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TRADING SINCE 1849

Crafting beautiful steel windows and doors since the reign of Queen Victoria.

HANDCRAFTED TECHNOLOGY

High-quality, hand-crafted products that are designed to last a lifetime.

NATIONWIDE COVERAGE

Discover our exceptional products no matter where you are in the UK.

Orangery with external Crittall doors

Key Steel Windows Features For Extensions:

Our steel windows offer a host of benefits for extensions, these include:

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Maximises Natural Light 

The ultra-slim frames of our steel windows allow generous glazed areas, flooding your extension with natural light and connecting interiors to the garden.

SLIM, MINIMAL SIGHTLINES

Narrow profiles create a clean, contemporary look that suits both period homes and modern builds, giving your extension a refined, architectural finish.

THERMAL COMFORT ALL YEAR ROUND

Designed to work with high-performance double or triple glazing, our steel windows help keep extensions warm in winter and cool in summer while reducing energy use.

Additional Features

Design Flexibility

Our Steel Windows for Extensions offer impressive design flexibility with a variety of configurations and customisation options, allowing you to customise the look and functionality of your business.

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Popular Colours

Black
Traffic Grey
Agate Grey
Light Grey
White
Pastel Green

A colour to suit your project

Our Steel Windows for Extensions are available in a range of colour options including our iconic black steel. You can also choose from any RAL colour, enabling you to find the perfect fit for your project or business. Get in touch with your local Crittall approved installer for more information.

Selected: Black

Black

Selected: Traffic Grey

Traffic Grey

Selected: Agate Grey

Agate Grey

Selected: Light Grey

Light Grey

Selected: White

White

Selected: Pastel Green

Pastel Green

Hardware

Hardware

Discover the perfect finishing touches for your Crittall window with our exquisite hardware options, featuring both the timeless Classic Collection and the opulent Luxury Collection to suit every style and preference.

Soho Casement Handle

Soho Casement Handle

Phoenix Casement Handle

Phoenix Casement Handle

Deco Casement Handle

Deco Casement Handle

Berkeley Casement Handle

Berkeley Casement Handle

Arched Casement Handle

Arched Casement Handle

Straight Casement Handle

Straight Casement Handle

Scroll Casement Handle

Scroll Casement Handle

Curved Casement Handle

Curved Casement Handle

Curved Peg Stay

Curved Peg Stay

Straight Peg Stay

Straight Peg Stay

Sliding Stay With Round Knob

Sliding Stay With Round Knob

Sliding Stay With Butterfly

Sliding Stay With Butterfly

Single Folding Opener

Single Folding Opener

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  • Case Studies

Our Recent Work

Modern property exterior featuring black crittall windows and doors with glass balustrade balcony

Restoration in rural Sussex by Lightfoot Windows

This project, executed by our specialist reseller Lightfoot Windows, focused on a listed property in...

Modern property with white facade, featuring crittall steel windows and doors

Modern renovation in South Yorkshire by KJA Services

The Crittall House of the Year (CHOTY) awards celebrate our commitment to excellence by recognising...

Exterior of Adelaide House, an office building in London

Crittall windows that truly stand the test of time

Crittall Windows recently returned to Adelaide House in London to replace the steel windows it...

Black steel french internal doors

Crittall House of the Year Award Winner 2023

Congratulations to the deserving winners of this year's Crittall House of the Year Award with...

Full installation of light grey steel bespoke windows, casement windows, and french doors

Crittall House of the Year Award – Runner Up 2023

When the owners were planning the renovation of their house, they knew they wanted to...

Crittall Window Display

Crittall’s Window Display

A town centre shopping mall in Stroud, Gloucestershire, has been given a new lease of...

Compare Crittall® Window Styles

Find the right window for your project.

Why Choose Steel Windows for Extension Projects

Steel windows define the character of an extension. Their thin frames – a hallmark of Crittall’s designs – maximise natural light while maintaining strength. Large glazed areas brighten living, dining and kitchen spaces so extensions feel open and garden-focused.

The visual impact is matched by practicality. Manufactured from hot-dip galvanised steel, Crittall windows are durable, corrosion-resistant and low maintenance. Their clean lines suit period homes and new builds, while multiple configurations and colours let you tailor each elevation, door set or internal screen.

For extensions, steel offers impressive versatility. Whether you are planning a glass-box addition, kitchen-diner knock-through or internal room divider, Crittall delivers the crisp geometry and slim mullions architects favour. Frames accept double or triple glazing to meet insulation standards, reduce noise and enhance security.

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Internal french doors with sidelights
Crittall Windows Corporate W20 external doors

Crittall Steel Window Systems for Residential Extensions

Corporate W20 Windows feature traditional, slender steel framing with welded corners and industrial detailing. Accepting double-glazing up to 16.4mm and finished with polyester powder coating, W20 suits heritage properties and renovations where original character must be preserved.

Corporate W20 TE (Thermal Efficient) brings higher energy performance to the same profile. Achieving U-values around 1.4 W/m²K, W20 TE helps extensions meet Approved Document L while maintaining slim sightlines. It also accommodates triple-glazing up to 37mm for improved insulation and noise reduction.

T60 Thermally Broken Steel Windows are Crittall’s most advanced system. Integral thermal breaks and fibreglass reinforcement enable whole-window U-values as low as 0.8 W/m²K, ideal for highly glazed extensions. T60 accepts insulating glass units up to 36mm and, with laminated acoustic glazing, can deliver sound reduction around 40dB.

Crittall Homelight® Windows reinterpret classic steel sightlines with contemporary performance. Slim profiles, weather-seals and secure hardware make Homelight a strong choice for residential extensions.

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Extension Applications: Design Possibilities

Steel windows suit modest rear additions and dramatic glass boxes alike. In kitchen or living spaces, floor-to-ceiling glazing and slim mullions create uninterrupted views and a seamless connection to patios or gardens. For glass-box extensions, steel’s strength allows walls of glass that appear almost frameless while remaining weather-tight and secure.

Internally, steel-framed screens and doors act as stylish partitions that control noise and cooking smells yet keep light flowing through open-plan layouts. Fully glazed corners, clerestory bands or feature gables can all be realised using Crittall systems.

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Steel bespoke windows
Crittall steel-framed window with a scenic outdoor view, framed by sleek, modern design.

Building Regulations and Thermal Performance

Modern extensions must comply with thermal standards. Crittall’s W20 TE and T60 systems meet or exceed Approved Document L, while the right glazing further improves U-values and acoustic insulation. All systems are hot-dip galvanised and include gaskets and weather-seals for long-term protection.

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The Crittall Difference

Crittall couples over a century of steel window expertise with rigorous manufacturing. Frames are engineered to precise tolerances, finished with Duralife polyester powder coating and fitted with secure hardware and locks. With minimal upkeep, Crittall steel windows retain their appearance for decades, making them a sound investment for extensions that demand both design impact and lasting performance.

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Black steel windows

Your Crittall® Buying Journey

Our buying guide walks you through the effortless steps to incorporating timeless Crittall products into your project, from initial inquiry to receiving your custom-made steel windows and doors.

Step 1

Enquire with Us

Start your Crittall journey by contacting us. Simply fill out our contact form and expect a response within 24 hours.

Step 2

Understanding Your Requirements

Our team will discuss your project to understand your needs and recommend the perfect Crittall supplier based on your location and requirements.

Step 3

Get Your Quote

We'll connect you with your local Crittall approved installer who will provide a personalised quote for your Crittall project.

Step 4

Purchase

Once you've reviewed your quote and confirmed your order, your custom-made Crittall windows and doors will be crafted especially for you.

Frequently Asked Questions

We understand you may have queries about our products and services. We’ve answered some of the most common questions below.

Are Crittall's steel extension windows energy efficient?

Yes, our steel windows are incredibly energy efficient. They utilise high quality double glazing which effectively works to conserve energy in any property and save money on energy bills.

Are Crittall's steel windows high maintenance?

Not at all. Regularly cleaning with a mild detergent and water will keep them looking their best. Their galvanized coating offers resistance to weathering, rust and corrosion.

Are Crittall's steel windows for extensions available in a range of configurations?

Yes. Our steel windows are available in various styles and configuration options, enabling you to find the right fit for your project or business.

Where can I find inspiration for using Crittall's windows in my business?

Browse our Inspiration Gallery! This section showcases stunning projects featuring windows manufactured by Crittall Windows and provides design ideas to spark your vision.

Can’t find the answer you’re looking for?

Speak to an Expert
Trio of french doors for London home

Start your Crittall journey

Transform your home by finding your local Crittall approved installer. Our specialist partners offer a stress-free service from enquiry to after-sales support.






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    Customer Reviews

    Take a look at some of our customer reviews to see how Crittall windows and doors have transformed real-world spaces. Customer reviews offer valuable insights beyond aesthetics, providing details on installation experiences, long-term performance, and the overall impact Crittall's windows and doors had on their projects.

    The Crittall design meant we could retain a traditional feel which would fit with the overall look of the house.

    KAREN WELSTEAD

    Scotland, UK

    All of our visitors comment on our stunning doors and we all love the beautiful shadows in the kitchen created by the frames – its like a cobweb of shadows!

    HANNAH

    SW London, UK

    ‘Nothing shouts 1930’s elegance like original Crittall windows … We feel as though we are on the set of a Poirot shoot when we walk inside’

    HARRY & VIC

    Lake District, UK

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