Six ways that Crittall Windows can enhance your extension

• 7 October 2024
• News

Crittall Corporate W20 steel patio doors spanning the full width of a rear extension. Slim steel frame profiles maximise the glazed area and allow unobstructed views to the garden.

For more than 100 years Crittall has put the wow factor into home improvement projects of all shapes and sizes and today, when the industrial look is the last word in chic, the demand for Crittall products remains as robust as ever.

Why? Because Crittall is a byword for a unique blend of form and function that brings light and elegance to any space, indoors or outdoors. In this blog we’ll look at how you can incorporate our windows into your extension project, transforming your living area and enhancing your property’s aesthetic appeal.

Why Choose Crittall Windows for Your Extension?

With their distinctive slim steel frames, our windows have been a hallmark of quality and style since 1849. Their timeless design complements both traditional homes and contemporary architect-designed properties, making them an ideal choice for extensions. By opting for our glazing, you can create a seamless connection between indoor and outdoor spaces, maximise natural light and achieve a sophisticated industrial look that’s both on-trend and enduring.

Steel is the only frame material that can achieve impressively slim sightlines whilst remaining structurally self-supporting — a quality synonymous with Crittall windows that means a greater proportion of each opening is glass. The result is more daylight reaching the room, cleaner views to the garden, and a visual lightness that no other material quite achieves at scale.

Our W20 TE thermally enhanced range achieves U-values as low as 1.4 W/m²K, making it fully compliant with Approved Document L of the Building Regulations and the natural specification choice for any new extension that must meet today’s energy efficiency standards. The thermal break within the frame prevents cold bridging — the process by which heat escapes through a conductive frame — keeping your extension warmer in winter and more comfortable year-round. Every W20 TE window and door comes with a 10-year standard warranty and is manufactured from 100% recycled steel, making it as responsible a choice as it is a beautiful one.

All Crittall external door systems carry PAS 24 enhanced security certification across the full range — the standard increasingly required for ground-floor extension glazing and specified by architects and structural engineers on new residential builds.

A note on planning permission

Before specifying your glazing, it is worth understanding where your project sits from a planning perspective. Most single-storey rear extensions fall within Permitted Development rights and require no formal planning application. However, if your property is listed or sits within a Conservation Area, Listed Building Consent will be required — something Crittall is exceptionally well placed to assist with. Our steel frames have been approved for use in listed buildings and heritage settings across the UK for generations, and our team can provide the technical drawings and product specifications needed to support a planning submission. If in doubt, always confirm with your local planning authority before work begins.

1. Create a Stunning Glass Box Extension

One of the most striking ways to use Crittall windows in your extension is to design a glass box-style addition to your home, using our frames to create entire walls of glazing, allowing for panoramic views and flooding your new living space with daylight. A glass box extension can serve as a beautiful kitchen, dining area, or relaxing lounge, offering a modern look that blends seamlessly with your entire floor garden or terrace.

The glass box style works particularly well on Victorian and Edwardian terraced properties, where a rear extension can feel hemmed in on either side. By using full-height Crittall glazing across the back elevation — often combined with a flat or glazed roof — the result is a room that feels open to the sky and garden regardless of the plot’s dimensions. The slim steel grid of the frames adds architectural rigour to what might otherwise feel like a simple conservatory, giving the space a considered, designed quality that reads immediately from both inside and out.

For the best result, work with your architect to position the glazed walls to make the most of your garden aspect. South and west-facing elevations benefit most from full-height glazing, whilst east-facing extensions may suit a more considered combination of glazed panels and solid wall to manage morning light and privacy. For the extension glazing itself, specify the W20 TE thermally enhanced system to ensure the glazed walls meet Approved Document L without the need for additional insulation measures.

2. Install Crittall Patio Doors for total Indoor-Outdoor Living

Replace traditional French doors or bifolding options with our elegant patio doors to create a stylish transition between your interior and exterior spaces. These doors can span the entire width of your extension, opening your living area to the garden and bringing the outside in. The slim profiles of our frames ensure that you’ll enjoy unobstructed views and plenty of natural light all year round.

The practical difference between Crittall sliding patio doors and bifolding alternatives is significant once the extension is lived in. Bifold doors fold inward, requiring a clear floor zone when open — space that frequently conflicts with kitchen islands, dining tables, or seating arrangements. Crittall sliding doors glide parallel to the wall, requiring no clearance zone, and when closed the continuous steel sightlines read as a glazed wall rather than a door system.

Our patio doors are available in a range of configurations — from two-panel sliding options to wider multi-panel arrangements that can open an entire rear elevation. All external door systems carry PAS 24 security certification, and the W20 TE door range achieves U-values as low as 1.4 W/m²K, meeting Approved Document L and ensuring your extension performs as well in winter as it looks in summer.

For homeowners replacing existing French or bifolding doors in a completed extension, a Crittall replacement typically requires minimal structural alteration. The existing structural opening can generally accommodate our frames directly, and our team can advise on the most practical configuration for your opening size at the enquiry stage.

3. Incorporate a Room Divider

For open-plan living spaces, consider using a bespoke internal screen as a room divider. This allows you to maintain an airy, open feel while creating distinct zones within your extension. A room divider can separate your kitchen from the dining area or living room, providing a sense of definition without compromising on light or space.

Unlike a solid partition wall, a steel-framed internal screen allows borrowed light to travel freely between rooms — a quality that matters enormously in extensions where one side of the space receives significantly more natural light than the other. A glazed screen positioned between a rear kitchen extension and a darker hallway or dining room can transform the feel of both spaces simultaneously.

Our Innervision range of internal screens is designed specifically for this application, offering a wide variety of panel configurations, opening options, and finishes. Screens can be fixed, hinged, or sliding depending on how you intend to use the space, and every frame is made to measure to suit your opening precisely. Glass options include clear, textured, and privacy glass, giving you precise control over how much light passes between spaces and how much visual separation you wish to maintain. The result is a feature that feels integral to the architecture rather than a retrofit.

4. Add Character with Internal Doors

Extend the industrial aesthetic throughout your home by installing slimline steel internal doors between your extension and existing living spaces. These sleek, steel-framed doors (which can be made in a wide range of colour options including any BS colour or custom shade, as well as our iconic black) create a cohesive look and allow light to flow freely between rooms. They’re particularly effective in side extensions or when connecting a new kitchen to the rest of the ground floor.

One of the most consistent observations from architects working on extension projects is that the junction between old and new is where the design either succeeds or fails. A Crittall internal door at this threshold — repeating the steel frame language of the extension glazing — draws the two parts of the house into a single, coherent scheme. The frame becomes a design motif rather than a functional separator, and the extension feels like an intentional addition rather than a room that was built onto the back.

The factory-applied powder coat finish on all Crittall internal doors produces a surface that is far more durable than site-painted timber or aluminium. It does not chip in the way that conventional paint does, does not require periodic repainting, and holds its colour consistently over time — a practical consideration that is easy to overlook at the specification stage but appreciated considerably once the house is lived in.

Internal doors with glazed panels are also available with a variety of glass options, from clear to textured and privacy glass, giving you precise control over how much light passes between spaces and how much visual separation you wish to maintain.

Crittall Innervision internal doors with full-height sidelights. Every frame is made to measure and finished in any BS or RAL colour. The factory-applied powder coat does not require periodic repainting.

5. Create a Stunning Orangery-Style Extension

Combine the elegance of a traditional orangery with the modern appeal of Crittall’s windows to create a unique extension. Use our frames to form large windows and doors around the perimeter of your new space, topped with a glass roof or lantern. This approach works beautifully for dining areas or relaxing lounges, offering a light-filled retreat that can be used for many purposes.

The orangery format suits Crittall glazing particularly well because the steel frame carries a material seriousness that aluminium alternatives tend to lack. Where an aluminium-framed orangery can feel lightweight or impermanent, a Crittall-framed version has structural presence — the frames are part of the architecture, not just a cladding system placed over it.

Combining a Crittall perimeter with a structural brick or stone upstand — the traditional orangery format — gives the best of both worlds: the thermal mass and solidity of masonry at low level, and the openness and light of full-height glazing above. This combination is also well received by planning authorities in sensitive areas, as the masonry element grounds the structure and reduces its visual impact from the garden.

For year-round use, specify the W20 TE thermally enhanced system throughout the perimeter glazing and ensure the glazed roof element is independently assessed for thermal performance to Approved Document L standards. A well-specified Crittall orangery is a usable room in every month of the year, not simply a summer addition.

6. Embrace Industrial Chic with Exposed Brick and Crittall Glazing

For a bold, urban-inspired look, pair our bespoke windows and doors with exposed brick walls in your extension. This combination of raw materials and sleek glazing creates a striking contrast perfect for modern kitchens or living spaces. The black steel frames of our windows complement the texture of exposed brick, resulting in a sophisticated industrial aesthetic that is sure to impress.

The pairing of black steel and exposed brick has become one of the most enduring combinations in contemporary residential architecture — and for good reason. Both materials are honest in nature: brick is structural, steel is structural, and neither requires any decorative covering to justify its presence. The result is an interior that feels considered rather than decorated, where every element is doing genuine work.

For this look to succeed, the details matter. Specify our frames in our iconic black or a similarly deep tone to complement the warmth of the brick, and avoid over-finishing the surrounding surfaces. Polished concrete floors, rough plaster walls, and exposed timber ceiling joists all work in sympathy with the aesthetic — the Crittall frames become the architectural spine around which the rest of the interior is organised.

Our bespoke manufacturing capability means that frames can be produced to any size, shape, or configuration your project requires — including non-standard angles, arched heads, and asymmetric layouts that would be difficult or impossible to achieve accurately in aluminium or uPVC. All frames are manufactured at our factory in Witham, Essex, and our technical team can work directly from your architect’s drawings to ensure the finished frames align precisely with the intended design.

Working with Crittall on your extension project

Every Crittall project begins with a conversation. Whether you are at the early concept stage working alongside an architect, or already in possession of planning approval and building regulations drawings, our team can advise on the most appropriate product range for your extension type, confirm the thermal performance of the specification, and provide the technical drawings needed for a building regulations submission.

All Crittall products are manufactured at our factory in Witham, Essex — the same facility where Crittall frames have been produced since 1849. We have complete control over the entire manufacturing process, which means every frame is individually made to order in the UK. Lead times, configurations, and finish options are best discussed at the earliest possible stage of your project.

If you’re planning an extension that is stylish, beautiful and practical, Crittall offers versatile solutions, whether you’re creating a glass box addition, installing elegant patio doors or incorporating internal screens. For more information contact us here or call 01376 530 800.