What is the best Aluminium Flush Casement Window?

Photo of author

Nick Dardalis

Origin Frames, leading bifolding door manufacturers When Origin launched their new aluminium window, it was the first of its kind to offer a flush casement. The latest generation Origin aluminium window still remains relatively unique amongst aluminium windows and rather ‘one of a kind’.  It provides a flush sash on the inside of the window as well.  We think the current Origin Twin Flush window is arguably the best Aluminium Flush Casement Window on the market.  But we wanted to do some comparisons.

Since the Origin aluminium window became available, it has had little by way of direct competition. Recently we have seen the introduction of Warmcore aluminium windows and a rather impressive window from Senior Architectural.

Why choose a flush casement window?

flush sash windows are all different with origin offering a great design viewed from the inside as well.
Flush Sash windows are all different with Origin offering a great design viewed from the inside as well.

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, and there are some terrific products about such as those from Residence 9.

The PVCu industry tends to market their flush casement windows as a solution for the replacement of traditional 19th Century timber windows.  In aluminium, the flush window message to consumers is somewhat mixed.  Most are marketing their flush casement windows as both suitable for the replacement of old timber windows as well as a contemporary aluminium window.

In our experience, flush casement windows can look better than traditional overlapping vents, but it does depend on the overall window design too.

Origin remains the only Company offering an all aluminium flush casement window, therefore they don’t have much by way of way of direct competition. However, anyone looking at buying windows is bound to consider alternatives and seek to find comparisons and this is where we try to help.

Alongside the Origin Twin Flush Window, we are choosing to look at the following alternative systems.

  • Warmcore Aluminium Windows
  • Senior Aluminium Series 2

It was also highly tempting to include the very attractive Lumi Seamless Glazing from Apeer. We decided against this because it is more a frameless system rather than a flush casement.  Another aluminium system that provides a flush casement windows Senior PURe windows. It was decided not to include this because the detail is on the inside only rather than the outside.  We consider the external aspect more important on a flush casement window.

Finally, there are also flush sash windows to be found in hybrid windows, those that feature timber inside and aluminium outside.  Given the different materials and construction, it is debatable whether these can be considered to compare against an all aluminium window.

How is a flush casement window designed?

The first thing that stands out between Origin, Warmcore and Senior is how the flush sash detail is designed.  Dig into the technical aspects of the windows and only Origin have made the flush casement in their Twin Flush window without needing an additional section to create the lip. This is ingenious engineering and design by Origin. Warmcore windows rely on a separate extrusion positioned at the front of the window to provide the flush appearance.

Senior Aluminium Series 2 is also a highly attractive window but it is quite involved in its construction. A typical window features seven different extrusions. For the average consumer or anyone buying in these windows it makes no difference, but it demonstrates the differences between the systems and the approach systems companies take to designing them.

Senior Aluminium Series 2 windows are identical to their Hybrid Series 2 and the do look different to Origin and Warmcore when viewed from the outside. We feel Senior should be compared against Origin and Warmcore as a credible option.

Comparing Origin, Warmcore and Senior Flush Casement Windows.

All three systems are excellent and fit for purpose. They offer different solutions for both installers and consumers. Aesthetically all windows are good to look at as well. We’ve created a simple chart that lists the features of the three windows reviewed here.

Comparing Origin, Warmcore and Senior Flush Casement Windows.
Origin Twin Flush Window Warmcore Windows Senior Aluminium Series 2
*Origin offer a 20 year guarantee on their windows directly. Warmcore and Senior guarantees will typically be 10 years by their installers. U Values may vary depending on glass specification and optional upgrades *** Profile height is based on an opening light set on a standard cill section.
Correct as of July 2016
Choice of Frame Profiles NO FOUR NO
Choice of Bead Style NO YES NO
Triple Glazed Option YES Yes YES
Security Tested YES YES YES
Severe Weather Rating YES YES YES
U Values** WM2K 0.9 0.8 0.95
Insulation Upgrade AEROGEL NONE FOAM
Profile Height*** 116mm 117.5 54mm
Frame Depth 80mm 85mm 142mm
Full RAL colour range YES YES YES
Dual Colour Option YES YES YES
Wood effect finishes YES NO NO
Anodised finishes NO NO YES
Maximum Vent Height 1500mm 1200mm 1584mm
Colour Matched Handles YES NO NO
Tilt and Turn Option NO YES NO
Matching Doors YES YES NO

Origin Windows.

The Origin Twin flush windows offer the same detail internally and we consider this window superb in its design, performance and range of options available. One of the best features of the Origin Twin Flush window is the colour matched handles. It is immensely difficult to paint window handles in a variety of colours and Origin manage to do this where others either cannot or refuse to do so because of the complexity.

There is a small issue with Origin windows when required for replacement window installations.  The outer frame is quite narrow and perfect for new builds. When Origin windows are needed to replace old windows often an add-on section will be required. Of course, every installation will be different however using an add-on section does add to the visible sight lines of the window with a groove visible where the add-on meets the outer frame.

Senior Aluminium Series 2.

Study the marketing literature around the Senior window and it is easy to assume that this is a commercial window only. We see no reason why it could not be used residentially. The frame depth is substantially larger front to back than Origin or Warmcore but it is also much slimmer on the profile faces. There doesn’t appear to be a huge choice of handles and upgrades available with the window but we forgive all that because the window looks so slim.

Internally the deeper frame that leads back from the glass line may not be to everyone’s taste. These windows were designed to replicate the aesthetics of their Hybrid suite of windows in an all aluminium alternative. The Senior Hybrid range of windows is some of the best you can buy,

Warmcore Windows

Warmcore offers four choices of frames and two options of glazing bead with a different bead for triple glazed windows. This makes for a highly flexible window system that should appeal to those wanting a contemporary and a traditional sculptured window.  There is also a tilt and turn option with Warmcore that the other systems do not provide.

Complimentary doors and windows.

Senior Architectural  is the only company that doesn’t offer a matching range of doors with their Aluminium Series 2 product. Origin offer bifolding, single doors and French doors as do Warmcore.

How to buy Flush Casement Windows.

Origin is the only fabricator of their windows. The trade wanting to buy Origin windows buys them from Origin and consumers purchase them through their network of manufacturers.

Warmcore and Senior are available through a network of approved fabricators.  Both systems are marketed as easy to make with no significant additional tooling or extensive changes to fabrication methods required.

Lead Times

Origin continues to lead the industry with fast lead times on aluminium windows.  As they are in control of their supply chain this enables them to offer windows in one week.  The exception is the window with the Aerogel upgrade or individual colours which are subject to 3 week lead times.

Warmcore windows are available on reasonably good lead times as well.  Senior will supply the coated extrusions to their network of fabricators so lead times will vary depending on the individual manufacturers workload.


Again Origin comes out on top with their guarantees. They offer the same industry leading 20-year warranty that you get on their bifolding doors. Synseal offers a ten-year guarantee with their Warmcore windows but we understand this is honoured by the installing company rather than the systems company. There is also a guarantee of 10 years on the profiles and powder coated finish. Senior Systems windows will be subject to whatever warranty is offered by their manufacturer/installers.

What is the best aluminium flush casement window?

It is quite challenging accurately to compare these three very different aluminium flush sash windows. Only the Warmcore and the Origin windows are quite a close match visually with the Senior window slimmer and entirely different.  So let’s look at each one individually.

Looking for aluminium windows? Consider windows by Senior Architectural Systems.

you won't often see senior windows in a window showroom but you will find them in some of the best modern buildings.
You won’t often see Senior Windows in a window showroom but you will find them in some of the best apartments and houses.

Senior Aluminium Systems are an excellent systems company yet a bit of an enigma. The entire range of Windows by Senior Aluminium are superb in our professional opinion. We have worked with Senior products over the years and love how well designed they are as well as very fabricator and fitter friendly.  They are well priced too.

It remains a real mystery why so few retail showrooms feature Senior windows and doors.  Senior are at the cutting edge of window design offering a big range of windows meeting virtually every window need.

Look at Senior windows and you will find a fantastic range of hybrid windows, a brilliant fibreglass window and a highly innovative range of aluminium windows in their PURe range and Aluminium Series 2. So why don’t we see more retail showrooms selling Senior Windows?

What we do know is that manufacturers of Senior windows and doors are plentiful but in our experience the focus of work is towards the commercial and specification sector.  For commercial work Senior have an excellent reputation and standing. While a consumer may not usually go for Senior Windows directly, a vast number of new build apartments and houses have Senior windows fitted. Contractually this work may be regarded as commercial, however the result is still a  dwelling.

We understand that Senior Systems are soon to launch an extensive marketing campaign targeted towards the end user.  They have now brought out the PURe range of windows that are excellent and comprise a full door and window suite with hinged doors, sliding doors and bifolding doors alongside PURe windows. We have seen these products and are impressed by their design, appearance and ease of fabrication.

We hope Senior Architectural does become as well known for residential windows as they are commercial. We now see the market somewhat saturated with many similar systems such as Smarts and AluK and we would urge window installers and homeowners to look at other great systems such as Senior Architectural.

Origin Twin Flush Windows.

the origin twin flush window is superbly made and executed.
The Origin twin flush window is superbly made and executed.

Origin needs little introduction as they are firmly established as one of the best aluminium providers in the UK today. Their bifolding doors are industry leading, the Origin service is 1st Class and the quality of Origin products is consistent. Talk to any Origin Dealer and they love how looked after they feel by Origin and consumers have no problem with the engagement Origin chooses to have with them.

Origin’s Twin Flush window is a terrific product. It looks good, it has some impressive specifications and it has a 20-year guarantee.

Some people we talk to consider Origin windows a little bulky compared to regular aluminium windows but once again aesthetics is a personal view that not everyone will share. With an Origin window you’ll get a direct source of supply, super fast lead times and a great customer experience.

Warmcore Aluminium Windows.

picture of warmcore tilt and turn window.
Warmcore is set to become a very popular window in the coming years.

It has surprised us how the window industry has embraced Warmcore.  The main advantage of the Warmcore window is its frame choices. This makes it a flexible window that should appeal to those that may not desire a flat contemporary window. Its thermal performance is great and you will get matching doors as well.

We think Warmcore gives a new route to market to established aluminium providers. Warmcore is made entirely differently to a polyamide aluminium window and therefore enables an installer to upsell it or at least show a customer how window innovation has moved forward and provide them with a choice. Synseal is also a very reputable systems company and everyone comments on how good the service levels and support are.

Origin we feel is the better window for aesthetics, a superb guarantee, the availability of colour matched hardware and its consistent quality aspect. Warmcore we like because it offers frame choices which are always a bonus when choosing a window.If you are looking for a window few are likely to have in their homes then Senior windows will provide a more individual window.  It looks different from the rest and is very well designed.


Images courtesy or Origin and Synseal Systems/Warmcore.