Grade I & II Listed Building Window Replacement: How To Upgrade Without Losing Character

• January 8, 2026
• General

Owning a listed property is a privilege that comes with unique responsibilities. Whether you’re caring for a Grade I building of exceptional interest or a Grade II structure of special interest, replacing windows requires careful consideration and a deep understanding of heritage requirements.

The good news? You don’t have to choose between preserving historical character and improving thermal efficiency. With the right approach and authentic Crittall steel windows, it’s entirely possible to upgrade your listed property whilst respecting its heritage value.

Understanding listed building requirements

Before considering any window replacement, it’s crucial to understand your property’s listing status and what it means for alterations.

What does your listing grade mean?

Grade I buildings represent structures of exceptional interest, accounting for just 2.5% of all listed properties. These buildings require the most stringent protection and any alterations need exceptional justification.

Grade II properties make up around 92% of listed building windows and are recognised for their special interest. Whilst still requiring listed building consent for alterations, there may be slightly more flexibility depending on individual circumstances.

Getting consent from local planning authority

Any work affecting the character of a listed building requires listed building consent from your local planning authority. This applies even if your property sits within a conservation area where standard planning permission might otherwise be more straightforward.

Like-for-like replacement principles

When grade I and II listed building window replacement is necessary, matching the original design in terms of materials, proportions, and detailing is paramount. This means:

• Replicating the profile and sight lines of original style windows
• Using appropriate materials that match the original fabric
• Maintaining authentic glazing patterns and bar widths
• Preserving the historic character through accurate detailing

Why Crittall steel windows are perfect for listed properties

For many historic buildings, particularly those from the early 20th century or properties with an industrial heritage, Crittall steel windows represent an authentic and historically appropriate solution for grade i and ii listed building window replacement.

A heritage dating back to 1884

Crittall’s heritage stretches back to 1884, with their distinctive slim steel profiles becoming synonymous with the Art Deco era and early modernist architecture. For buildings of this period, Crittall windows aren’t just sympathetic – they’re historically accurate.

Listed properties built between the 1920s and 1960s often featured original Crittall windows. Today, replacing deteriorated steel windows with authentic Crittall products maintains historical integrity whilst meeting modern performance standards.

Authenticity that conservation officers recognise

Specifying Crittall windows for listed property applications, you’re choosing products with proven historical precedent.

The inherent strength of steel allows for remarkably slim frames and maximum glazing area, replicating the appearance of original designs whilst incorporating modern performance features. This makes Crittall windows ideal for:

• Properties originally fitted with steel windows
• Buildings from the Art Deco and modernist periods
• Industrial conversions with heritage value
• Listed properties requiring authentic character preservation

Lightfoot Windows: your Crittall specialist partner

At Lightfoot Windows, we’re proud to be the largest and most experienced Crittall specialist within the Crittall network. Since 1935, we’ve been at the forefront of authentic steel window supply and installation, making us uniquely qualified to guide listed building owners through the complexities of heritage window replacement.

Our Crittall window range for listed buildings

We offer an extensive range of authentic Crittall steel windows and doors specifically suited to heritage properties:

Crittall Homelight Range – The most popular choice for residential listed properties, offering authentic slim profiles with modern thermal performance. Available in various configurations including casement windows and French doors. The Homelight range achieves WER (Window Energy Rating) B & DSER (Doorset Energy Rating) up to A+.

Crittall W20 Range – The W20 range maintains characteristic Crittall aesthetics whilst dramatically reducing heat loss compared to original single-glazed windows.

Crittall W20 TE Range – Our thermally efficient option, ideal for conservation areas where improved thermal performance is required without compromising authentic appearance. This range achieves a thermal gradient equivalent to a thermally broken steel section whilst maintaining traditional appearance.

Bespoke Heritage Windows – For properties requiring exact replication of original designs, we create custom Crittall windows manufactured to precise specifications, ensuring perfect integration with your listed building’s existing character.

Can I install double glazing in a listed building?Yes, but care must be taken to ensure the double glazing does not negatively impact the building’s character. Slim double glazing within authentic steel frames (like Crittall) often gains approval for use in listed buildings as it maintains slim profiles whilst improving performance.

Meeting modern standards whilst respecting history

One of the biggest concerns for listed property owners is balancing heritage requirements with practical improvements in thermal efficiency and energy efficiency. Our Crittall products address these concerns directly.

Double glazing in authentic steel frames

Modern Crittall windows can incorporate double glazing within their slim profiles, offering substantial improvements in heat loss reduction compared to original single-glazed windows. This means:

• Warmer rooms and reduced energy costs
• Condensation reduction
• Improved acoustic performance
• Enhanced security with modern locking systems

All whilst maintaining the authentic appearance that conservation officers require.

Superior thermal performance

The Crittall W20 TE ranges feature thermal technology that dramatically improves thermal efficiency. For listed buildings where building regulations still apply, these thermally profiles achieve the thermal gradient equivalent of a thermally broken steel section.

Durable, low-maintenance protection

Our Crittall windows feature powder coat finishes that provide long-lasting protection against the elements. This durability is particularly valuable for listed properties where frequent maintenance can be disruptive and costly.

Available in various RAL colours, including the iconic black steel finish, you can match existing heritage windows or complement your building’s original materials and colour scheme.

Visit our London showroom

Experience the beauty of authentic Crittall windows firsthand at our London showroom. Here you can explore the our Crittall range in person, helping you visualise how they’ll look in your listed property.

Appointments allow our specialists to discuss your specific project, answer questions about the consent process, and provide guidance on the best option for your building’s particular requirements.

Ready to discuss your listed property project? Contact Lightfoot Windows today

Get in touch with our specialist team to explore how authentic Crittall windows can transform your heritage building:

Fill out our online contact form for detailed enquiries about your listed building project, call 020 8662 9090 to speak with our team or email general@lightfootwindows.co.uk.

Want to get a quick estimate on new Crittall windows? Simply visit our ‘Get An Estimate’ page and fill out the required information and one of our experts will get back to you within 48 hours.