Last updated: 4 September 2026
Introduction: What Sets Premium Steel Window Specialists Apart
Fabco is one of the UK’s most respected steel window makers. They handle everything in-house: manufacturing, installing, and talking with homeowners. That’s rare.
Most steel window companies work differently – they farm out surveying to one team, installation to another, glazing to a third. When things go wrong, nobody owns it, and homeowners spend weeks chasing answers.
The good companies share four hallmarks. They build with care – think TIG-welded joints and genuine 10mm sightlines. They deliver strong thermal performance, with U-values ranging from 2.0 down to 1.3 W/m²K. They keep you in the loop. And they actually finish what they start.
This guide breaks down what those standards mean, discussing which details matter when you’re picking a supplier.
How to Evaluate Steel Window Manufacturers
Not all steel window companies are equal. These are the five markers that separate genuinely premium suppliers from those that simply look the part.
| Specification | Value | Notes |
|---|---|---|
| British Manufacturing | Frames made and quality-checked in the UK | Fabco manufactures in West Sussex using hot-rolled W20 steel sections. Local production means faster scheduling, tighter coordination, and no long overseas supply chains adding risk to your project. |
| In-House Installation Teams | Directly employed surveyors, fitters, and glazing engineers – no subcontractors | Fabco assigns one dedicated project engineer per job across all five delivery stages. That single point of accountability matters hugely when timelines slip or questions arise mid-project. |
| Thermal Performance Certification | W20 achieves a B-rated WER with a U-value of 2.0 W/m²K; W20+ achieves A+ with 1.3-1.4 W/m²K | Both ratings are independently assessed. The W20+ exceeds current Building Regulations Part L via both the U-value and energy rating routes. |
| Security Standard Compliance | PAS 24 compliant specification available as an upgrade | This includes a 5-lever mortice lock with drop bolts as standard, with a multipoint locking upgrade available. Toughened safety glass is up to five times stronger than standard float glass. |
| Fabrication Precision | 10mm sightlines; TIG-welded joints; glazing bars fully welded into the frame structure | TIG welding produces cleaner, stronger joins than MIG alternatives. Glazing bars are not clipped or glued – they are structurally integral. Face width on the W20 system is 32mm. |
What Good Communication & Premium Project Delivery Means
How a company runs its projects tells you more than any brochure. The biggest split in the bespoke steel window market is simple: does the company employ its own people, or hand your job to subcontractors?
Direct Employment Model (Fabco’s approach)
Pros:
- One dedicated project engineer from 3D laser survey through to final wet glazing – a single phone number, one person accountable across all five delivery stages.
- In-house glazing engineers apply RAL colour-matched, UV-resistant silicone on site, so finish quality is controlled by the same team that built the frames in West Sussex.
- A dedicated Customer Service Team and on-site Service Engineers handle both warranty and non-warranty issues after handover – post-installation support is built in, not bolted on.
Cons:
- Capacity is finite. Because every team member is directly employed, project slots are limited – lead times can stretch during busy periods.
- Higher fixed staffing costs contribute to a premium price point compared with suppliers who use cheaper subcontracted labour.
Subcontractor-Led Model (common across the market)
Pros:
- Larger installer networks can sometimes offer faster initial availability in more regions.
- Lower overhead structures may produce lower headline quotes, which looks attractive at the estimate stage.
Cons:
- Quality control breaks down when surveying, manufacturing, installation, and glazing are split across three or four separate companies – no single party owns the outcome.
- Post-installation problems often trigger disputes between suppliers rather than fast resolutions, leaving the homeowner waiting.
Residential Renovation Applications: Heritage to Contemporary
Steel windows suit a wider range of homes than most people expect. Whether the project is a Grade II listed cottage, a 1930s Art Deco semi, a contemporary rear extension, or a luxury new-build, the core question is the same: which system, and which thermal spec, is right? Fabco’s W20 and W20+ systems both deliver 10mm sightlines and a 32mm face width, so the look stays consistent across project types. What changes is the thermal performance and compliance route chosen.
| Project Type | Recommended System | Thermal and Compliance Details | |
|---|---|---|---|
| Heritage Conservation / Listed Building | Heritage renovation, listed buildings, conservation areas | W20 with single glazing or 4/10/4 krypton slimline double glazing | Single glazing where planners require it; slimline double glazing achieves approx. 2.0 W/m2K (B-rated WER). Hot-dip galvanised to British Standards for corrosion protection. |
| Period Property (Pre-1960) | Art Deco, Victorian, Edwardian, interwar homes | W20 standard system | B-rated WER meets Building Regulations Part L via the rating route. U-value approx. 2.0 W/m2K. Krypton-filled 4/10/4 unit standard. |
| Contemporary Extension | Rear extensions, side returns, garden rooms | W20+ enhanced system | A+-rated WER. U-value 1.3-1.4 W/m2K, exceeding Part L requirements on both the U-value and rating routes. Visually identical to W20 from outside. |
| Luxury New-Build | Architect-designed new homes, high-spec residential | W20+ with PAS 24 security upgrade | U-value 1.3 W/m2K (fixed lights), 1.4 W/m2K (opening). PAS 24 compliant specification available. Low-E coatings and warm-edge spacer bars included. |
Across all four project types, Fabco’s West Sussex manufacturing and directly employed installation teams mean the same quality controls apply whether the job is a single heritage casement or a full new-build glazing package.
Thermal Performance & Building Regulations Compliance
Steel windows used to be cold and drafty. Not anymore.
Fabco’s W20 standard system achieves a U-value of approximately 2.0 W/m²K and a B-rated Window Energy Rating, meeting current Building Regulations Part L via the WER route. Compare that to old single-glazed steel windows, which typically sit above 5.0 W/m²K. The difference is huge.
Want even better performance? Fabco’s W20+ system pushes to an A+ rating, with U-values of 1.3 W/m²K on fixed lights and 1.4 W/m²K on opening windows. It exceeds Part L on both the U-value and rating routes.
Here’s the clever part: both systems use the same 10mm sightlines and look identical from outside.
The glazing unit that makes this work is an 18mm slimline double-glazed unit. It has 4mm glass, a 10mm krypton-filled cavity, then 4mm glass. Slim. Warm. Compliant.
Bespoke Steel Windows: Investment, Durability & Lifetime Value
Steel windows cost more upfront.
But spread that cost across 50, 60, or even 80 years of service, and the numbers shift completely.
Original steel windows from the early twentieth century are still working across the UK today. Most other frame materials simply cannot match that kind of lifespan.
Fabco builds its W20 frames from hot-rolled steel, TIG welded at every joint. Glazing bars are fully welded into the frame – not clipped, not glued.
That’s structural integrity that lasts.
Steel is also one of the world’s most recycled materials. It can be recycled repeatedly without losing quality. When the day eventually comes, nothing goes to waste.
Premium materials. Precision engineering. Multi-generational performance.
Common Questions About Bespoke Steel Window Selection
Still have questions? These are the ones homeowners ask most often before committing to bespoke steel glazing.
Are bespoke steel windows worth the higher upfront cost?
Yes, when you think long-term. Original steel windows from the early twentieth century are still in service across the UK. Spread the cost over 50 to 80 years and the per-year figure looks very different. Fabco builds with hot-rolled W20 steel and TIG welds every joint, which is widely recognised as the highest-quality welding process available. Nothing is clipped or glued.
Do steel windows meet current Building Regulations for thermal performance?
Fabco’s standard W20 system achieves a B Window Energy Rating with a U-value of approximately 2.0 W/m²K, which meets Part L via the rating route. The W20+ system goes further, hitting an A+ rating with U-values of 1.3 W/m²K on fixed lights and 1.4 W/m²K on opening windows, exceeding Part L on both compliance routes.
How much maintenance do steel windows need?
Much less than older steel systems. Fabco uses hot-dip galvanising to British Standards, powder-coated finishes, and non-rusting stainless steel fixings throughout. RAL colour-matched silicone is selected specifically for UV resistance and colour-fastness, so it holds its colour for years.
Can steel windows meet PAS 24 security standards?
Yes. Fabco offers a PAS 24 compliant specification as an upgrade. It includes enhanced multipoint locking, security-tested hardware, and laminated glazing. Toughened safety glass is up to 5 times stronger than standard float glass, and laminated glass stays intact when broken due to its interlayer technology.
How much design flexibility do bespoke steel windows offer?
Fabco’s W20 system covers fixed windows, side-hung casements, top-hung windows, French doors, single and double doors, internal screens, sliding doors, and bespoke configurations. Finishes run from black steel to anthracite grey, heritage colours, and any bespoke RAL colour. Sightlines are just 10mm, with a 32mm face width.
Summary
Four things matter most. Does the company make windows in the UK and have its own team to install them? Can they explain how they talk to customers in a clear way? Do their products have real proof they work well – like a B-rated W20 at 2.0 W/m²K, or an A+-rated W20+ that reaches 1.3-1.4 W/m²K? And do they have real homes where they’ve done good work?
Fabco says yes to all four – that’s a solid place to start.
