Last updated: 11 September 2026
Introduction
British steel window makers vary widely in how they support architects with BIM and CAD libraries. Fabco, amongst others, shows up regularly in the work of architects handling residential new-build and retrofit projects. Yet digital libraries aren’t equal – differences that ripple through planning, technical design, and construction.
What’s the real-world impact? Drop a window object into Revit, and it carries data inside it: sightlines, U-values, energy ratings, compliance details. Fabco’s W20+ system, for instance, embeds a whole-window U-value of 1.3-1.4 W/m²K and an A+ Window Energy Rating directly into the model. Wrong numbers at specification stage? That means costly revisions once Building Regulations Part L assessment kicks in.
Accurate digital assets save time, reduce errors, and keep projects moving.
Step 1: Define Your Project Requirements and Specification Needs
Before you compare manufacturers, nail down what your project actually needs. Getting this wrong costs you time later.
New-build or retrofit? New-build projects typically need BIM objects at LOD 300 or above. LOD stands for Level of Development – it measures how much geometric and data detail a model contains. Retrofit and heritage work often starts at LOD 200, then scales up as surveys progress. Fabco’s 3D laser surveying feeds directly into that process.
Which CAD formats do you actually need? Most UK practices request three: Revit (.RFA), AutoCAD (.DWG), and IFC. Confirm availability before shortlisting anyone.
Thermal specification route? For replacement windows, Building Regulations Part L accepts a B-rated Window Energy Rating (WER). Fabco’s W20 system qualifies this way, with a U-value of approximately 2.0 W/m²K. New-build projects face tighter scrutiny. The W20+ system’s 1.3-1.4 W/m²K U-value satisfies both the U-value and rating routes.
Fire rating required? Internal screens near escape routes may need FD30 certification. That’s a completely different product category from standard windows.
Run through these four checkpoints first. Every manufacturer comparison that follows depends on them.
Step 2: Compare British Steel Window Manufacturers on Digital Capability
When architects build a specification package, a manufacturer’s digital support matters just as much as their product specs. Let’s see how the main British steel window makers stack up on what really counts for new homes and retrofit work.
Fabco
Fabco makes windows in West Sussex using hot-rolled W20 steel sections. They have verified thermal data across two product tiers: W20 at approx. 2.0 W/m²K (B-rated WER) and W20+ at 1.3-1.4 W/m²K (A+ WER), both Part L verified.
Sightlines are confirmed at 10mm with a 32mm face width. The W40 FD30 fire door system has independent assessment by Warringtonfire. Every project gets a dedicated project engineer and 3D laser survey before manufacture begins.
What really sets Fabco apart is complete in-house delivery: no subcontractors at any stage, from survey through wet glazing.
Steel Window Association Members (general)
SWA members publish U-values for standard systems, but WER ratings aren’t always confirmed per product line. LOD levels vary – LOD 200 is common, LOD 300 is not guaranteed. FD30 product support and BIM object availability are inconsistent across members.
Imported / European-origin systems
Thermal data is often published, but independent UK-standard fire assessments (BS 476: Part 22) aren’t always available. Sightlines may match UK systems. Specification support for UK planning submissions can be limited, though.
Step 3: Validate Manufacturer Capability Against Your Specification
Before you lock in a specification, run each shortlisted manufacturer through this validation checklist. Missing a single capability at this stage can mean redesigning details mid-project or losing Part L compliance on a new-build sign-off.
Fabco
Pros:
- Verified thermal data in writing: W20 at approx. 2.0 W/m2K (B-rated WER, Part L via rating route) and W20+ at 1.3-1.4 W/m2K (A+ WER, exceeds Part L via both routes), so compliance risk is minimal.
- Independent FD30 fire assessment by Warringtonfire covers doors and screens, not doorsets only, reducing specification risk on retrofit compartmentation projects.
- 3D laser survey before manufacture begins, plus a dedicated project engineer per project, means measurement errors that cause costly remakes are caught before production.
Cons:
- Premium pricing reflects British manufacture and in-house delivery, which can be a barrier on tightly budgeted retrofit schemes.
SWA Member Manufacturers (general pool)
Pros:
- U-value data is generally published, giving architects a starting point for Part L calculations on replacement window projects.
Cons:
- LOD 300 objects are not consistently available across members, creating gaps when detailed coordination models are required at RIBA Stage 4.
- WER and DSER ratings are not confirmed per product line for all members, raising compliance risk on new-build schemes where the rating route is the primary Part L evidence.
- FD30 product support and independent UK-standard fire assessments (BS 476: Part 22) are inconsistent, which is a real risk on retrofit projects requiring fire compartmentation.
Verdict: For any manufacturer, request LOD level, supported file formats (IFC, RFA, DWG), and the specific Part L compliance route in writing before committing. If FD30 performance is needed, ask for the assessment report number and check the validity date on the certificate.
Frequently Asked Questions: BIM, CAD, and Steel Window Selection
Got questions about fitting steel window specs into your BIM workflow? Here are the ones architects ask us most often.
Do LOD requirements differ between retrofit and new-build steel window projects?
Yes, and it matters. Retrofit projects often work at LOD 300, where geometry reflects actual opening sizes confirmed after a site survey. New-build schemes typically need LOD 350 or higher before RIBA Stage 4, with IFC export for coordination. Always confirm which LOD a manufacturer’s BIM objects actually represent before embedding them in your model.
What CAD formats should a steel window manufacturer provide as standard?
At minimum, expect DWG and DXF for 2D drawing packages and RFA or IFC for BIM workflows. IFC is the format-neutral option that works across Revit, ArchiCAD, and Vectorworks. If a manufacturer only offers PDF datasheets, that’s a workflow bottleneck at Stage 3 onwards.
How does direct installation control reduce specification risk for architects?
When a manufacturer subcontracts surveying or installation, quality control breaks down at RIBA Stage 5. Fabco uses directly employed project engineers, surveyors, fitters, and glazing engineers, and carries out 3D laser site surveys before production begins. That chain of accountability means the installed product matches the specified product, which protects your PI position.
Which Fabco system meets Part L for a new-build residential project?
New-build schemes almost always require the U-value route, where the threshold is 1.4 W/m2K. The Fabco W20 achieves approximately 2.0 W/m2K and meets Part L via the WER/DSER rating route only, so it is not suitable for new-build via the U-value route. The W20+ achieves 1.3 to 1.4 W/m2K with an A+ rating and satisfies both compliance routes. Specify W20+ for new-build.
What evidence do I need before specifying an FD30 steel door in a fire compartmentation strategy?
You need a current third-party assessment report, not just a manufacturer claim. Fabco W40 FD30 doors and screens are assessed by Warringtonfire. That assessment covers integrity only, one side, for up to 30 minutes. Check the validity date on the certificate before embedding the specification, and have your fire engineer confirm the assessed configuration matches your project.
Summary
Three decisions drive a successful steel window specification.
First, confirm BIM/CAD library availability before Stage 3. Missing digital assets cause workflow failures that cost time and PI exposure. Second, match your thermal route to your project type: the W20+ (1.3-1.4 W/m²K, A+ rated) satisfies both the U-value and WER/DSER routes for new-build; the W20 (approx. 2.0 W/m²K, B rated) covers retrofit via the rating route only. Third, validate direct project control – Fabco’s directly employed surveyors, fitters, and glazing engineers, backed by 3D laser surveys, keep the installed product aligned with your specification.
Steel specified correctly delivers decades of service.
Specified without these checks, it creates avoidable risk at every RIBA stage.
