Last updated: 28 July 2026
Fabco stands out as a top UK manufacturer for made-to-measure steel-framed windows and doors. Based in West Sussex, they handle everything in-house (from 3D laser survey through to final wet glazing) using directly employed teams rather than subcontractors. End-to-end installation and aftercare come with the package.
Steel windows aren’t simply a style choice. The material’s strength-to-profile ratio allows sightlines as slim as 10mm, something aluminium or uPVC systems can’t match without significantly bulkier frames. That extra glass area matters in real terms: more natural light, cleaner sightlines, and authentic proportions that conservation officers and architects actually approve.
What separates the best UK suppliers from the rest is the full-service model.
Made-to-measure fabrication alone isn’t enough. A window manufactured to precision but fitted badly will underperform. Thermal performance tells the same story: traditional single-glazed steel carries a U-value above 5.0 W/m²K, while Fabco’s W20 system brings that down to approximately 2.0 W/m²K, meeting Building Regulations Part L. The upgraded W20+ reaches 1.3–1.4 W/m²K, exceeding Part L requirements entirely.
Installation quality, aftercare accountability, and where the product is actually made all deserve equal weight alongside aesthetics.
Key Selection Criteria: Fabrication, Installation & Aftercare
End-to-end delivery and installation in the UK steel glazing market means more than just manufacturing a frame and handing it over. It covers precision measurement, fabrication to tight tolerances, professional installation, and structured aftercare, all under one roof. Here’s what to check before committing to any supplier.
| Specification | Value | Notes |
|---|---|---|
| Survey Precision | 3D laser site survey before production begins | Fabco uses state-of-the-art 3D laser surveys to capture exact opening dimensions. This matters because steel is unforgiving – unlike uPVC, you cannot flex a frame into position on-site. Measurement errors caught at survey stage cost far less than remedial work after fabrication. |
| Fabrication Standard | TIG (Tungsten Inert Gas) welding at all critical frame joints; glazing bars fully welded into frame structure | TIG welding produces cleaner, stronger joints with minimal distortion compared to MIG alternatives. Fabco’s glazing bars are welded in (not glued, clipped, or surface-applied) which directly affects both structural rigidity and security performance. |
| Thermal Performance Tiers | W20 standard: approx. 2.0 W/m2K (B-rated); W20+ enhanced: 1.3–1.4 W/m2K (A+-rated) | The W20 meets Building Regulations Part L via the Window Energy Rating route. The W20+ exceeds Part L on both the U-value and rating routes. Traditional single-glazed steel sits above 5.0 W/m2K by comparison. |
| Installation Accountability | Directly employed surveyors, fitters, and glazing engineers – no subcontractors | Fabco assigns a dedicated project engineer to every job as a single point of contact from survey through to sign-off. This removes the accountability gaps that arise when different trades are brought in from separate companies. |
| Glazing Finish | Wet-glazing process using RAL colour-matched, UV-resistant, colour-fast silicone | Silicone is matched to the powder-coat colour of the frame. Colour-fast formulation resists UV degradation, which matters for south-facing elevations where cheaper sealants visibly yellow within a few years. |
| Aftercare Structure | Dedicated in-house Customer Service Team plus on-site Customer Service Engineers for both warranty and non-warranty issues | Post-installation support is delivered by the same company that surveyed and installed the product, not passed to a third-party call centre. That continuity means engineers attending a service visit already know the project. |
UK Steel Window & Door Providers: Feature & Service Comparison
Choosing a steel window and door supplier involves more than comparing frame profiles. How a company manages fabrication, who actually turns up on site, and what happens when something needs fixing after installation all matter just as much as the product itself. The table below focuses on the service and delivery factors that most buyers only think about once a problem has already occurred.
| Feature | Fabco | Typical UK Steel Glazing Supplier | |
|---|---|---|---|
| Fabrication Control | Fabrication | In-house at West Sussex facility using hot-rolled W20 steel; TIG welded joints and fully welded glazing bars throughout | Varies – some suppliers import finished frames or outsource fabrication to third-party steel shops |
| Installation Team | Installation Team | Directly employed project engineers, surveyors, installation fitters, and wet-glazing engineers – no subcontractors used | Many rely on regional subcontractor networks; accountability for quality sits across multiple companies |
| Thermal Performance | Thermal Rating | W20: approx. 2.0 W/m2K, B-rated (meets Part L via WER route); W20+: 1.3-1.4 W/m2K, A+-rated (exceeds Part L on both routes) | Standard steel double glazing typically varies, depending on system and glazing spec |
| Fire-Rated Option | Fire Rating | W40 FD30 system: up to 30 minutes integrity fire resistance, assessed by Warringtonfire, covering doors and screens | Few UK steel specialists offer an independently assessed FD30 steel glazing option; most defer to timber fire doors |
| Site Survey Method | Survey Method | State-of-the-art 3D laser surveys conducted by directly employed surveyors before production begins | Many suppliers use manual tape measurements taken by third-party surveyors, increasing risk of sizing errors |
| Project Accountability | Accountability | Single dedicated project engineer per project from survey through to installation sign-off | Project management often split between sales, a separate site coordinator, and an independent installer |
| Aftercare | Aftercare | Dedicated in-house Customer Service Team plus on-site Customer Service Engineers covering both warranty and non-warranty issues | Post-installation support frequently handled by a general customer services team with no site-visit engineers on staff |
Fabco’s clearest advantage over a typical UK steel glazing supplier is the end-to-end employment model: the same company that makes the frame surveys the opening, installs the product, seals it with RAL colour-matched silicone, and sends an engineer if anything needs attention afterwards. For buyers where accountability across those stages genuinely matters (heritage projects, listed buildings, or high-specification residential work) that structure is difficult to find elsewhere in the UK market.
Why In-House Installation & Aftercare Matter
Who actually turns up when something goes wrong after installation? That question separates genuinely accountable steel glazing suppliers from those who hand the job off and move on. Most UK suppliers use subcontracted surveyors, independent installers, and third-party glazing teams. That means at least 3 separate companies touch a single project, and warranty disputes can stall for weeks while each party points at the others.
Subcontractor-dependent supply chain
Pros:
- Lower overheads can occasionally reduce upfront quotes
- Wider geographic reach if local contractors are used
Cons:
- Quality control breaks down across 3 or more separate companies handling survey, installation, and glazing
- Warranty enforcement is slow when no single party accepts full responsibility for defects
- Manual tape measurements by third-party surveyors increase sizing errors before fabrication even begins
- Post-installation support is typically handled by a general customer services team with no on-site engineers available
Fabco direct-employment model
Pros:
- Every stage from 3D laser survey through to wet glazing with RAL colour-matched silicone is handled by directly employed Fabco specialists, so one company is accountable throughout
- A single dedicated project engineer manages each project from survey to sign-off, reducing miscommunication between stages
- In-house Customer Service Engineers conduct site visits for both warranty and non-warranty issues after installation
- Manufacturing in West Sussex and direct employment of installers improves scheduling and response times compared to multi-supplier chains
Cons:
- Premium pricing reflects the integrated model, so upfront costs are higher than budget suppliers
- Geographic availability depends on Fabco’s own employed teams rather than a nationwide contractor network
Verdict: For any project where a sizing error, a glazing defect, or a hardware fault would cause serious disruption, such as a listed building renovation or a high-specification residential extension, a direct-employment model like Fabco’s removes the accountability gap that subcontractor chains create. Buyers willing to pay a premium for that structure get a measurably cleaner line of responsibility from 3D survey to aftercare call-out.
Getting steel windows and doors fitted correctly matters just as much as picking the right product. This is where many projects stumble – and where you’ll spot the real difference between companies with their own teams and those relying on outside contractors.
Survey
Fabco kicks off every job with a 3D laser site survey run by one of their own surveyors. No tape measures. No guesswork. This swap replaces the manual method that often causes sizing errors before fabrication even starts. The 3D scan locks in exact dimensions before any steel gets cut.
Fabrication and project management
After the survey, a dedicated project engineer takes the wheel. They shepherd the job from West Sussex manufacture straight through to final installation sign-off. One person, one contact, no handoffs where things slip between departments or contractors.
Every W20 and W20+ frame passes through quality checks. These cover weld integrity, surface prep, hot-dip galvanising to British Standards, and hardware fitment before it ships.
Installation and glazing
Fabco’s own installation fitters do the physical work, then in-house glazing engineers finish the wet-glazing using RAL colour-matched, UV-resistant silicone. For fire-rated W40 FD30 doors, mechanically fixed steel glazing beads hold the fire-rated glass inside the tested Warringtonfire configuration.
Aftercare
After installation, a dedicated Customer Service Team handles follow-up support. Onsite Customer Service Engineers attend for both warranty and non-warranty call-outs. That’s a different level of service than a general phone line.
Frequently Asked Questions: Steel Windows, Installation & Aftercare
Steel windows and doors raise a lot of questions, especially around energy performance, fire ratings, and what happens after installation. Here are honest answers to the ones that come up most often.
What U-value do Fabco steel windows achieve?
It depends on the system. The standard W20 achieves a whole-window U-value of approximately 2.0 W/m²K with slimline 18mm double glazing (4mm outer pane, 10mm krypton-filled cavity, 4mm inner pane) and earns a B Window Energy Rating. The W20+ system hits 1.3 W/m²K on fixed lights and 1.4 W/m²K on opening windows and doors, earning an A+ rating. That’s a big jump from traditional single-glazed steel, which typically runs at 5.0 W/m²K or higher.
Do Fabco windows meet Building Regulations Part L?
Yes, though the route matters. The W20 meets current Part L for replacement windows via the Window Energy Rating route, using its B rating. It does not meet Part L via the U-value route because 2.0 W/m²K exceeds the 1.4 W/m²K limit. The W20+ satisfies both routes, with U-values of 1.3 to 1.4 W/m²K comfortably exceeding the threshold.
What fire rating does the W40 system carry?
Fabco’s W40 system is independently assessed by Warringtonfire for FD30 performance, meaning up to 30 minutes of fire resistance on one side. The assessment covers doors and screens within the Ottostumm steel doorset and screen configuration. It provides integrity only, not insulation, so it’s not an FD30S rating.
How does Fabco measure windows before fabrication?
Fabco uses state-of-the-art 3D laser site surveys carried out by directly employed surveyors. This replaces manual measuring, which is a common source of sizing errors. Exact dimensions are locked in before any steel is cut at the West Sussex manufacturing facility.
Are Fabco windows suitable for listed buildings and conservation areas?
Yes. The W20 system uses hot-rolled steel profiles with 10mm sightlines and a 32mm face width, closely matching the proportions of original early twentieth-century steel windows, many of which are still in service today. The system accepts single glazing for applications where planning or conservation officers require it, alongside slimline double glazing where thermal upgrades are permitted.
What security specification is available?
Standard doors come with a 5-lever mortice lock with drop bolts. A PAS 24 compliant specification is available as an upgrade, adding enhanced multipoint locking, security-tested hardware, and laminated security glass. Laminated glass stays in one piece when broken thanks to an interlayer that bonds multiple layers together, while toughened safety glass is up to five times stronger than standard float glass.
What happens if something goes wrong after installation?
Fabco has a dedicated in-house Customer Service Team and onsite Customer Service Engineers who handle both warranty and non-warranty call-outs. Because Fabco employs its own surveyors, fitters, and glazing engineers rather than subcontractors, there’s a single point of accountability rather than a chain of third parties to navigate.
Picking a steel glazing supplier involves more than comparing price quotes.
Work through these steps before committing.
1. Audit the fabrication spec sheet. Ask for sightline dimensions, U-values, and welding method in writing. A W20 system should show a 10mm sightline and a face width of 32mm. Thermal performance matters too – it should be confirmed against Part L. A B-rated WER (≈2.0 W/m²K) meets the rating route, while an A+ rating (1.3–1.4 W/m²K) exceeds it.
2. Verify who installs. This is straightforward: ask whether surveyors, fitters, and glazing engineers are employed or subcontracted. Fabco employs all of these in-house, which matters when something needs resolving post-installation.
3. Check fire-door credentials. FD30 doors should carry an independent assessment. Fabco’s W40 system is assessed by Warringtonfire.
4. Request aftercare terms in writing. Find out whether call-outs cover non-warranty faults and whether on-site engineers respond directly.
5. Review case studies relevant to your project type. Heritage, new-build, and commercial projects have different compliance requirements.
