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EXTENSIONS & RENOVATIONSCrittall-Style Doors and Glazingfor Extensions
Extensions & Renovations7 min read1 April 2026

Crittall-Style Doors and Glazing for Extensions

Steel-framed Crittall-style doors and windows for extensions - costs, genuine vs replica, thermal performance, and design ideas.

The Crittall look - slim black steel frames with large glass panes - has become the defining design feature of UK kitchen extensions. Whether you're building a side return, rear extension, or simply adding character to an open-plan layout, Crittall-style glazing transforms the aesthetic from standard to striking.

But the price range is vast, and the choices are confusing. Here's what you need to know.

The Options: Steel vs Aluminium vs Budget

Genuine Crittall (Hot-Rolled Steel)

Manufactured by Crittall Windows Ltd - the original company, operating since 1884. Their modern Homelight and Corporate ranges use thermally broken steel profiles with the slimmest sight lines available.

  • Sight lines: 20–25mm (the thinnest on the market)
  • Cost: £3,000–£6,000 per door/screen installed
  • U-value: 1.5–1.8 W/m²K (double-glazed, thermally broken)
  • Finish: Hot-dip galvanised + polyester powder coat (any RAL colour, but black is classic)
  • Maintenance: Repaint every 8–12 years
  • Lead time: 8–14 weeks from order

Best for: High-end extensions, listed buildings, period conversions, maximum visual impact.

Premium Aluminium Replicas

High-quality aluminium systems engineered to replicate the Crittall look with slimmer-than-standard profiles.

  • Sight lines: 30–40mm (wider than steel but narrower than standard aluminium)
  • Cost: £1,500–£3,500 per door/screen installed
  • U-value: 1.4–1.6 W/m²K
  • Finish: Polyester powder coat (no repainting needed)
  • Maintenance: Virtually none
  • Lead time: 4–8 weeks

Brands: Mondrian by Aluco, Origin OW-70, AluK BSC94, Schuco Jansen Janisol

Best for: Most extension projects - 80% of the look at 50% of the cost.

Budget Steel-Look Aluminium

Standard aluminium doors with a stepped or welded glazing bar to suggest the Crittall style. Wider profiles but much cheaper.

  • Sight lines: 40–55mm
  • Cost: £800–£2,000 per door installed
  • U-value: 1.2–1.6 W/m²K
  • Finish: Powder coat
  • Lead time: 2–4 weeks

Best for: Budget projects where the look matters but perfection isn't required.

Cost Comparison: External Doors

For a typical rear opening (2.4m wide × 2.1m high):

Configuration Genuine Crittall Premium Aluminium Budget Aluminium
Fixed screen + single door £4,000–£6,000 £2,000–£3,500 £1,000–£2,000
French doors (pair) £5,000–£8,000 £2,500–£4,500 £1,200–£2,500
3-panel bifold £8,000–£15,000 £3,500–£6,000 £2,000–£3,500
Fixed screen (no door) £2,500–£4,000 £1,200–£2,500 £600–£1,500

Compared to standard aluminium bifolds (£3,000–£6,000 for the same opening), Crittall-style doors are a premium - but they're also the single most impactful design choice in a kitchen extension.

Where to Use Crittall-Style Glazing

1. Rear Extension Doors

The most common application - replacing the traditional bifold or sliding door with Crittall-style French doors flanked by fixed glazed panels. This creates a wall of glass with the elegant grid pattern as a design feature.

Typical configuration: Two fixed side panels + central French doors Cost: £3,000–£8,000 depending on specification

2. Side Return Glazing

In a side return extension, Crittall-style glazing can form the roof-to-floor glass wall that floods the narrow space with light. Because the side return wall is often shared with the neighbour, glazing is limited to the roof and the rear - making the roof glazing line a perfect place for a Crittall-style framework.

3. Internal Partitions

Crittall-style internal screens are transformative in open-plan spaces:

  • Kitchen-to-hallway screen - separates cooking smells while maintaining light flow
  • Home office partition - visual separation with borrowed light
  • Utility room screen - hides laundry while keeping the space connected

Internal screens don't need thermal glazing, reducing cost to £1,000–£3,000 per panel (1.2–1.5m wide × 2.4m high).

4. Shower Screens

Crittall-style shower screens and wet room dividers are a popular bathroom upgrade. A framed glass shower screen costs £300–£800 for a steel-look aluminium version.

5. Glass Links

When connecting a new extension to the existing house (especially on listed buildings), a glazed link creates a visual break. Crittall-style framing gives this link architectural presence.

Design Considerations

Grid Pattern

The signature Crittall look is a grid of rectangular panes divided by glazing bars (also called astragal bars). Options:

Pattern Look Cost Impact
No bars (plain glass) Modern minimal Cheapest
Horizontal bars only Contemporary industrial +10–15%
Full grid (horizontal + vertical) Classic Crittall +15–25%
Asymmetric grid Architect-designed +20–30%

For replicas, bars are typically applied to the glass surface (stuck-on or clip-on) rather than being true divided lights. Genuine Crittall uses welded steel bars that are part of the frame structure - more authentic but more expensive.

Colour

Matt black (RAL 9005 or similar) is the classic choice and accounts for 80%+ of Crittall-style installations. Other popular options:

  • Anthracite grey (RAL 7016) - softer than black, matches many modern window frames
  • Dark bronze - warmer tone, suits period properties
  • White - traditional for original Crittall in some period settings
  • Dual colour - black outside, white inside (aluminium replicas only)

Threshold Details

External Crittall-style doors need a weather-resistant threshold. Options:

  • Low threshold (20mm step) - standard, meets Building Regulations Part M for accessibility
  • Flush threshold - level access for accessibility, requires excellent drainage detailing
  • Raised threshold - most weather-resistant but creates a step

Crittall and Thermal Performance

The historic weakness of steel windows - poor insulation - has been solved by thermal breaks. Modern Crittall and replica products insert a polyamide strip between inner and outer steel/aluminium sections, dramatically reducing heat transfer.

Product U-value Building Regs Compliant?
Original Crittall (single-glazed, no break) 5.0+ No
Modern Crittall (double-glazed, thermal break) 1.5–1.8 Yes
Premium aluminium replica (double-glazed) 1.2–1.6 Yes
Standard aluminium door (double-glazed) 1.2–1.4 Yes

All modern products meet Building Regulations Part L requirements. The Energy Saving Trust recommends checking U-values before purchase - lower is better.

Installation

Crittall-style doors and screens are typically installed by the manufacturer's approved installers or specialist glazing contractors. Key points:

  • Structural opening must be prepared by your builder with an appropriate lintel or steel beam
  • Tolerance is critical - steel frames have very little adjustment compared to uPVC. Openings must be square and correctly sized.
  • FENSA registration - external doors and windows must be installed by a FENSA-registered installer (or inspected under Building Regulations)
  • Lead times - genuine Crittall takes 8–14 weeks from order. Plan around your extension build schedule.

Tip: Order doors and screens before construction starts so they arrive when the opening is ready. Delays on glazing are one of the most common causes of extension overruns.

Next Steps

  1. Decide steel vs aluminium - visit a showroom to compare sight lines and feel
  2. Choose your configuration - French doors + fixed panels is the most popular and cost-effective
  3. Get 3 quotes - from Crittall directly, an aluminium replica supplier, and a budget option
  4. Coordinate with your architect - the door specification affects the structural opening design
  5. Order early - 8–14 weeks lead time for genuine Crittall, 4–8 for replicas
  6. Budget within your extension costs - use our free calculator for the overall project
  7. Check our glossary for terms like sight line, thermal break, U-value, and astragal bar

Frequently Asked Questions

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