When you need new aluminium windows, whether as a replacement for existing windows or for a new building project, slimline aluminium windows can be a top priority for many buyers, over and above other features. Right now, Smart Systems provides the best in slimline aluminium windows.
If finding aluminium windows with the smallest frame face dimensions is important, we’ve taken the popular window brands in the UK and compared their key dimensions. We examine how each brand fares regarding fixed window frame sightlines, frame and opening sash sightlines, and mullion and transom dimensions. Three is no one size fits all slim aluminium window, and in this article, we explain why. Designs and sizes always affect how slim your windows can be.
Understanding slimline aluminium windows sightlines
The concept of sightlines in aluminium windows refers to the visible dimensions of the frame face, sash, and mullion/transom components when looking at the window from both the interior and exterior.
While focusing on dimensions is easy, it is also about styling. The frame design overall can make a difference in how slim a window can look. Contemporary windows with flat profiles tend to look slimmer than classically styled chamfered or ovolo windows, even if their measurements are larger. The best advice is always to view a selection of windows and get expert advice.
Comparing Major Aluminium Window Brands
To help you make an informed decision, we have compiled a comprehensive table comparing sightlines offered by some of the major aluminium window brands known for their slimline designs.
As we explain later in this article, four factors affect how slim your windows can actually be. So we have chosen the frame and vent combination more likey to be suitable for replacement window projects. New build openings can result in an alternative combination of profiles, reducing the sightlines even further.
Most window projects needing slimline aluminium windows will invariably have opening elements for ventilation. So the slimmest window is based on the Frame and Opening Sash Sightline dimension.
This image shows a popular window design with opening windows and fixed panels, on which we’ve based our table.
The Frame and Opening Sash sightline will be the most commonly used. Fixed pane frame Sightline refers to no opener. Mullion or Transom sightline assumes an opener either side of the mullion/transom.
| Brand | Frame and Opening Sash Face Sightline | Fixed Pane Frame Face Sightline | Mullion or Transom Face Sightline |
|---|---|---|---|
| Smart Systems Alitherm 300 | 59.5mm | 47.5mm | 111mm |
| Reynaers SlimLine 68 Classic | 65mm | 49mm | 110mm |
| Aluk 58BW | 65mm | 53mm | 100mm |
| Smart Systems Alitherm 800 | 70mm | 40.5mm | 112mm |
| Smart Systems Alitherm 400 | 71.5mm | 42mm | 116mm |
| Sheerline Classic | 71.5mm | 47mm | 98mm |
| Reynaers SlimLine 38 Classic | 72mm | 39mm | 127mm |
| aïr MOD Windows | 73mm | 48mm | 112mm |
| Schüco AWS70 | 76mm | 51mm | 148mm |
| Stellar Windows | 79.5mm | 54mm | 105mm |
| Senior Ali Vu | 84mm | 56mm | 108mm |
| Origin OW-70 | 85mm | 58.5mm | 107mm |
| Sheerline Prestige | 88mm | 46mm | 150mm |
| Origin OW-80 | 91mm | 50mm | 148mm |
The key takeaway from the face dimensions of the well-known brands is that there is very little to choose between them. You have an excellent choice of slimline aluminium windows overall.
All the above brands provide an excellent choice for slimline aluminium windows, but do also check out steel-look windows. Most of these can be even slimmer and all come with the option of all glass panes without astragal bars, making these look like regular modern windows.
Four factors affecting slimline aluminium windows
Four factors determine whether you can find the slimline aluminium windows you want and how slim these windows can realistically be.
The window design
The design of your new windows will always affect how slim these can be. By design, we mean whether your windows are mostly fixed panels or opening elements. If you want to create a floor-to-ceiling fixed picture window to look through a large pane of glass, then any quality window will give you slim sightlines. The Fixed Frame Face Sightline shows typical face dimensions.
The sightlines always increase when you add opening windows, as with most general window replacements and house styles. This is because a window needs three critical framing elements. These are the window’s outer frame, the opening sash, and mullions or transoms.
The window sizes
All window brands, system companies and designers provide a variety of frame profiles. This is because the window design combinations can be near-infinite. Window design companies, therefore, try to cater for most requirements with a choice of frame and sash designs and sizes.
The larger your window is overall, the less likely it is you can take advantage of all the smaller and slimmer profiles available. Window mullions, as one example, are designed to resist wind deflection and loadings. The slimmer the profile, the weaker it can be, meaning you must use a larger profile.
New build or existing window openings
Many of the marketing messages you may see promoting the slimmest windows are on the assumption these are for new build openings. New build openings can usually accept slimmer outer frames than existing openings where the internal plaster line and the structure’s nature need to be considered.
Only when a survey is done to establish the accurate window manufacturing sizes does a trained surveyor ascertain the most suitable frame profiles. Again these may not always be the slimmest.
The requirement for Trickle Ventilation
Under the current Building Regulations, new and existing window replacements must have trickle ventilators fitted. Some windows are designed to have trickle vents fitted in the existing frame head, but most will require an extension piece added to the top frame. This extension piece can vary from 15mm to 35mm.
Therefore, adding an extra frame profile or using a deeper outer frame for trickle ventilation will mean a larger sightline at the top of your windows.
Insights into slimline aluminium windows brands
Smart Systems Alitherm
With a fixed window frame sightline of 47.5mm and when you have an opening window of 59.5mm, the Alitherm 300 offers one of the slimmest sightlines among the major brands. Smart Systems are widely available through a nationwide network of quality manufacturers, and this brand is tried and tested, widely used, well-priced and stylish. The newer Alitherm 800 and 400 windows are also well worth considering. Alitherm tops the list when considering frame and opening element dimensions.
Reynaers SlimLine68
Harder to find but worth viewing are Reynaers Slimline 68 windows. Reynaers are an excellent window brand and stylish and slim. Depending on the frame and opening vent combination, Classic, Ferro or Cubic, you can go even smaller than the dimensions stated. You can find out more about the entire Reynaers range of aluminium windows.
Aluk 58BW
Like Smart Systems, Aluk is a great system to have in the home, and their 58BW offers pleasing sightlines with just 65mm with a frame and opening sash and slimline mullions. ALUK are another viable option for homeowners seeking slimline aluminium windows.
Sheerline Classic
When Sheerline first came out, we thought the beadless design was pointless and overcomplicated with concerns about who would want to service older windows in the future. You now have a standard beaded option with Sheerline Classic windows. These are now a competitive choice in the slimline market. The Prestige range is slightly thicker but offers nice styling for new build or replacement window projects.
aïr MOD Windows
Made in London by Everglade Windows, aïrMOD windows have lovely styling with the significant advantage of steel-look, tilt and turn and contemporary aluminium windows, all using similar frame profiles. We think this range offers a balanced and contemporary look for any home.
Origin OW-70
Origin OW-70 is a fantastic option for slimline aluminium windows, with superb quality and from a great British Brand. Slimmer frame sightlines are available with OW-70, but the smaller outer frame option may not suit all replacement window installations. Origin nonetheless is a highly attractive option for homeowners seeking elegance and performance.
Schüco AWS70
Schüco AWS70 stands out as arguably one of the best aluminium windows brands. There are numerous Schüco windows availablea and any of these promises a high-end window with sophisticated engineering and great styling. Schüco windows are, like Reynaers, not widely available in window showrooms. Get in touch and we can help with where to view these.
Senior Ali Vu
Based in Doncaster, Senior Architectural is widely specified by architects for new build homes and apartments. It isn’t easy to find Senior Ali Vu windows in window showrooms. They are well-designed, with excellent specifications and very appealing styling as another slimline aluminium windows option.
Conclusion
The best slimline aluminium windows won’t be the same for every project, and there are more advanced options by hiding the frames in the structure, where your design allows this.
Whilst slimline aluminium windows are important for many, you should also consider the overall window experience, not just how they look. The good news is that most brands today are slim, so you shouldn’t discount the brands with larger dimensions. But as you can see, the differences between all the well-known brands are surprisingly close, and again, it depends on the right frame and vent combination for your particular project. Your specific structural openings may mean even thinner dimensions than those shown.
When you want an unobstructed view or seek a balance between aesthetics and performance, the right slimline aluminium windows deliver. The larger the window, the less cluttered the frames will look. Smaller windows can look chunkier than larger and wider ones, even when using the same frame profiles. The best advice is to visit some quality showrooms and see a range or contact us for advice.
