Crittall® vs Aluminium Heritage Windows: Cost, Pros & Cons

Torn between genuine steel windows and modern aluminium replicas? We compare cost, thermal efficiency, and explore the UK’s leading aluminium systems: Smart Alitherm and Sheerline Classic.

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Aluminium heritage windows flawlessly replicate the iconic slim sightlines of traditional steel.

The iconic, slimline, grid-style window has experienced a massive resurgence in UK home design. Originally pioneered by Crittall® in the 1880s using solid steel, this industrial look is now the highly sought-after aesthetic for rear extensions, garden rooms, and heritage replacements.

But when planning a renovation, homeowners face a critical choice: do you pay the bespoke premium for highly authentic genuine steel, or do you choose modern thermally broken aluminium windows designed to mimic the steel aesthetic?

1. Interactive: Find the Right Window for Your Home

Not sure if you should pay the premium for real steel? Answer 2 quick questions below to see our expert recommendation based on your specific property.

2. Quick Compare: Steel vs Smart vs Sheerline

If you need the data at a quick glance, here is how the genuine historical article stacks up against the UK’s two leading modern aluminium alternatives.

3. Real-World Cost Examples (££ vs ££££)

Cost is often the deciding factor for our clients. Because steel window fabrication involves heavy, highly intensive manual welding and craftsmanship, it commands a luxury, bespoke price point.

To put this into a real-world perspective:

• Genuine Steel: A full window replacement on a standard 3-bed semi-detached house in genuine steel can easily exceed £30,000 to £35,000+.
• Premium Aluminium (Smart or Sheerline): Replacing those exact same windows using high-quality, thermally-broken aluminium heritage replicas typically falls between £15,000 and £20,000 (depending on specifications and final sizes).

4. What Homeowners Worry About (And the Reality)

When clients visit our showroom, they usually arrive with a few key emotional concerns regarding this style of window. Let’s address the realities.

“Will aluminium look fake or chunky?”

The Reality: No. Both Smart and Sheerline systems were engineered specifically to solve this problem. Sheerline Classic, for example, achieves incredibly slim sightlines of just 59mm. Unless an architectural historian inspects the joints with a magnifying glass, 99% of people cannot tell the difference from the street.

“Will grid-style windows make my house cold?”

The Reality: If you install old, single-glazed steel, yes. Steel naturally conducts cold from the outside in. However, modern aluminium heritage frames feature advanced thermal breaks (like Sheerline’s Thermlock® closed-cell barriers) that stop cold transfer dead in its tracks. You get the industrial look with A-rated warmth.

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Stunning aesthetics: The slim profile of heritage aluminium used as an internal partition heritage door.

5. Steel vs Aluminium: The Performance Battle

6. Smart Alitherm vs. Sheerline: Which Aluminium System?

Once you have decided that the immense benefits of aluminium outweigh the cost of steel, you have another choice. At KJM Group, we refuse to supply just one brand. We install the UK’s two finest heritage systems: Smart Alitherm and Sheerline Classic/Heritage. But which is better?

Smart Alitherm Heritage: The Established Classic

The Smart system is arguably the most famous aluminium heritage window in the UK. It is brilliant at replicating the classic stepped profile of old steel windows and offers an extensive suite of beautiful, period-accurate hardware (such as traditional Monkey Tail and Bulb peg stays). It is the perfect choice for replacing 1930s Art Deco windows.

Sheerline Classic / Heritage: The Modern Innovator

Sheerline is a newer, ultra-premium system that focuses heavily on cutting-edge engineering and security. It offers a distinct advantage in two main areas:

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The internal engineering of a Sheerline Heritage window, showcasing the multi-chambered Thermlock® technology.

• Beadless Security: Traditional windows use glazing beads to hold the glass in place. Sheerline is completely beadless; the glass is bonded directly into the frame from the inside. This creates flawless, unbroken exterior lines and makes the window exceptionally secure against intruders.
• Thermlock® Technology: Instead of a standard polyamide thermal break, Sheerline uses proprietary closed-cell, multi-chambered thermal breaks, achieving phenomenal U-Values that easily surpass new building regulations.

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Sheerline French doors provide a stunning, highly secure “Crittall-style” aesthetic for modern extensions.

7. When NOT to Choose Aluminium

At KJM Group, we believe in honest advice. While aluminium is perfect for 95% of homes, there is one scenario where you should absolutely not choose it:

8. Frequently Asked Questions