widely used in apartments, new build homes with matching tilt and turn and contemporary window options. Aluk windows in our view favour reliable specifications and practicality over aesthetics.
Reason to buy: You can trust the Aluk brand and the 58BW is a reliable, well-designed, safe, secure and dependable window and where the slimmest of most modern styling isn’t top of your list.
Alunet Aluna and Aluna+ Windows
The existing Aluna windows are low-cost, simple to fabricate and new to the market.
The flush casement is a nice looking window which is accompanied by a choice of frame profiles to create virtually any style and design. Thermal performance is reasonable, the sightlines are slim and these are great for projects where you don’t need all the bells and whistles.
Reason to buy: There is a new enhanced Aluna + model in 2025 that promises substantial improvements over the original Aluna. Alunet windows do what they say on the tin and great for those on a budget and for investment property.
More information and where to buy flush casement windows.
While we consider the Alitherm 400, the best flush casement aluminium window right now, the ‘best’ very much depends on your own preference, budget and project type, replacement windows or new build. There is no bad window on the market, but where they differ is who makes them, the design and engineering and their price point. Whether you like their styling and, of course, confidence in the company quoting you also matters. But do bear in mind, that all windows are only as good as their manufacturing quality and their installation.
Some installers will gloss over the U-Values so always ask for the full specifications and how your windows meet the stated U-Values. Trickle vents will also be provided in most of these, adding to the sightline at the top frame. Or get in touch for window and door information and advice.
There are many other brands of windows, so do get in touch if you are quoted for a particular window and need more information on it and how it compares to our top choices here.
Since 2010, the Door and Window Experts Website has helped homeowners and the trade find the right products from the proper suppliers. Contact us for more information and to discuss your project.
