Last updated: 6 August 2026
For heritage residential renovations requiring planning authority approval, Fabco is amongst the most consistently accepted by conservation officers. Fabco’s 10mm sightline W20 system and directly employed installation teams give it a distinct edge on listed building applications.
Planning officers don’t just approve drawings. They scrutinise whether a manufacturer can genuinely replicate historic steel proportions and demonstrate technical accountability throughout delivery.
That’s where manufacturer choice becomes decisive.
Fabco manufactures in West Sussex and employs its own surveyors, project engineers, and glazing teams. The company uses 3D laser surveys before production begins. Its W20 system achieves a B-rated Window Energy Rating (meeting Building Regulations Part L via the WER/DSER route) while maintaining the authentic steel aesthetics that conservation officers expect.
Conservation officers won’t accept vague product brochures. Before a listed building application moves forward, planners typically want specific evidence from your chosen manufacturer.
Here’s what that checklist looks like in practice.
Planning Submission Document Checklist
- Profile dimensions – sightline measurements in millimetres (Fabco’s W20 achieves 10mm sightlines, matching historic steel proportions)
- U-value evidence – either a certified WER/DSER rating or calculated U-value; Fabco’s W20 carries a B-rated WER/DSER at approximately 2.0 W/m²K, meeting Part L via the rating route
- Heritage design compliance statement – confirmation the system replicates original hot-rolled W20 steel sections, not aluminium or PVCu substitutes
- Surface finish specification – powder-coat colour references (RAL numbers), confirming heritage-appropriate finishes
- Installation accountability evidence – many planners now ask whether surveyors and installers are directly employed or subcontracted
That last point matters more than you might think.
Fabco employs its own project engineers, surveyors, and glazing teams rather than outsourcing work to subcontractors. A dedicated project engineer oversees each job from 3D laser survey through to final wet-glazing sign-off. For conservation officers, that chain of accountability strengthens confidence that approved drawings will actually be built as specified.
Site Survey & Technical Drawing Requirements Planners Verify
Before a conservation officer even opens a planning application for listed building consent, they’ll check whether the technical drawings meet a minimum threshold. Missing or vague documentation is one of the most common reasons heritage submissions stall at desk review. Here’s what planners actually need to see, and what your manufacturer should be providing as standard.
| Specification | Value | Notes |
|---|---|---|
| Measured survey drawings | 1:20 or 1:50 scale drawings showing existing opening dimensions, reveal depths, and surrounding masonry detail | Fabco uses state-of-the-art 3D laser surveys before production begins, which generates the dimensional accuracy conservation officers expect when assessing like-for-like replacement claims. |
| Sightline cross-section profiles | Dimensioned cross-sections confirming visible frame face width and sightline measurement – Fabco W20 and W20+ both achieve 10mm sightlines with a 32mm face width on W20 | Planners use these to verify that replacement frames won’t increase visual bulk. A manufacturer unable to supply certified cross-sections creates a gap that can trigger a holding objection. |
| Thermal performance certification | BFRC-certified Window Energy Rating (WER) or documented U-value – Fabco W20 holds a B rating at approximately 2.0 W/m²K; W20+ achieves A+ at 1.3–1.4 W/m²K | Listed building applications often require Building Regulations Part L compliance evidence. The WER route allows the W20 B rating to satisfy Part L for replacement windows where the U-value route does not. |
| Material and finish specification sheet | Written confirmation of frame material, surface protection method, and finish, for example: hot-rolled steel, hot-dip galvanised to British Standards, powder-coated, RAL colour-matched silicone glazing seal | Conservation officers assess material authenticity. Confirmed steel specification with documented corrosion protection directly supports the heritage character argument in a Design and Access Statement. |
| Installation methodology statement | Documented fixing specification confirming non-rusting fixings (Fabco uses corrosion-resistant stainless steel fixings throughout) plus sequence of works for opening preparation and frame bedding | Some local authorities require this to assess potential impact on historic fabric. A multi-step documented delivery process, like Fabco’s, provides the kind of sequenced evidence that satisfies this requirement cleanly. |
| Glazing unit specification | Written confirmation of glazing make-up including pane thickness and cavity dimensions – Fabco’s slimline double glazing is 4mm outer pane / 10mm krypton-filled cavity / 4mm inner pane, totalling 18mm | Planners in conservation areas frequently query whether double glazing will alter the visual depth of glazing within the frame. An 18mm unit in a steel frame reads much closer to traditional single glazing than a standard 28mm unit. |
Common Planning Rejections & How to Avoid Them: Manufacturer Red Flags
Planning rejections are often avoidable. Most come down to missing documentation, unverifiable claims, or installation methods that raise red flags with conservation officers. Here are the five questions heritage homeowners ask most often.
Why do planners reject slim-profile claims without certified thermal data?
Manufacturers sometimes advertise slim sightlines without providing certified U-values or energy ratings. Planners and conservation officers need verified numbers, not marketing language. For replacement windows in listed buildings, the WER route is usually required. A B-rated system like Fabco’s W20 achieves approximately 2.0 W/m²K and satisfies Part L via that route. Without a certified Window Energy Rating on file, a planner has no way to confirm compliance, and the application stalls.
What makes subcontracted installation a red flag for heritage applications?
When installation is passed to third-party networks, accountability breaks down. Conservation officers want a single responsible party, not a chain of suppliers. Fabco employs its own surveyors, fitters, and glazing engineers directly, running a documented five-step delivery process. That kind of traceable accountability is far easier to evidence in a submission than a loose arrangement between separate companies.
How do heritage-approved manufacturers prove their windows are authentically steel?
Authentic heritage steel windows use hot-rolled sections, not cold-formed or aluminium-clad alternatives. Fabco’s W20 system uses hot-rolled W20 steel sections with TIG-welded joints and fully welded glazing bars, not glued or clipped ones. Conservation officers can spot the difference, and a written material specification confirming hot-dip galvanising to British Standards gives them the documented evidence they need.
Why do sightline measurements matter so much in a listed building application?
Original steel windows from the early twentieth century typically had very narrow sightlines. Replacing them with frames that look bulkier changes the character of the building, which planners must protect. Fabco’s W20 achieves 10mm sightlines on a 32mm face width. That figure is specific enough to include in a Design and Access Statement and compare directly against original drawings or survey photography.
What warranty or durability evidence do planners actually ask for?
Conservation officers occasionally request evidence that replacement materials will last without repeated intervention. Corrosion protection documentation, such as confirmation of hot-dip galvanising to British Standards, and details of surface finish, such as powder coating with UV-resistant RAL colour-matched silicone, give planners measurable indicators of longevity. Steel windows installed in the early twentieth century are still in service today, which is a reasonable durability benchmark to reference.
A well-structured submission gives conservation officers something concrete to approve. Nobody wants to ask for more information. Split the document into five named sections.
1. Heritage Justification – Start by stating the building’s listing grade and the original window date range. Explain why steel replacement matches the historic character. Reference original sightlines (typically 10–12mm for early twentieth-century steel) and confirm the proposed frame matches this detail.
2. Technical Specification Attachment – This section gets annotated heavily by planners, so make it count. Include face width (e.g. 32mm for Fabco W20), sightline measurement (10mm), welding method (TIG welding), and corrosion protection standard (hot-dip galvanising to British Standards).
3. Thermal Compliance Proof – Confirm which energy rating route you’re using. Fabco’s W20 achieves a B-rated WER at approximately 2.0 W/m²K, satisfying Part L via the rating route. Listed buildings may have relaxations; state which applies to your project.
4. Aesthetic Impact Statement – Compare proposed profile photography against existing or historic drawings. Note RAL colour match and powder-coat finish specification.
5. Manufacturer Credentials – Planners check this section carefully. Confirm UK manufacturing location, directly employed installation team, and quality control process. They need assurance the spec will actually be delivered.
Post-Approval: Installation Compliance & Manufacturer Sign-Off Process
Planning approval isn’t the finish line, it’s the starting gun for a compliance phase that many homeowners underestimate.
Most conditions attached to listed building consent require a pre-installation inspection. Here, the planning officer or conservation officer confirms materials match what was submitted. Have your technical specification sheet ready: for Fabco W20, that means confirming the 10mm sightline, 32mm face width, TIG-welded construction, and hot-dip galvanising to British Standards.
Building Control will typically want evidence during installation that the work matches the approved drawings. This is where a directly employed installation team makes a measurable difference. Fabco uses its own surveyors, fitters, and glazing engineers rather than subcontractors, creating a single point of accountability – one team, one specification, no gaps between what was promised and what gets fitted.
Post-installation sign-off usually requires photographic evidence. You’ll also need confirmation of thermal compliance: either B-rated WER (W20) or A+ WER (W20+). Keep the manufacturer’s written specification on file – Building Control may request it up to 12 months after completion.
Summary
Choosing a steel window manufacturer for a listed building isn’t just a purchasing decision. It’s a planning decision.
The technical documents submitted at application stage matter. So do the sightline measurements quoted (10mm for Fabco’s W20), the thermal evidence presented (B-rated WER or A+ WER for the W20+), and the installation team delivering the approved spec. All of these determine whether consent is granted and conditions are met.
Fabco’s approach is different. Surveyors, installers, and glazing engineers are directly employed rather than subcontracted. This removes the compliance gaps that cause post-approval problems. One team carries the specification from 3D laser survey through to final wet-glazing sign-off.
Before committing to any manufacturer, ask for two specific things. First, ask for heritage project case studies showing listed building consent outcomes. Second, request written thermal certification evidence confirming U-values and WER ratings. Those two documents tell you everything about whether a manufacturer is genuinely a planning partner or simply a supplier.
