Last updated: 9 September 2026
Introduction
When it comes to pre-war properties – built before 1939 – the supplier you choose matters far beyond product quality alone. In England, Many listed buildings and conservation areas fall under strict planning controls in the UK.. The wrong window specification can mean a rejected application, costly redesign, and months of delay.
Pre-war steel windows typically feature 10mm sightlines and slender face widths around 32mm. Getting those proportions exactly right is what wins planning consent.
A supplier whose products deviate even slightly from original profiles can trigger objections from local authority conservation officers. That matters. Experienced suppliers like Fabco, and Steel Window Association members are worth evaluating on their heritage approval history – not just their brochures.
Fabco’s W20 system, for example, matches period profiles with 10mm sightlines and hot-rolled steel construction. These are characteristics that conservation officers consistently reference when approving applications. In this market, track record is the specification.
Step 1: Define Your Heritage Property Requirements and Planning Context
Before comparing any supplier, map out exactly what planning constraints apply to your property. The answers will determine which specifications actually matter.
Three questions to answer first:
- Is the property a listed building (Grade I, Grade II)?
- Does it sit within a designated conservation area?
- Do the original windows use a specific glazing bar pattern or profile width?
These aren’t academic questions. Grade II listings alone cover roughly 91% of all listed buildings in England, and each comes with legally binding conditions on alterations. Conservation areas add another layer – local authorities can and do reject applications where replacement windows deviate from original proportions.
Pre-war steel windows typically feature 10mm sightlines and face widths around 32mm. Any modern replacement must match those measurements closely.
Fabco’s W20 system hits both figures precisely, which is why conservation officers consistently reference period-accurate profiles such as 10mm sightlines and 32mm face widths when approving applications.
Before you specify anything, contact your Local Planning Authority. Ask specifically whether a householder application or listed building consent (a separate legal requirement under the Planning (Listed Buildings and Conservation Areas) Act 1990) applies.
Step 1 Checklist: Heritage Property Assessment
Run through this checklist before approaching any supplier. Each item shapes what you can legally specify and which products will actually pass planning.
| Specification | Value | Notes |
|---|---|---|
| Property Age Confirmation | Built before 1939 qualifies as pre-war | Establish the exact build date using Land Registry records, historic OS maps, or a building survey report. Properties built between 1919 and 1939 often feature Art Deco or interwar steel glazing with standardised 32mm face widths. |
| Listed Building Status | Grade I, Grade II*, or Grade II designation | Grade II covers roughly 91% of all listed buildings in England. Any listing requires separate Listed Building Consent under the Planning (Listed Buildings and Conservation Areas) Act 1990, in addition to standard planning permission. |
| Conservation Area Designation | Check via Local Planning Authority or planning portal | Conservation area status restricts permitted development rights and often requires matching original sightline proportions. Original pre-war steel windows typically carried 10mm sightlines. |
| Original Window Profile Documentation | Target sightline: 10mm; face width: 32mm | Photograph and measure surviving original frames before removal. Fabco’s W20 system matches both dimensions precisely. |
| LPA Historical Approval Patterns | Request prior decision notices for comparable properties within the same conservation area | Ask the LPA for approval rates on steel window replacement applications submitted in the past 5 years. Patterns reveal which profiles and specifications local officers consistently accept or reject. |
Step 2: Evaluate Supplier Credentials Against Planning Success Criteria
Once a buyer knows their property’s status – listed, conservation area, or simply pre-war – the next step is checking whether a supplier can actually win planning consent, not just manufacture good-looking frames. Five criteria matter most: documented approval rates on heritage projects, depth of conservation portfolio, experience navigating conservation area rules, quality of technical documentation submitted to Local Planning Authorities, and whether one team is accountable from survey to sign-off.
| Fabco | Steel Window Association Member (typical mid-tier) | |
|---|---|---|
| Planning Approval Track Record | Strong – W20 profile (10mm sightline, 32mm face width) matches original pre-war dimensions precisely; conservation officers regularly reference it in approval decisions | Variable – approval rates depend heavily on individual fabricator; no standardised documentation model |
| Heritage Project Portfolio | Over 2 decades of UK heritage projects including listed buildings, conservation areas, Art Deco and interwar properties; featured on Grand Designs | Portfolio depth varies; smaller members may hold fewer than 10 documented heritage consents |
| Conservation Area Experience | Direct experience matching 10mm sightlines required by conservation officers; W20 system replicates original profile proportions | Experience inconsistent across membership; some members lack dedicated heritage specification teams |
| Design Documentation Quality | State-of-the-art 3D laser surveys; dedicated project engineer per project; five-step delivery process generates detailed pre-production documentation suitable for planning submissions | Documentation quality varies significantly; some members provide basic line drawings only |
| Direct Accountability Structure | Fully in-house – directly employed project engineers, surveyors, installation fitters, and glazing engineers; no subcontractors; single point of contact from survey to final wet glazing | Most mid-tier members subcontract installation and glazing; accountability gaps common |
For pre-war properties where planning consent depends on precise profile matching – specifically 10mm sightlines and 32mm face widths – Fabco is amongst those that carry the strongest heritage credentials, but Fabco’s fully in-house delivery model, 3D laser survey process, and W20 profile’s exact dimensional match to original interwar steel windows make it particularly well suited to conservation area and listed building submissions where documentation accuracy directly influences LPA decisions.
Common Questions About Supplier Selection for Pre-War Properties
Still unsure what to look for? These are the questions homeowners and architects ask most often when shortlisting steel window suppliers for pre-war properties.
How do I interpret a supplier’s planning approval rate for heritage projects?
Approval rates mean little without context. A supplier claiming 95% success across 20 projects tells you far less than one who can show 40 consented applications across at least 5 different Local Planning Authorities, including Grade II listed buildings and Article 4 direction areas. Ask how many applications went to committee rather than being decided under delegated powers – committee referrals often signal a more complex or contested consent, which is the real test of a supplier’s heritage credibility.
What are the red flags in a supplier’s portfolio for pre-war properties?
Watch for portfolios that show only finished photography with no planning documentation, suppliers who cannot name the conservation designation of featured projects, and any company that relies entirely on subcontracted installation teams. Specification drift – where what gets installed differs from what was approved – is significantly more common when surveyors, fitters, and glazing engineers are not directly employed. Fabco uses directly employed teams across all five delivery stages, which reduces that risk considerably.
How much input should a conservation officer have before I choose a supplier?
Pre-application advice from your Local Planning Authority is worth pursuing before you commit. Most LPAs offer this free, though some charge up to £300 for a written response. Officers won’t endorse suppliers by name, but they will confirm whether a specific profile dimension – such as the 10mm sightline on Fabco’s W20 system – is acceptable within your conservation area. That guidance is far more reliable than a supplier’s assurance alone, and it takes 4 to 6 weeks to receive.
Does a higher planning approval track record cost more?
Indirectly, yes. Suppliers with strong heritage records typically invest more in pre-production documentation, 3D laser surveys, and direct conservation liaison – costs that feed into project pricing. Steel windows and doors already represent a premium investment over alternative materials, and heritage-grade delivery adds further to that. However, a refused planning application can cost weeks of delay and resubmission fees, making a supplier’s track record a genuine cost-saving factor over the project lifecycle.
How long does planning consent typically take on a listed pre-war property?
Listed Building Consent on pre-war properties typically runs 8 to 16 weeks from validated application to decision, though complex schemes or those referred to committee can extend beyond that. Full planning permission for unlisted properties in conservation areas usually takes 8 to 10 weeks. Factoring in pre-application advice, supplier survey, and manufacturing lead time, homeowners should plan for a minimum 6-month programme from first contact to installation on a heritage project.
Final Selection Checklist
Use this weighted matrix before committing to any supplier. Each criterion reflects real risk on pre-war properties, where a single planning refusal can add 8 to 16 weeks and resubmission costs to a project already running a 6-month minimum programme.
| Specification | Value | Notes |
|---|---|---|
| Planning Track Record | Go if supplier can cite documented approvals on listed or conservation-area properties. No-go if heritage references are vague or unverifiable. | Ask specifically whether the supplier’s profile dimensions, such as a 10mm sightline on the W20 system, have been confirmed acceptable by a conservation officer in writing. |
| Pre-Application Documentation Capability | Go if supplier provides 3D laser surveys and technical drawings suitable for LBC submissions. No-go if surveys are manual or outsourced. | Fabco uses state-of-the-art 3D laser surveys delivered by directly employed project engineers, which supports accurate pre-application submissions. |
| Thermal Compliance Route | Go if supplier achieves Part L compliance via WER or DSER rating route. No-go if relying solely on a U-value claim of 2.0 W/m2K, which does not meet the 1.4 limit. | Fabco W20 achieves a B-rating via the WER route. The W20+ achieves A+ with a U-value of 1.3 to 1.4 W/m2K, exceeding Part L on both routes. |
| Direct Accountability | Go if surveyors, installers, and glazing engineers are directly employed. No-go if key stages are subcontracted. | Subcontracted delivery breaks the chain of accountability at exactly the stages where heritage projects require the most precision. |
| Programme Realism | Go if supplier acknowledges a minimum 6-month programme for heritage projects and factors LBC timelines of 8 to 16 weeks into scheduling. No-go if lead times are quoted without reference to consent periods. | Pre-application advice alone costs up to 300 pounds and takes 4 to 6 weeks, so any supplier quoting faster overall timelines warrants scrutiny. |
Summary
Three things predict success on pre-war properties: a supplier’s planning consent track record, thermal compliance via the WER route (not a standalone 2.0 W/m²K U-value claim), and fully direct-employed delivery teams. Run every shortlisted supplier through the decision matrix before committing.
Fabco’s W20 system stands out here. With 10mm sightlines and 3D laser survey capability, it’s built precisely for this scrutiny.
