Steel-Look and Aluminium Doors in Streatham Hill and Brixton (SW2)

Streatham Hill and Brixton (SW2) are among Direct Trade Windows’ busiest London postcodes: 14 orders since May 2022, most of them steel-look aluminium doors and windows in matt jet black. Here we cover what Lambeth’s planning guidance asks for, how a rear extension should sit on a Victorian terrace, and which door system suits which house.

Why does SW2 suit steel-look glazing?

SW2 is Victorian and Edwardian terraces standing next to some of south London’s finest 1930s mansion blocks, many still fitted with their original metal casements. That makes the black, slim steel-window look part of the local architecture rather than an import. It is at home on a period rear extension because the street already has it.

Lambeth’s own conservation documents set this out. The Streatham High Road and Streatham Hill Conservation Area statement describes Corner Fielde (1937) as having “Crittall type metal casements with opening top lights to allow maximum light into the flats”. Wavertree Court (1933) and The High (opened 1937) also have Crittall-type metal casements, and at Manor Court (circa 1935) “the original Crittall type windows are painted black throughout the complex”.

A mile north, the Rush Common and Brixton Hill Conservation Area appraisal lists five 1930s apartment buildings along Brixton Hill. Among them are Dumbarton Court (1939), whose “original wrap around Crittall windows” the council singles out, and Christchurch House (1938), with its curving white balconies and Crittall windows. Behind these main roads are the Victorian and Edwardian terraces where most of our SW2 work actually happens. Nearby Telford Park is a conservation area of its own: Queen Anne-style houses designed by E. J. Tarver and laid out between 1878 and 1882.

A homeowner here isn’t choosing between “modern” and “period”. Both are already on the street. The job is to pick the version that still looks right on the house in twenty years.

What have we installed in SW2?

Our order book holds 14 SW2 orders from May 2022 to September 2026, across 11 separate postcodes in four postcode sectors (SW2 2, 3, 4 and 5). Seven of the eight orders placed since 2024 include Smart Alitherm Heritage steel-look doors or windows. Of the ten orders with a colour recorded, eight are jet black RAL 9005 matt.

By Lambeth ward (from each order’s postcode), the work breaks down like this:

The photograph at the top of this page is one of the Streatham Hill East jobs, completed in May 2026: two steel-look openings across the back of a Victorian terrace, separated by a brick pier. On the right is a pair of French doors between two fixed side panels. On the left is a second glazed screen with a matching grid of glazing bars. Both are in matt jet black.

Do you need planning permission to replace windows or doors in Streatham Hill or Brixton?

For a house, replacing windows and doors is usually permitted development if the new ones look similar to the originals. A flat needs planning permission whenever the design, opening method, materials or profile change. A listed building always needs listed building consent. Conservation areas bring extra scrutiny.

1. Houses. The Planning Portal’s rule is that permitted development covers “new windows and doors that are of a similar appearance to those used in the construction of the house”. A new bay counts as an extension. An Article 4 direction can remove these rights, so check the address before relying on them.
2. Flats, including every mansion block above. Lambeth says a like-for-like replacement needs no permission. But “if the design, method of opening, materials and profile of the replacement windows are not the same as the existing windows, then planning permission will normally be required.”
3. Listed buildings. Listed building consent is needed on top of anything else.
4. Conservation areas. SW2 includes all or part of Rush Common and Brixton Hill, Streatham High Road and Streatham Hill, Telford Park and Brixton Water Lane. Lambeth’s Design Guide (Part 4, para 4.17) says replacement windows on heritage assets and in conservation areas should have integral glazing bars rather than stick-on ones, should avoid obtrusive trickle vents, and should be “of the same material as the original windows”.

Steel-look aluminium is made to meet the first two of those conservation-area requirements. Our glazing bars are structural parts of the frame, not stick-on strips. The third requirement, same material, is a real limit, and the next section deals with it honestly.

Can steel-look aluminium replace original metal windows in a mansion block?

Sometimes, but it isn’t a shortcut. Swapping original steel windows for aluminium in a flat is a change of material, so Lambeth will normally want a planning application. In a conservation area its design guide expects the original material. For original windows in good condition, repair or specialist steel replacement is often the right answer.

We would rather say that plainly than sell the wrong window. Lambeth’s design guide points owners of heritage assets to Historic England’s guidance on caring for and repairing traditional windows, and that guidance puts repair first. Aluminium has a stronger case where the originals have already been lost to earlier replacements, where the building is outside a conservation area, or on elevations the public doesn’t see. Whether a particular block falls into one of those cases depends on its planning history, its lease and its managing agent. We are happy to look at that with you before anyone talks about a quote.

The steel-look system we fabricate, Smart’s Alitherm Heritage, is described by its manufacturer as “designed as a direct replacement for steel windows”. It is a thermally broken aluminium system. That is the practical difference from original single-glazed steel: it takes double or triple glazing and doesn’t carry the condensation and rust that old steel frames do.

What does Lambeth want from a glazed rear extension on a Victorian terrace?

Lambeth accepts glazed rear extensions but dislikes one long, uninterrupted band of glass across a period house. In conservation areas it resists full-width wrap-around glazing and suggests stepping the façade or setting brick piers between the glazed openings. Steel-look glazing bars do the same job at the scale of the frame.

The design guide is specific. Wrap-around extensions “will be resisted on heritage assets and buildings in conservation areas as the horizontal emphasis and dominance of glazing is not considered a sympathetic response” (para 4.56). For full-width boxes on stepped rear elevations, it says “stepping the façade and introducing brick piers between the glazing” helps reduce that effect (para 4.59). Mostly glazed infill extensions are its preferred approach, because they leave the original rear return looking like the main building (para 4.55).

The Streatham Hill East job at the top of this page shows what that looks like in practice. The glazing is split into two openings with brickwork between them, and each opening is divided by bars into panes about the size of the house’s own windows. From the garden it reads as part of a Victorian house, not a glass box added to the back of one.

Steel-look, sliding or bifold: which suits an SW2 rear?

Choose steel-look where the house has period character and the opening is a normal door width. Choose a slim-frame sliding door where the aim is the widest, least interrupted view of the garden. Bifolds suit openings where fully clearing the gap in summer matters more than the view when closed. We fit all three in SW2.

One more practical point. Steel-look doors taller than 2200mm get a fanlight above for the rest of the height, which is how original steel doors were built. On a Victorian rear with a high ceiling line, that is usually the more convincing choice anyway.

Can you fit steel-look doors in a loft dormer?

Yes, and it’s a good fit for SW2’s loft conversions. Lambeth’s design guide says dormers containing a glazed door and a Juliet balcony should only go on rear elevations. In its advice on roof extensions, it also asks that dormer windows line up with, and match, the windows on the floor below.

The dormer above is from one of our Brixton Acre Lane orders, which combined steel-look doors and windows. Using the same black frames and bar pattern throughout makes the back of the house read as one piece, which is the consistency Lambeth’s guidance asks for. It also makes a clear case to a planning officer.

What does the Alitherm Heritage system actually deliver?

Smart publishes these figures. Alitherm Heritage windows have a 47mm frame, 59mm typical sightlines and a U-value of 1.6 W/m²K with a 1.0 W/m²K glass unit, and are tested to PAS 24. Heritage 60 doors reach 1.4 W/m²K double-glazed or 1.1 W/m²K triple-glazed.

We fabricate the system ourselves in our Slough factory and install it across the country. SW2 is our second-busiest London postcode after SW19. That volume is useful to you: our survey team already knows how London stock-brick reveals, Victorian rear returns and slate-hung dormers behave when a frame goes in.

Sources: Lambeth Council, Design Guide SPD Part 4; Streatham High Road and Streatham Hill Conservation Area statement; Rush Common and Brixton Hill appraisal; Telford Park conservation area; Replacing windows in a flat; Planning Portal: doors and windows; Smart Systems, Alitherm Heritage and Alitherm Heritage 60. Install figures come from Direct Trade Windows’ own order records; ward names are from ONS postcode data.