Most homes across Barnet can take slim aluminium or steel-look replacement windows, but consent decides the detail. Barnet Council controls its conservation areas, and inside Hampstead Garden Suburb a separate Trust consent applies on top of council planning permission. Establish which regime covers your address before you specify a single frame.
The Barnet belt — East Finchley, Finchley, Whetstone, Totteridge and Hendon — is one of the most consistent bodies of inter-war and Edwardian housing in north London. It is also one of the most tightly controlled. We have delivered 31 orders into the N2, N3, N20 and NW4 postcode districts, and the single question that decides most of them is not which system to use. It is which permission you need.
Do you need planning permission to replace windows in Barnet?
For most Barnet houses outside a conservation area, replacing windows is permitted development and needs no planning application. Inside a conservation area, or where an Article 4 Direction has removed those rights, you need consent — and flats and maisonettes never had permitted development rights for windows in the first place.
Two of the areas covered here carry conservation designations made in the same year. Much of Totteridge (N20) was designated a conservation area in 1968, and no major development has taken place there since. Hampstead Garden Suburb, on the N2/NW11 boundary, was designated by Barnet Council in the same year, in recognition of what the council defines as “an area of special architectural or historic interest, the character or appearance of which it is desirable to preserve or enhance”.
Barnet has gone further than designation alone. As the council’s own guidance records, it “has also obtained extra powers to control many types of development that would not normally require planning permission by making an Article 4 Direction, which gives additional control over external alterations to properties or new building works”. Where that applies, the permitted development right you were relying on has been withdrawn.
| Your situation | Barnet Council planning | Suburb Trust consent |
|---|---|---|
| House outside a conservation area, like-for-like replacement | Usually permitted development — confirm before ordering | Not applicable |
| Flat or maisonette, anywhere in the borough | Planning permission required | Not applicable |
| House in a Barnet conservation area (e.g. Totteridge) | Consent required where an Article 4 Direction applies | Not applicable |
| Property inside the Hampstead Garden Suburb Scheme of Management | Required | Required, separately and in addition |
| Listed building, anywhere in the borough | Listed Building Consent required | Required if inside the Suburb |
What is the Hampstead Garden Suburb Scheme of Management?
The Hampstead Garden Suburb Trust controls external alterations under a Scheme of Management approved by the High Court under the Leasehold Reform Act 1967. It covers some 880 acres and over 5,000 properties. Trust consent is a separate legal requirement that sits alongside — not instead of — Barnet Council planning permission.
The Suburb was founded in 1906 by Henrietta Barnett, master-planned by Raymond Unwin with Barry Parker, with Sir Edwin Lutyens designing Central Square. The Trust’s present control derives from a scheme of management approved under the Leasehold Reform Act 1967 by an Order of the Chancery Division of the High Court dated 17 January 1974, amended by a further Order dated 17 February 1983.
The practical consequence is spelled out in the design guidance the Trust and Barnet Council publish jointly. Among the changes needing consent from both bodies is “changing windows, external doors, garage doors or gates, even in detail or material or colour“. That last clause is the one homeowners miss. Swapping a white frame for a black one, in the same opening, in the same material, is a change requiring consent.
Can you fit aluminium windows in Hampstead Garden Suburb?
Generally no, where you are replacing original steel windows. The Trust’s supplementary steel window guidance states that an existing steel window should be replaced with a steel window, and limits double glazing to 16mm overall. Aluminium steel-look systems cannot meet that unit depth, so they are the wrong product for a Suburb application.
We would rather say this plainly than sell you something that gets refused. The Trust’s supplementary guidance on steel windows is explicit: “Generally, an existing steel window should be replaced with a steel window.” It goes on to note that where originals have already been swapped for aluminium or plastic, those windows “usually fail to match the form and appearance of the originals and damage the character of the property”, and that the Trust would expect them to be put back to steel.
The specification detail settles it. The Trust “will usually allow double glazing up to a maximum overall depth of 16mm (4mm glass – 8mm gap – 4mm glass)”, with internal spacers matching the frame colour. A modern thermally broken aluminium steel-look system is built around a much deeper unit — our own steel-look range takes 28mm double or 44mm triple glazing. The arithmetic does not reconcile. The guidance also rules out visible trickle vents and friction hinges, and does not generally accept double-glazed leaded lights on front elevations.
So: if your property sits inside the Scheme of Management boundary and you are replacing original steel, you need a steel window specialist, not us. If it sits outside — and the great majority of Barnet does — aluminium steel-look is very often the right answer. The first job on any Barnet enquiry is establishing which side of that boundary you are on.
Which window system suits Barnet’s inter-war housing stock?
Inter-war Barnet houses were built with steel casements and timber sashes in strong vertical proportions. Steel-look aluminium replicates the first, aluminium vertical sliders the second, and slim sliding doors open up the rear without touching the street elevation. The choice usually follows which elevation is visible from the highway.
| System | Frame / sightline | Where it earns its place in Barnet | Published performance |
|---|---|---|---|
| Steel-look windows (Smart Alitherm Heritage 47) | 47mm frame depth, heritage sightlines | Replacing Crittall-era steel casements in 1920s–30s stock, and conservation-area applications outside the Suburb | U-value from 1.4 W/m²K double glazed, from 1.1 W/m²K triple; 28mm or 44mm units |
| Steel-look doors | Matched to the window range | Garden doors and internal screens where the grid needs to continue through the opening | Same system family and finishes as the windows |
| Cortizo Cor Vision sliding doors | 20mm sightline | Rear extensions where the glass should read as one uninterrupted plane | Interlock reduced to a single slim upright between panels |
| Cortizo Cor Vision Plus sliding doors | 25mm sightline | Larger rear openings carrying heavier panel weights | The same visual language at greater spans |
| Aluminium vertical sliders | Sash proportions in aluminium | Front elevations that must keep a sash rhythm where aluminium is permitted | Sash is a window style, not a material |
Colour tells its own story here. Of the 31 Barnet-belt orders, 13 record RAL 9005 matt black as the finish — more than every other named colour in those jobs combined. That is the inter-war palette reasserting itself: these houses were built with dark steel casements, and dark frames are what the architecture wants back.
Where we install across the Barnet belt
We hold 31 orders across the four Barnet-belt postcode districts: 12 in N2, seven in N3, seven in N20 and five in NW4. They run from 2022 to 2026 and cover steel-look windows and doors, Cortizo sliding doors, aluminium vertical sliders, bifolds and rooflights.
East Finchley (N2) — 12 orders
Our densest Barnet district. The housing is genuinely mixed: 19th-century terraces, substantial 1930s houses, and the very large properties of The Bishops Avenue. This is also where the Hampstead Garden Suburb boundary matters most — an N2 address tells you nothing about whether the Scheme of Management applies, so we check it before quoting rather than after. The steel-look screen pictured above is an N2 job.
Finchley and Church End (N3) — seven orders
Centred on Ballards Lane and Finchley Central station. Finchley grew hard after the railway arrived in 1867 — the population went from 11,191 in 1881 to 69,991 by 1951 — and the housing reflects each wave of that expansion. Rear extensions with slim sliding doors are the common brief here, because the street elevations are largely intact and worth leaving alone.
Whetstone and Totteridge (N20) — seven orders
Two quite different jobs sharing a postcode. Whetstone is inter-war semi-detached and detached stock — the houses in the photographs on this page. Totteridge is spacious detached property in a green setting, much of it inside the conservation area designated in 1968; Victorian and Edwardian houses went up around the old village after the station opened in 1872, with smaller housing near the tube from the late 1930s. Conservation status changes the conversation, so we start with it.
Hendon (NW4) — five orders
Hendon is the clearest inter-war case in the group. Hendon Central station opened in 1923, and in that year alone 687 houses were built with plans approved for 1,500 more. That produces street after street of houses of near-identical age and detailing — which is exactly the condition in which a badly proportioned replacement window is visible from fifty yards away, and a well-proportioned one disappears.
How does steel-look aluminium differ from original steel?
Original steel windows are single-glazed, uninsulated and putty-glazed, with sightlines of a few millimetres. Steel-look aluminium reproduces the visual grid and the dark finish while carrying a thermal break and a sealed double or triple unit. The frames are necessarily thicker; good detailing is what closes the gap.
Honesty about that difference is what separates a specification that survives a planning officer from one that does not. A 1930s steel casement was a thin rolled section holding a single pane in putty, set back behind a timber sub-frame. It looks the way it does because it had no insulation to accommodate. A steel-look aluminium window carries a polyamide thermal break and a sealed unit, so its sections are deeper.
What you can control is everything that reads from the street: the width and spacing of the glazing bars, the subdivision into fixed and opening lights, the set-back of the frame in the reveal, and the finish. Get those right and the replacement reads as correct. Get them wrong and no amount of performance data rescues it.
What to check before you specify windows in Barnet
- Establish your consent position first. Conservation area? Article 4 Direction? Listed? Inside the Hampstead Garden Suburb Scheme of Management? These are four separate questions with four separate answers.
- Photograph every existing window before anything is removed. Both Barnet Council and the Trust ask for exterior photographs of the existing windows as part of an application.
- Get the survey done in imperial-aware detail. Original openings in this stock are set out in imperial sizes, and a replacement that is slightly undersized ends up packed out with mortar or foam — visible, and refusable.
- Decide the glazing bar layout on drawings, not on site. Bar width, spacing and the fixed/opening split are what a conservation officer looks at.
- Allow for lead time. Bespoke frames take months, not weeks. Consent bodies will not accept a substandard window because a programme is tight.
We fabricate in our own factory in Slough and install nationwide; Barnet is one of the areas where our install record is deepest, not the limit of where we work. If you want the underlying consent documents, the Trust publishes its steel window guidance and the joint Hampstead Garden Suburb conservation area design guidance in full.
Planning a window or door replacement in Barnet?
Send us the address and a photograph of the existing windows. We will tell you which consents apply, which system suits the elevation — and, if it is a Suburb steel replacement, that it is not a job for us.
