We love the simple elegance of sash windows. A quintessentially British classic that has meandered through time since the 16th century. In fact, we love them so much that we’ve created a cutting edge solution to protect their posterity while introducing modern standards of soundproofing and thermal insulation. Introducing: our secondary glazing for sash windows with noise reductions of up to 51dB.


Designed to be installed inside your current frames, our secondary glazing for sash windows is a top of the line soundproofing solution. Your original sashes remain untouched, while our hight performing secondary glazing creates a highly effective sound barrier inside your property. Slender, discreet and efficient, they are perfectly suited to homes in conservation areas and Grade II listed buildings.

Retaining the original sash window, we fit a high-performance single-pane casement window directly behind the existing window, which delivers outstanding soundproofing and greater thermal efficiency. The perfect solution for buildings where the original sash windows cannot be changed or removed, a single-pane casement window installed directly behind the existing sash is the most elegant and efficient option for reducing the noise pollution in inner city homes.

Our single-pane design is far superior to secondary sash windows, which do nothing to reduce noise pollution which continues to leak between the two panes of the sash – just as it does in the existing window.



Slide sideways to see before and after.


Secondary sash windows that are currently available on the market only offer glass with a low dB rating (typically just 37dB) whereas our single-pane secondary windows offer far greater levels of noise reduction, as they are available in 43dB double-glazing, 47dB double-glazing or a 51dB triple-glazing.

Our single-pane design, using high-performance 43dB51dB glass, results in excellent soundproofing capabilities, with clients recording a reduction of up to 55dB58dB. The best secondary window on the market, our single-pane design for sash windows is perfect for anyone living in a particularly noisy area (on a main road, flight path or near a train line, for example) or for those who cannot change their original windows due to being a listed building, under the Article 4 direction, or even for those living in a block of flats.

Of course, we’ll also make recommendations based on our sound survey to ensure you’re getting the right product for your property.


We create fully customised glazing depending on how you want the window to function and the space that you have available.


Side-hinged and tilt and turn, all of our secondary glazing for sash windows is installed with high performance seals to stop noise flanking around the frame.


Our easy-open design is made for optimal usability, allowing you to access the existing sash for maintenance, repairs and to improve ventilation.


A sturdy multi-stage locking system allows for micro ventilation without compromising safety and security, as can be the case with an open sash.


Many of our secondary glazing for sash windows are installed in listed buildings and conservation areas. In other words, properties where preservation is paramount. In addition to the secondary glazing, we can craft and install bespoke panelling, architraves, boxing and more, to ensure the seamless integration of our system within the existing design scheme.

The single-pane secondary window is a much more subtle intervention that fits neatly – almost unseen – onto the back of the existing sash window. Much less bulky and noticeable than a secondary sash, the single-pane system does not obstruct or interfere with the design of the original window, which can be enjoyed from both inside and out.

An excellent choice for smaller spaces, our single-pane secondary windows are fitted directly behind the sash window, whereas other models on the market, including secondary sash windows, often require a deep cavity and a gap of around 150 – 250 mm. Our single-pane secondary windows can be fitted inside the reveal, which looks very subtle and takes very little space – making it the perfect solution in a smaller room. Where it is not possible to fit the secondary window within the reveal itself, the secondary window can be neatly and unobtrusively fitted on to the face of the wall.

Our skilled carpenters are able to replicate the original trims, features and panels that frame the existing sash window, meaning that the secondary window perfectly compliments the original sash, blending seamlessly with the look and style of the building.


Our secondary glazing for sash windows is the ultimate solution to noise pollution. Enabling you to keep your authentic sashes, while also benefiting from modern levels of thermal comfort. Our secondary glazing units have a maximum Ug-value of 0.6 W/m²K, meaning that all of our systems are ultra energy efficient.


We want to help you find the right product that suits you, so whether you want to talk to us about our secondary glazing systems for sash windows, we’re here to help.


Trees for Life is a conservation charity dedicated to rewilding the Scottish Highlands. They currently have 44 tree planting sites and have planted nearly two million trees to date.


  1. What is secondary glazing?

    Secondary glazing, often known secondary glazing systems, are discreet window units that are installed on the inside of your existing sash windows. By creating another barrier, they improve the thermal efficiency of a property while reducing noise pollution. There are a wide variety of secondary glazing systems available on the market. At The Soundproof Windows we create bespoke secondary glazing systems for sash and casement windows. These are custom built to tackle our clients’ specific needs.

  2. How much does acoustic glass cost?

    Secondary glazing is a highly effective solution to noise pollution and heat loss. It is especially useful in properties where you cannot change your existing sash windows, for instance in a listed building, a conservation area or if you are living in a flat inside a larger building.

  3. Can secondary glazing be installed in listed buildings?

    Yes. Secondary glazing can be installed in almost all Grade II listed buildings and other buildings in conservation areas. We work with you and your architects to ensure that all standards are met.

  4. How effective is secondary glazing?

    Our secondary glazing for sash windows boast noise reductions of up to 51dB, and are rated A+ and over for thermal efficiency.

  5. Is it necessary to refurbish my sash windows before installing secondary glazing?

    Typically, our secondary glazing can be installed without any need for refurbishing your existing sash windows. It’s designed to seamlessly integrate and provide comprehensive insulation.

  6. What are the costs associated with secondary glazing?

    The cost varies depending on the size, style, and specific requirements of your windows. We offer a range of solutions to suit different budgets. For an accurate, tailored estimate, please use our ‘Request a Quote’ feature.

  7. Can secondary glazing be installed in listed properties?

    Yes, Soundproof Windows systems are designed for reversible and discreet installation, which doesn’t alter the building’s original fabric. This typically exempts them from listed building consent. However, we recommend consulting with your local conservation officer for confirmation.

  8. Does secondary glazing provide draught exclusion?

    Absolutely. Our units are equipped with high-quality dual compression seals, ensuring effective draught exclusion and enhanced thermal efficiency.

  9. What level of noise reduction can I expect from secondary glazing?

    Our secondary glazing systems can significantly reduce external noise, potentially by up to 99%, depending on your specific window configuration. We invite you to contact us to discuss your needs, and we’ll advise on the best options for your situation.

  10. Will I still be able to ventilate my room with secondary glazing installed?

    One of the advantages of our secondary glazing is its flexibility. All windows remain easily accessible, allowing for ventilation, cleaning, and maintenance. This design ensures that the windows can remain in place throughout the year, adapting to different seasonal requirements.

  11. Is investing in secondary glazing a wise decision?

    Secondary glazing is an excellent choice for those seeking the benefits of double glazing — like improved insulation and reduced energy bills — without the higher costs. Statistically, an average home loses about 18% of its heat through windows. By adding an additional insulating layer, secondary glazing can cut this heat loss by up to 60%, making it a cost-effective and efficient solution.

  12. What is the best way to clean secondary glazing on sash windows?

    Cleaning our secondary glazing systems is straightforward. The design allows the secondary windows to open inward, providing easy access to both the interior and exterior of the glazing unit, as well as the primary window. This ensures hassle-free maintenance and cleaning.

  13. Will I experience condensation with secondary glazing?

    Condensation is highly unlikely with Soundproof Windows’ secondary glazing systems. Our use of double and triple glazing technologies effectively prevents condensation build-up, ensuring clear and moisture-free windows.

  14. How do you install secondary glazing?

    Secondary glazing is installed inside the existing sash window. It is installed so that it does not affect or alter the existing glazing. We also craft and install additional design elements such as architraves and trims to ensure authenticity is preserved.



All of our products come with up to a 10 Year Insurance Backed Guarantee provided by the Consumer Protection Association. So you can rest assured that your home is in safe hands.



We have been Trading Standards Approved and are proud to be enrolled on the Buy With Confidence Scheme, ensuring customers just like you have their interests protected.



Consumers can feel confident using a TrustMark registered business, as the government-endorsed scheme ensures high quality service and a range of consumer protection options.



Following awards in 2020, and 2021, The Soundproof Windows was announced as the ‘Best Acoustic Window & Door Installation Company – London’ at the SME News Awards 2022.