Information about replacing Crittall Windows with aluminium.

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Nick Dardalis

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Do you have a house with old Crittall® windows or other steel casements? The options for replacing Crittall windows with aluminium are now substantial, especially for patio doors, with Alitherm, Aluco, Reynaers and other window brands providing a similar aluminium alternative. You will also benefit from substantially better security and energy efficiency over the old windows. This article provides information on what to consider with steel window refurbishment and the aluminium options for replacing steel windows.

what to consider when replacing Crittall windows with aluminium

replacing crittall windows with aluminium
Aluminium steel-look windows made by Everglade Windows of Middlesex.

If you do want to explore the aluminium options for replacing Crittall® windows,  as good as aluminium windows are, these are not 100% genuine replacements for the original steel product. Steel windows are much slimmer, they usually come with thinner glazing bars and if steel is the original, then steel replaces the original product correctly.

However, the cost of genuine steel windows is substantially more than the aluminium alternatives. Therefore, when not constrained by planning or other requirements requiring the genuine product, replacing Crittall windows with aluminium does provide a more affordable option. And when you choose the right product, the finished result looks great.

It’s also worth understanding the type of steel windows you’re replacing. Old metal windows have different names depending on when they were made. Windows from the 1920s may be the type called Universal Range. From the 1960s, you’ve probably got W20 windows installed. There’s also a product called SMW, meaning for Standard Metal Window.

Modern steel windows such as those made by Crittall® also meet today’s security and insulation requirements, having been significantly improved over the years.

The best products for steel window replacements

In aluminium, we think these brands provide some of the best options when replacing Crittall windows with aluminium. You can contact us for more information about all these brands and where to buy them.

Smart Systems Alitherm Heritage 47.

alitherm heritage windows in black fitted to london apartments replacing crittall windows with aluminium
Smart Systems Alitherm, works in modern apartments and most houses.

The Smart Systems Alitherm Heritage 47 is a remarkably well-designed aluminium window. This window suite creates steel-look windows, New York Screens, and a steel-look door.

One of the most popular brands providing the heritage and industrial look, Alitherm Heritage or Heritage 47 has an equally impressive French and single-hinged door option, a similarly styled bifolding door system and, more recently, an internal glazing system that is excellent.

aïr MOD aluminium windows

replacing crittall windows with aluminium showing white windows in a large house
aïrMOD windows fitted by alühome in Stamford.

The aïrMOD system offers an excellent selection of aluminium windows in a steel look, including contemporary, heritage and even a tilt and turn. The aïrMOD residential door system provides a patio door solution to match the windows.

aluco aluminium

aluco crittall style windows cost in a bathroom
Aluco Aluminium steel-look window in a textured grey finish and period handles

Expertly-crafted, beautifully styled and with gorgeous handle options, matching doors, bifold and internal steel-look doors and screens. Aluco is your go-to product from a smaller company providing windows and doors with genuine attention to detail.

AluK Optio 58BW ST steel replacement

steel patio doors
Aluk aluminium steel look windows.

The AluK Optio 58BW ST steel replacement window comes from another leading aluminium systems company.

The slimline profiles enable this window to be used in the home as well as commercially. AluK’s window is designed to replace old steel windows offering very slim sight lines and a credible aluminium alternative with high security and excellent thermal performance.

You can choose between 58mm or 70mm frame depths to suit new build and replacement applications. Other options include double glazed units up to 32mm, excellent security and a choice of what AluK calls Bay, Heritage or Contemporary profile appearance.

Finally, the AluK Option 58BW ST window comes as a fixed, multi-light, casement, bottom hung and multi-light arrangement.

Reynaers Slim Line 38 aluminium window.

steel look aluminium4 scaled
Five different styling options, give the most choice when replacing Crittall windows with aluminium

Also available from Reynaers is the SL38 suite of windows offering flexible design options as well as windows that can open in or out.

You have a choice of three different looks with the Reynaers SL38. There is Classic, Ferro and Cubic. Each of these is intended to offer a different visual look to a sliding aluminium window.

Classic offers a sloping detail to the outer frame and the opening sash. Cubic gives you a flat frame and sash. Ferro provides a flat external frame, but the sash features a projecting square nosing. All three are beautiful windows that are entirely different in appearance to the others we mention.

With the Reynaers SL 38, you get excellent weather performance, extensive colour choice, good U-Values and high security. Double and Triple Glazing is also available.

Also recently launched from Reynaers is the Slimline 68 aluminium window.  While not a steel look system, Reynaers SL68 offers very slim frames that would make it ideal for more basic window designs without the many horizontal bars found in metal windows. Reynaers are incredibly well-designed windows and should be checked out with other brands.

Replacing old steel windows.

If you can afford the luxury and the price premium, new steel windows are the way to go. New windows will retain much of the authenticity of your outgoing windows and steel specialists can advise, with many having an extensive range of products to choose from.

Is the sunshine bay available in Aluminium?

crittall bay windows
Image courtesy of

If you have old steel windows with one or two curved glazed sides, you may be wondering if it possible to replicate these in aluminium? The answer is yes if your chosen supplier has the skills and the suppliers to do it.

Curving aluminium sections on elevation (to create curved head windows) is much easier than curving on plan such as sunshine bays. Bending the spacer bars that separate the outer and inner pane of a double glazed unit is easy for those with the knowledge and skills to do it. Curved glass is also possible, but you will pay the price for having all these standard sections sent to a specialist section bender.

What you need to do is seek out a specialist company that can create aluminium sunshine bay windows. You’ll find more suppliers of standard windows and fewer that offer curves and shapes. We can help put you in touch with these. The less experienced company will want your work but offer flat glass and angled bays using bay poles. If you wish to the curved window to match your original seek out a company that can do it.

Current Buildings Regulations are sympathetic to period windows.

If you live in a period property, one in a conservation area or with planning constraints, always check with your local Authority or Conservation Officer.

Many local authorities do make allowances for properties with traditional windows or those of historical importance or architectural significance. Always seek professional advice.

Consider fitting authentic Crittall® Windows.

It is worth extolling the virtues of these windows and just how good they are. The fact remains, that while there are excellent aluminium alternatives, steel windows, look different and are different.  Once again, if you want the 100% authentic product, check out the unique windows and doors by Crittall®.

Longevity, construction and appearance are just three great reasons also to consider a steel window.  Some windows are still working today more than 90 years after being fitted.  No aluminium or plastic product has this service life, nor is it likely they ever will.  Steel windows feature galvanised steel, durable finishes, quality hardware and are built to last. Steel windows are also the slimmest.

Steel remains a super durable material giving these windows excellent security even when they are as slimmer than aluminium. Choose a steel window today, and you will get all the style, energy efficiency and high security you associate with a new PVCu, aluminium or timber window. The only drawback to steel windows is their cost when compared to other materials. However, given how long they will last, it is an excellent investment in your home. As well as this, properties with authentic steel windows and also very desirable to prospective buyers.

img 3134 e1509957868940
A typical house with original steel windows.  Consider replacing them carefully.

should you refurbish old steel windows?

One fantastic feature of old steel windows is how they work with the overall appearance of a house. Period homes are a favourite with homebuyers because of their character and original features. Windows are one of these. If you want to retain your original metal windows, refurbishment is one option. There are nationwide specialists in the restoration and renovation of steel windows, or you can seek advice and a suitable company from The Steel Windows Association.

Early generation steel windows will not be galvanised and probably worse for wear from corrosion; not helped by many different coats of paint over the years. The window hardware on original windows can be hard to replace if broken, and the putty may have failed as well. We suggest you seek advice from one of the specialists in restoration and get some initial advice.

In considering a repair to old steel windows, security and energy efficiency remain poor by modern standards. There is little you can do to improve it and this will be one compromise.

How can you repair old steel windows?

In deciding whether to repair or replace your old steel windows, your key concerns may be:

  • Improving Security.
  • Improving Energy Efficiency
  • Replacing your old single glass with double glazed units.
  • Reduction in noise levels
  • Improvement in weather resistance.

Depending upon the condition of the existing windows it may be possible to improve them in many of these areas. New seals, new handles, replacement glass and general refurbishment, are all offered by expert companies.

While you will not get the advantages of brand new thermally insulated windows, any good refurbishment provides some improvement over the old windows.

So what are your options for new windows in aluminium?

Secondary double glazing for steel windows.

It is worth mentioning Secondary Double Glazing. Secondary double glazing is an excellent alternative for houses with old metal or single glazed windows.  With secondary double glazing, you will usually find little resistance from conservation officers. Secondary double glazing is also substantially cheaper than new windows of any material.

Modern secondary double glazing is fitted behind original steel windows and is available in fixed, swing, lift-out and even sliding windows, meaning you should be able to retain the authentic look of your windows when viewed from the outside.

interior steel doors

Conclusion and Next Steps.

It is worth mentioning finally that all of the above systems should work well if you need them fitting in stone mullions or hardwood subframes.

All of the above products will give you all the advantages of new double glazed windows that will improve your home over existing steel windows. For us, the Smart Systems Alitherm Heritage 47 and the Reynaers SL24 and SL38 are the more appealing aluminium window residentially.

Installers like Alitherm windows also having a matching Alitherm Door as a single or double door set.

There are other specialist independent companies whose business is aluminium steel replacements. Examples include the Heritage Window Company in London with their Benenden Range, Jennyfields in Hampshire with their great steel windows that also create sunshine bays.

What these companies often do is take an existing system like the Alitherm and tweak it. They work with the systems company to modify the profile to make it different from the standard product and frequently will get exclusivity to it. There’s nothing wrong with this way of creating a more bespoke window. Aluminium systems companies are in the business of selling bars of aluminium and if they can do this for an independent installer, they will.

If you would like more information about steel replacement windows, and where to see them, contact us today. We can help put you in touch with suppliers and installers and answer your questions about replacing Crittall windows with aluminium.

Crittall® is a registered trademark of Crittall Windows Limited and is unconnected to the Aluminium Trade Supply Website.


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16:42 30 Oct 23
Nick responded incredibly quickly to my enquiry (on a Saturday too!), and was able to offer invaluable advice on both aluminum systems and manufacturer / suppliers. Thanks Nick!
chris steerchris steer
16:18 09 Oct 23
Had a meeting with Nick during the grand designs show. Was extremely helpful and professional would highly recommend
Chris WesthorpChris Westhorp
19:55 13 Sep 23
Extremely helpful with pointing us in the right direction to find the products we required and suggesting firms that could reliably fit them.Nick was quick to reply and very detailed in his advice.Highly recommend reaching out to them.
Cathy GreenwoodCathy Greenwood
07:03 11 Sep 23
Update - A second email to nick for help on bifolds resulted in a detailed informative reply even on a Sunday ! This guy is so knowledgable and helpful .I approached Nick for an independent view on sliding doors v bifold and the different brand options . His reply was extremely detailed and prompt and allowed me to navigate this often confusing world in a much more informed way . Thanks so much Nick
Anthony CraigAnthony Craig
12:45 05 Sep 23
This is a must site for anyone looking for advice. Great service and very quick answers to questions. Nick has been of great help quiding us through the maze of aluminium products. Thank you
Philip DuffieldPhilip Duffield
20:24 26 Jul 23
I contacted Nick @ ATS for guidance on what aluminium sliding door systems would be suitable for an opening in an extension that is going to be both wide and tall. He came back really quickly with very detailed and incredibly helpful advice. He is clearly extremely knowledgeable about the systems on the market and their respective features and capabilities. If you’re feeling a bit lost by the overwhelming range of choices out there, I’d definitely recommend contacting him.
Dariush HekmatDariush Hekmat
17:25 19 Jul 23
Nick's advice is great. He is always quick to respond and spends time on responses, which really help to make an informed decision.
Alan FosterAlan Foster
07:51 12 Jul 23
Absolutely fantastic. Asked for advice about replacing Crittall (?) windows late last night and early this morning received 3 great suggestions and contact information for suppliers
Rachel LauRachel Lau
09:24 16 Jun 23
Fantastic website full of valuable and pragmatic advice about product selection and comparison: no other website gives information like this. Truly written for public interest. Don't hesistate to reach out to Nick via the mailing system. He responds very quickly, is friendly, and has very sound and high knowledgable advice. I have already shared this with my friend planning her own grand design.
guard Charlieguard Charlie
12:28 14 May 23
I emailed this company just on the off chance they could help me with new magnetic sliders for my patio door. They were not able to supply those but were so very helpful providing me with the name of a company who could. I am so very grateful at the great service. Dare say customers must be very happy. thank you so much.
Benjamin LewisBenjamin Lewis
10:06 04 May 23
Nick is very helpful indeed. Extremely knowledgeable on bifolds which was in relation to my query. Great website as well, some very useful articles. Particularly appreciated the article that lists all the major bifold options in order of their sightlines! Thank you!
P JonesP Jones
08:07 15 Apr 23
I asked Nick some questions about an installation we were considering and he replied within hours with some very useful suggestions that will probably lead us to using a different make and supplier. Thanks, Nick. Great work.
Nicholas WallNicholas Wall
13:18 02 Apr 23
Looking for fair and honest expert advice on all aspect of aluminium windows and doors? These guys will arm you with all the information you need to make the RIGHT choice in a highly complex, crowded marketplace. post a question and you will get a very quick professional answer you can rely on being based on fact. Thanks guys!
Giorgia SiriacoGiorgia Siriaco
16:25 21 Mar 23
After a lot of research to find doors that would meet our unusual size requirements and feeling increasingly uncertain about the best way to spend our small budget, I stumbled on the ATS website, and I'm so glad I did! I contacted ATS to request advice and Nick promptly replied with a wealth of information, providing us with options and relevant contact details. I only wish I'd found them sooner!
Carol NortonCarol Norton
10:01 17 Mar 23
I've been so confused about how to achieve the look I'm after, and going round in circles with various window/door companies, trying to get away from the huge chunks of plastic currently around my windows. I didn't expect an email to a company found through a Google search to really help - but I was desperate, so I tried. I'm SO glad I did. Finally I have clear explanations from ATS of where I've been going wrong, exactly what I'm looking for, and a list of local companies that might be able to provide it! The response has excelled my expectations and I feel as if I'm finally inching closer to a home with which I'll be happy and comfortable: thank you.
David NunnDavid Nunn
20:54 14 Mar 23
It is rare that I write reviews, however after my very positive communication with Nick - enquiring about suitable slim sash aluminium windows for my project, I felt that a review was definitely warranted. I can reinforce the many positive reviews posted so far, Nick was very quick to respond, providing comprehensive detail, with excellent independent advice.In summary, great service, thank you Nick.
Chantal AuerbachChantal Auerbach
13:04 09 Mar 23
Nick from Aluminium Trade Supply was incredibly helpful informative and pleasant to deal with. He responded quickly to emails and was very knowledgeable. Highly recommend being in touch with Nick if you are considering new aluminium windows or doors.
Lee JonesLee Jones
20:21 22 Feb 23
I dropped Nick at Aluminium Trade Supply an email re high security slim sightline bi-folds and their alternatives and he responded that quickly (and so comprehensively) that I felt bad I’d not paid him for his time!Nick Sir your product knowledge is outstanding and you are providing a level of service that goes wayyyy above and beyond expectations. I’ll definitely make sure I mention Aluminium Trade Supply to anyone I encounter looking for a fenestration solution 🙏🏼
15:13 13 Feb 23
We are looking to replace some old UPVC patios doors with aluminium ones. The ATS website is a great source of advice in an area where clear information is sorely lacking. Having used the website, I then followed this up with a number of specific questions relating to our search, and Nick came back very quickly with clear, detailed and very useful advice.I have been very impressed with both the website and with Nick's advice. My only regret is that I didn't come across ATS before replacing various windows in 2021 - I'm sure it would have saved me a lot of grief and money! Thanks again Nick.
Azza McCabeAzza McCabe
17:47 01 Feb 23
So impressed with this company.Responded to my query quickly andgave valuable advice. Nick was extremely helpful and we were able to move forward with our project.
Adri LoloçiAdri Loloçi
11:21 08 Jan 23
Nick was super fast to respond and provided some great recommendations. I would recommend this website to anyone looking to find bifold or sliding aluminium doors.
Stephen HoustonStephen Houston
16:16 03 Jan 23
Looking for aluminium crittall style internal door and external patio French doors. Noted good reviews and thought would ask for advice. Comprehensive reply with excellent independent advice and lists of fitters who could provide products and installation. Great service.
Inga GeachInga Geach
08:25 21 Dec 22
Nick from Aluminium Trade Supply has been extremely helpful with navigating the jungle that is aluminium glazing for our upcoming extension project. His advice was prompt, detailed and always impartial. Very grateful for your input, thanks Nick!
Amanda BurtonAmanda Burton
10:54 16 Dec 22
Brilliant website and an excellent service. Nick provided not only detailed advice and supplier contacts, but highlighted the considerations of various products so I could make an informed choice. Our Sunvista minimal sliders were fitted this week and I couldn't be happier, stunning. Thanks once again for your advice and recommendations, invaluable!
Keith BarnesKeith Barnes
17:18 10 Dec 22
Very helpful advice given to my question, including the name of 3 different companies that i could try for the product being enquired about. Many thanks
Munim ChowdhuryMunim Chowdhury
11:45 13 Sep 22
Nick has been very helpful on signposting me to a number of partner organisations for steel/aluminium doors.
SUSAN wallaceSUSAN wallace
17:26 31 Aug 22
My experience with this firm was exceptionally good and this is notalways the case as a female, dipping a toe into technical waters.I was spoken too with courtesy and at a level that helped me consolidate what was needed .On top of that I was given a list of companies and places where I could obtain the type of product I needed.I could not thank them enough and would certainly go there again and reccommend others do too.
Paul SalterPaul Salter
22:39 22 Aug 22
Contacting Aluminium Trade Supply is like contacting the Oracle direct. Advice is always comprehensive and balanced. On multiple occasions they have provided me with options that fully meet our objectives. Many thanks.
Nick McCormackNick McCormack
20:25 14 Aug 22
Really helpful and useful came back to me on a Sunday with some invaluable information. Highly recommended.
ray addisonray addison
13:14 14 Aug 22
received a prompt reply to my query,and helpful information from ATS