Crittall style doors are slim-framed glazed doors divided by narrow glazing bars, reproducing the look of early twentieth-century steel windows in thermally broken aluminium. Modern versions carry bar faces from 25mm, published U-values from 1.4 W/m²K with double glazing, and multi-point locking — none of which the original single-glazed steel sections had.
Crittall® is a registered trademark of Crittall Windows Ltd, a steel window manufacturer trading since 1849. “Crittall style” describes an appearance — slim dark frames divided by glazing bars — not a product. Direct Trade Windows fabricates thermally broken aluminium doors in that style; we do not supply Crittall® product.
What are Crittall style doors, and what are they actually made of?
They are aluminium doors detailed to look like steel. The frame is an extruded aluminium profile with a polyamide thermal break running through it, finished in a dark powder coat or anodised finish, and divided by applied astragal bars into the grid that gives the style its name. The glazing is a sealed double or triple unit, not single glass.
That distinction matters more than the aesthetics. A period steel window is a solid section carrying single glass: it conducts heat straight through the frame and it corrodes. A steel look aluminium door reproduces the proportions while carrying a sealed unit and an insulating barrier through the middle of the profile. You get the look of the original without its heat loss, condensation or rust.
How slim can the glazing bars go — 25mm or 48mm?
Two bar widths cover almost every project. The 48mm section is the classic proportion and the one most widely specified for heritage renovations, because it reads at roughly the visual weight of an original steel section. A 25mm edge-cut bar gives a slimmer, more refined line and suits contemporary extensions where the grid is a design motif rather than a restoration.
Choose by what the elevation is doing. On a 1930s rear elevation being put back to something like its original rhythm, the 48mm bar is almost always right — a 25mm bar on a period house reads as a modern reference to the style rather than a continuation of it. On a new glass box off the back of a Victorian house, the 25mm bar carries the industrial language without pastiche.
Bar layout is worth as much attention as bar width. Squares that are visibly not square, or a horizontal that doesn’t line through from the door to the flanking screen, is the single most common way a steel look installation announces itself as a retrofit.
Which steel look system suits which opening?
Three system routes cover the range, and they are not interchangeable. Windows and screens sit on a 47mm platform, hinged and French doors on a 60mm one, and wide folding openings move to a Cortizo bifold profile with astragal bars applied. Frame depth rises with the load the opening has to carry.
| System | Frame depth | Glazing capacity | Published U-value | Typical use |
|---|---|---|---|---|
| Smart Alitherm Heritage 47 | 47mm | 28mm double / 44mm triple | From 1.4 W/m²K double, from 1.1 W/m²K triple | Windows, fixed lights, screens; fixed, side-hung, top-hung and tilt & turn |
| Smart Alitherm Heritage 60 | 60mm (48mm face width) | Up to 36mm | From 1.4 W/m²K double | Single and French doors, doors with sidelights or fanlights |
| Cortizo bifold with astragal bars | 73mm | Up to 48mm | Confirm per configuration | Wide folding openings — panels to 1200mm wide × 3000mm high, 120kg per leaf, up to 7 leaves per side |
The published performance data on our Crittall style doors range includes air permeability Class 4 (600Pa), watertightness to Class 8A (450Pa) opening outward, wind resistance Class 3 (1200Pa), testing to PAS 24:2016, compliance with BS 6375-1:2009 and BS 4873, and Kitemark certification. The Heritage 47 window platform publishes acoustic reduction up to 45dB. Ask for the certified figures for your exact configuration rather than the range headline — glazing make-up, size and opening type all move the number.
Two sizing rules are worth knowing before you draw anything. A single leaf on the classic door platform is published to a maximum of 900mm wide by 2100mm high. And any steel look product above 2200mm in height takes a fanlight above for the remaining height — that is a fabrication rule, not a preference, and it changes the elevation, so it belongs in the design conversation early rather than in the survey.
What U-value do replacement doors have to meet in England?
Approved Document L, Volume 1: Dwellings (2021 edition incorporating the 2023 amendments) sets the limit in Table 4.2. A replacement window must reach 1.4 W/(m²·K) or Window Energy Rating Band B. A door with more than 60% of its internal face glazed must reach 1.4 W/(m²·K) or Doorset Energy Rating Band C; other doors, 1.4 or Band B.
Table 4.2 gives two routes to the same outcome, and that is deliberate. A doorset can satisfy Part L on the energy-rating route while its headline U-value sits above 1.4 — which is why a published system figure is a starting point, not a compliance certificate. Paragraph 4.8 adds a second test that catches people out on period properties: the replacement must also be no worse than the element being replaced.
There is a heritage route as well. Paragraph 4.10 provides that where windows or fully glazed external doors cannot meet Table 4.2 because of the need to maintain the character of the building, they should either not exceed a centre-pane U-value of 1.2 W/(m²·K), or single glazing should be supplemented with low-emissivity secondary glazing. In practice a thermally broken steel look aluminium doorset clears the main table comfortably, so the heritage route rarely needs to be argued.
Do you need planning permission for Crittall style doors?
Usually not on an unlisted house outside a designated area. The Planning Portal’s position is that permission is typically not needed for “insertion of new windows and doors that are of a similar appearance to those used in the construction of the house”. Three situations change that answer, and all three should be checked before an order, not after.
- Listed buildings. “If you live in a listed building, you will need listed building consent for any significant works — internal or external.” That includes internal screens, which people routinely assume fall outside consent because they cannot be seen from the street.
- Designated areas. In a conservation area, national park or area of outstanding natural beauty, “there may be additional restrictions in place”. Restrictions are local, so the test is what your authority’s own guidance says about that area, not what the national position allows.
- Article 4 directions. A council can withdraw permitted development rights by direction, at which point works that would otherwise be automatic need an application. These are area-specific and easy to miss.
Part L runs a parallel exemption. Paragraphs 0.8 and 0.9 provide that work to a listed building, a building in a conservation area, or a scheduled monument does not need to comply fully with the energy efficiency requirements where doing so would unacceptably alter the building’s character or appearance — but must comply where it would not. Conservation officers generally take steel look aluminium well, because the profile proportions can be matched to what was there rather than approximated.
None of this is legal advice on your specific property. It is the sequence: establish designation and any Article 4 direction, get the conservation officer’s view on bar width and layout, then specify.
Steel look aluminium or original steel — what actually changes?
Three things: the thermal path, the maintenance obligation, and the size envelope. Aluminium profiles carry a polyamide thermal break that separates inside from outside; steel sections of the original type do not. Aluminium does not rust, so a powder-coated finish is a cleaning job rather than a repainting cycle. And aluminium extrusions reach panel sizes that period steel sections were never asked to span.
Restoring genuine steel windows is a legitimate and sometimes required choice, particularly where a listing turns on the original fabric. Where aluminium is permitted, the trade-off is straightforward: you keep the elevation and you lose the cold frame, the condensation on the section, and the repainting.
Where Crittall style doors work best
Externally, the style earns its keep on rear elevations of interwar and Victorian houses, on garden rooms, and on outbuilding conversions — anywhere a large opening would otherwise read as a single undivided sheet of glass. The grid gives the glazing a scale that relates to the brickwork around it.
For openings wide enough that hinged doors stop being practical, Crittall style bifold doors take the same bar detail across a folding set, with panels to 1200mm wide and 3000mm high and up to seven leaves per side. The house pictured at the top of this page carries the full treatment — doors, screens and fixed lights right across the rear elevation, with the bar grid running unbroken through all of it. The Uxbridge bay pictured above is the opposite end of the scale: one opening, French doors in Textured Black, the bar layout drawn to match the opening rather than ordered from a menu.
Internally, steel look internal doors and screens are doing most of the work in the style at the moment — dividing a through-room without losing light, closing off a kitchen from a snug, or fronting a home office. Internally there is no thermal or weather duty, so the specification is purely about proportion, glass and hardware.
Where we install Crittall style doors and windows
Direct Trade Windows has supplied and installed over 260 projects on its Heritage steel look platforms. The densest patches, by postcode:
Streatham Hill and Streatham (SW2, SW16)
Our single busiest steel look territory — 11 Heritage-system projects across the two districts. A lot of this stock is genuinely Crittall-era: 1930s housing that was built with steel windows, so a steel look replacement here is a restoration of what the street already looks like, not a fashion choice.
Notting Hill, Shepherd’s Bush and Battersea (W11, W12, SW11)
Eleven projects across these three districts, almost all of it Victorian terrace work — rear extensions, side returns and garden-level openings where the bar grid stops a wide span of glass reading as a hole in the elevation.
Windsor, Maidenhead and Slough (SL4, SL6, SL1)
Eleven projects on the factory’s own doorstep. Everything is fabricated in Slough, so for these postcodes the survey, fabrication and installation chain is minutes long — useful when a conservation officer near the Castle wants a sample section to look at.
Berkhamsted and the Chilterns (HP4, HP1, HP22)
Nine projects across Berkhamsted, Hemel Hempstead and the Aylesbury villages — market-town conservation areas where bar width and layout get discussed before anything is ordered.
The Surrey estates (KT11, KT12, TW20)
Cobham, Walton-on-Thames and Englefield Green, including work on private estates — where our teams work to estate hours-of-restriction, gate and vehicle-access protocols, and security requirements as standard practice.
Hove (BN3)
Four projects on Regency and Victorian seafront stock, where the slim dark frame sits naturally against painted render and canted bays.
The Uxbridge bay photographed through this article is one of these projects; every image on this page is our own work.
Buy from the fabricator, not a reseller
Direct Trade Windows fabricates its aluminium in Slough and installs nationwide. On steel look work that matters for two reasons. Bar layouts get set on the drawing rather than ordered from a fixed menu, so the grid can be made to line through between a door and its flanking screens. And curved and arched work is bent in-house, down to a 350mm minimum radius with a ±1mm tolerance — which is what makes an arched steel look opening a specification rather than a special.
Finishes run to standard and non-standard RAL, metallic, textured and anodised effects, with dual colour available — Anthracite Grey RAL 7016 and Jet Black RAL 9005 remain the two most requested on this style. Hardware options include art deco lever handles, monkey tail handles and pull bars in heritage bronze, satin black and polished chrome.
Working out bar width, platform or consent?
Send us the elevation and we will spec it properly — fabricated in Slough, installed nationwide.
Sources
- Approved Document L, Volume 1: Dwellings (2021 edition incorporating 2023 amendments), paragraphs 0.8–0.9, 4.8, 4.10 and Table 4.2 — GOV.UK
- Planning Portal, doors and windows — planningportal.co.uk
- Crittall Windows Ltd — trademark notice and company history, crittall-windows.co.uk
- Direct Trade Windows published system data: Crittall style windows, steel look doors
