Complete Guide to Secondary Glazing

At Fox Windows & Doors, we’ve installed hundreds of secondary glazing systems across the Midlands, and we’ve seen the difference they make firsthand: quieter homes, better insulation, and preserved period features.

This guide brings together our expertise to help you decide if secondary glazing is right for your home. Inside, you’ll find:

 ✔ How secondary glazing works and where it’s most effective
✔ The key differences between secondary and double glazing
✔ Answers to common homeowner questions
✔ Important considerations for listed and conservation properties

As a trusted installer of bespoke secondary glazing from Granada, we work with the UK’s leading manufacturer to provide high-performance solutions. Their slim, durable aluminium frames are custom-made to fit discreetly behind your existing windows, enhancing insulation and improving acoustic performance without altering the character of your home.

Whether you’re looking to eliminate draughts in a Victorian terrace, maintain the charm of a listed cottage, or reduce street noise in a modern apartment, this guide will help you take the first step toward a warmer, quieter home.

Secondary glazing is an internal window added to the inside of your existing windows to improve insulation, reduce noise, and boost security – without changing how your home looks from the outside.

It works by fitting a slim, made-to-measure frame, typically in aluminium or timber, with a single pane of glass (or in some cases, double glazing). This sits just behind your original window, creating a sealed gap of air between the two.

That air gap acts as a layer of insulation, helping to keep heat in, block out sound, and eliminate draughts. 

Unlike replacing your windows, secondary glazing leaves the original window untouched. It’s installed on the inside of the frame, making it a great option for homes where preserving the appearance and character of the windows is important.

We’ve found secondary glazing to be especially beneficial in:

-Period properties and listed buildings – Ideal for preserving original features while improving insulation.

-Homes near busy roads, train lines, or flight paths  – Provides essential soundproofing for a quieter living space.

-Apartments and upper floors – Avoids the need for scaffolding or major disruption when replacing windows.

-Draughty or energy-inefficient homes – Reduces heat loss without the expense of a full renovation.

Windows are one of the biggest sources of heat loss in a home, especially older, single-glazed ones. Even with thick curtains or draught excluders, warmth often escapes through gaps or thin glass, leaving rooms cold and hard to heat.

This is particularly common in period properties, where timber frames may have warped over time, joints have loosened, or small gaps have developed. While ventilation is important, too much air movement around windows can make a home feel draughty and uncomfortable – and lead to rising energy bills.

Secondary glazing is a simple, unobtrusive way to tackle this. By adding an internal layer of glazing behind your existing windows, it creates a sealed air gap that acts as an insulating barrier – helping your home retain heat more effectively.

Key benefits for thermal performance:

✅ Up to 65% less heat loss, making rooms feel warmer, quicker

✅  Fewer cold draughts, especially around older or ill-fitting window frames

✅  Lower energy bills, as less heat escapes through inefficient windows

✅  More stable room temperatures, even in spaces that are typically hard to heat

When fitted well, secondary glazing can bring older or heritage windows much closer to modern energy performance.

It’s also fully reversible, making it a popular, low-disruption option for listed buildings and conservation areas.

From quieter bedrooms to warmer living rooms and lower energy bills, our customers often tell us just how much difference secondary glazing has made to their day-to-day comfort. Whether it’s been fitted in an apartment, a period terrace, or a countryside cottage, the results are often felt straight away.

Here are some of the most common benefits people notice:

1. A quieter home

If you’re near a main road, railway, or busy public space, unwanted noise can be a constant frustration. Secondary glazing provides a real sense of calm, with many customers noticing a big difference immediately – especially in bedrooms and workspaces.

With the right setup, it can reduce noise by up to 80%, helping to create a more peaceful environment inside your home.

2. Warmer rooms, lower energy bills

We regularly hear from homeowners who were struggling with cold spots and rising heating costs. By improving insulation, secondary glazing helps rooms stay warmer for longer – and reduces heat loss by up to 65%.

Some systems can even achieve U-values as low as 0.5 W/m²K, depending on the glass and configuration. That means better thermal performance without replacing your existing windows.

3. A discreet boost to security

For properties with vulnerable windows, like ground floors or accessible upper levels, secondary glazing can also offer added reassurance. Options such as laminated glass and lockable catches help improve security without changing the look of your home.

4. Designed to suit your space

Customers often ask whether secondary glazing will look out of place, especially in period or character homes. In fact, the frames are slim, subtle, and made to blend in with your existing windows.

With a choice of up to 200 colours, you can match the frames to your existing decor — whether that’s a classic white, a warm heritage tone, or something bolder like anthracite or black.

This is a question we’re asked all the time. Both options improve comfort, energy efficiency, and noise levels but they work in different ways and suit different situations.

Here’s a simple comparison to help you understand the key differences:

In short? If your current windows are in poor condition and you’re happy to change the look, double glazing may be a good fit. But if you want to retain the style and character of your windows, especially in period or listed homes, secondary glazing is often the better choice.

For many of our customers living in listed buildings or conservation areas, secondary glazing is one of the only ways to improve comfort without compromising the look and feel of their home.

We’ve worked on a wide range of heritage properties across the Midlands, helping homeowners reduce draughts, cut heat loss, and enjoy quieter spaces — all while keeping their original windows in place. Because secondary glazing is fitted on the inside, there’s no alteration to the external appearance and no damage to the existing frames or glass.

It’s widely recognised by heritage organisations, including Historic England and the National Trust, as a sympathetic and reversible way to improve the performance of protected buildings.

Why do heritage homeowners choose secondary glazing?

✅ No changes to your original windows

Secondary glazing works with your existing timber, sash, or metal frames.

✅ Low visual impact

Slim aluminium frames are designed to be discreet and sit inside the property, barely visible from the outside.

✅ Improved thermal and acoustic performance

Many listed buildings are cold and noisy — secondary glazing can reduce heat loss by up to 65% and external noise by up to 80%.

✅ Fully reversible installation

If regulations change, or you choose to remove it in the future, the system can be taken out with no damage to the original windows.

If your home is listed, you’ll likely need Listed Building Consent before making any changes, including internal ones like secondary glazing. Every local authority is different, so it’s important to speak to your local planning team or Conservation Officer early on.

While secondary glazing is often supported as a reversible and low-impact upgrade, some councils may have specific requirements for things like frame colour, positioning, or the type of glass used.

We’re happy to share what we’ve learned from other heritage projects and guide you through what’s typically required.

👉 You can also refer to Historic England’s guidance on secondary glazing for additional detail on what’s usually acceptable in listed and historic properties.

What types of secondary glazing are available?

Once you’ve decided secondary glazing is the right solution for your home, the next step is to choose the right configuration for your windows. Different styles suit different window types, whether you have sash windows, casement windows, large bays, or smaller panes.

At Fox Windows & Doors, we install a full range of Granada secondary glazing systems. All are made to measure and designed to be discreet, secure, and easy to use.

To help you explore your options, here’s a quick overview of the most commonly used configurations — along with short videos so you can see how they work in real homes:

Hinged Units

Best for easy access to the original window (e.g. for cleaning or opening)

HU-SL (Slimline Hinged Unit)

HU-SL DH (Heavy Duty Slimline Hinged Unit)

Horizontal Sliding Units

Ideal for wide window openings or where access is needed to individual panels

HS2 – 2 Panels

HS3 – 3 Panels

HS4 – 4 Panels

HS5 – 5 Panels

Vertical Sliding Units

Perfect for sash windows and traditional vertical-opening frames

BVS (Balanced Vertical Slider)

TBVS (Tilt-In Balanced Vertical Slider)

Not sure which type would suit your windows best?

We’re always happy to recommend the right configuration during your design consultation, based on what works best for your home, how often you open the window, and how much access or ventilation you need.

Case Studies

We know it helps to see real examples, especially if you’re wondering how secondary glazing will look in your home or how much of a difference it will actually make.

Below are two case studies from Granada, the UK manufacturer whose systems we install. They showcase the kind of results secondary glazing can achieve in both heritage and high-noise settings. While these aren’t Fox Windows & Doors installations, they’re great demonstrations of what’s possible.

🎥 Noise insulation near the M62

This video shows how secondary glazing helped a homeowner dramatically reduce traffic noise near one of the UK’s busiest roads.

Watch Now 

Granada case study

🎥 Murray’s Mill, Manchester

A Grade II listed building converted into apartments. Secondary glazing was used throughout to preserve the character of the windows while improving insulation and acoustic performance.

Watch Now 

💬 What our customers say

“There are a lot of companies out there offering double and secondary glazing and it’s a bit of a minefield choosing the right one. I must admit we spent quite some time looking at reviews and that led us to Fox windows and Doors. This is one of the main reasons I wanted to leave a review after our project, so other people could gain from our experience. From the beginning the customer service was great, always someone available to deal with questions and issues. ….. We are really pleased with the final result and would recommend Fox windows and Doors to anyone in need of similar work. read less

Christine in Warwickshire Posted on 31/10/2022 , work completed 28/10/2022

At Fox Windows & Doors, we take pride in working closely with our customers to find the right solution for each home. Whether you’re upgrading a single window or planning a whole-house installation, we offer:

A free design consultation  to talk through your needs, preferences, and any listed building considerations

A complimentary technical survey to ensure every measurement is spot-on and the installation goes smoothly

Advice on meeting Building Regulations and achieving the best performance for your property

Because every project is bespoke, costs vary depending on the number of windows, the type of glazing, and the chosen configuration. However, secondary glazing is often a more affordable option than full window replacement, particularly when your existing windows are in good condition.

We offer:

✅ Transparent pricing

✅ No-obligation quotes

✅ Tailored solutions to suit your budget, property type, and goals

We install secondary glazing across Warwickshire, Leicestershire, the West Midlands, and surrounding areas – including Kenilworth, Leamington Spa, Redditch, Rugby, Solihull, and Stratford Upon Avon.

Get in touch today for friendly advice or a free quote.