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Secondary Glazing is a cost-effective way to improve the temperature of your home and reduce condensation. By adding a discrete extra layer of glazing placed inside your window frame, it helps insulate existing single and double-glazed windows. Cut-to-size secondary glazing is a customisable approach that precisely addresses the unique needs of your home, ensuring a snug and discreet fit within your window frame.
Secondary glazing also reduces sound pollution and enhances the security of your property. As an innovative approach to window insulation, it offers a range of benefits that extend far beyond its initial cost-effectiveness.
It is also easy to install yourself, we cut the acrylic to size and then you just need to add magnetic tape (sold separately) to your window frame and to the plastic sheet and stick it to the window! You can check out our step by step guide below.
For windows larger than 800mm we recommend using a thickness of at least 4mm, and our magnetic tape for larger windows.
Since our secondary glazing is made of clear acrylic, it can easily be cut to size for any window - even if your windows are circular. Acrylic is also easier to fit than glass due to its lightweight qualities. Due to the optical clarity that acrylic provides, there’s no noticeable difference between the visibility or light transmission of your single-glazed windows and the results of secondary glazing.
If you are unable to replace your existing windows with double glazing, secondary glazing is an ideal alternative which is just as beneficial. Acrylic secondary glazing is compatible with period properties and historic homes. It doesn’t detract from the external character and look of the windows of heritage properties but gives all of the insulating benefits without causing condensation.
Acrylic secondary glazing can be removed easily, meaning when the seasons change, the panels can be removed until the winter. Some people choose to keep their secondary glazing on their windows all year round as it also works to keep out dust, dirt and pollen.
When you install secondary glazing into your property, you achieve the same benefits of double glazing such as less condensation and improved heat transfer. Despite this, secondary glazing is more cost-effective and can reduce heat loss via windows by around 65% - which is 10% more than double glazing.
With a large enough gap between the window and the secondary glazing you could see a 4°C improvement in room temperature resulting in a considerable saving on your heating bill. This is exactly what Mark from Lancashire has experienced, he recently sent us the results from his personal experiment on the effectiveness of his secondary glazing which he has fitted to his existing double glazing:
"When considering the cost of secondary glazing I calculated that if it paid for itself within 2-3 years it was worth it. I only have one month's figures to work on but an indicative 4°C saving means it will reach breakeven point in the winter months of the first year." Read Mark's full findings.
Installing secondary glazing is a fantastic option for those who are looking to insulate against noise, such as those in multi-storey buildings, or with buildings against the road. Once it is fitted, secondary glazing has been found to reduce noise by up to 80% without needing to be fit to the exterior of the frame.
Secondary glazing is more difficult to break than single-pane windows - so it gives more protection to your home.
Step 1: Clean the frame ready for application.
Step 2: Measure and cut the steel tape (thinner tape) for the window frame. For a cleaner look in the corners, you can cut the steel tape at a 45-degree angle for a miter join.
Step 3: Apply the steel tape (Side A) to the window frame. Make sure to leave no gaps in the corners so that it is as air-tight as possible.
Step 4: Stick Side B on top of the previous strips.
Step 5: Remove the protective film from one side of the acrylic.
Step 6: Peel off the backing from Side B to expose the adhesive. Align the acrylic piece with the tape, and press it to the side from which you have removed the protective film against the adhesive surface.
Step 7: Take off the second protective film to reveal your clear secondary glazing sheet installed!
Whether you choose our white or black magnetic tape, we recommend putting the thinner steel tape on the frame of your window and the thicker magnetic tape on the acrylic. This is because if you want to take the secondary glazing off in the summertime, you are only left with a thin, more discrete tape that matches your window frame colour. You can also then apply the Perspex again when winter comes back around.
Perspex® Acrylic is 100% recyclable. Waste products can readily be recovered from the original raw material (the monomer) and re-used in a new sheet.
Perspex® has been manufactured in the UK for over 85 years and still takes place on the same site in Lancashire as it did in the 1930s. This short supply distance to our UK customers helps reduce ‘product miles’ from the manufacturing plant to the end user.
Numerous different investments have already been made by Perspex® to lessen the impact on the environment. Annual waste consumption has been reduced by 24 million litres, and almost 800 tonnes of carbon dioxide have been saved every year as part of a hot water recycling project. At Cut My, we work to be more sustainable by using all of our offcuts to heat our manufacturing facility. We are also currently working towards reducing our packaging.
Clear Perspex® acrylic sheets give excellent optical clarity, ranging up to 92% light transmission, higher than most types of glass, making our clear plastic sheets an advantageous option for use in windows.
Clear Perspex® acrylic sheets are incredibly durable. Often, acrylic secondary glazing is used as a safer alternative to glass as it much more resistant to impact.
Clear acrylic sheeting is UV and weather-resistant, as well as being resistant to prolonged exposure to sunlight. In addition, clear acrylic sheets are also resistant to most chemicals and have a low moisture absorption rate, so clear plastic sheets are useful for a host of different environments and are perfect for outdoor applications.
Secondary glazing with clear acrylic is a more affordable option than new glass windows or double glazing, as it is significantly cheaper and can be installed by any DIYer!
All of our secondary glazing plastic options are equally easy to clean, with just warm soapy water and a microfibre cloth needed to ensure a hygienic finish.
Share your Secondary Glazing photos with us to feature on our website. Simply mention @cutmy.uk on Instagram or upload a photo and tag us!
Here are a few tips to help you maintain the quality of your glazing and keep it functioning smoothly:
Store the Glazing Sheet Flat
When storing your secondary glazing acrylic sheet, keep it flat to avoid bowing. If you must store it upright, ensure it’s supported to stay flat and aligned vertically. Wedge it between a wall and furniture or tuck it behind a cabinet.
Addressing Bowed Glazing
If your glazing sheet has developed a slight bow after storage, don’t worry! Leave it in a position that encourages it to bend in the opposite direction. Check periodically to see when it has straightened out.
Avoid High Temperatures and Opposing Magnetic Fields
Magnetic tape can lose effectiveness if exposed to high temperatures or nearby opposing magnetic fields. Store it in a cool, dry place away from interfering items.
Keep the Magnetic Tape Clean
Dust and dirt can weaken the bond between the magnetic tape and the window frame. Periodically wipe both with a damp cloth to remove debris, and ensure they are dry before reinstalling the glazing.
Replace Worn Magnetic Tape
Magnetic tape can lose its adhesive properties over time, especially with high temperatures or frequent reinstallation. Regularly inspect for wear, like peeling or weakened magnetic strength, and replace as needed for a strong hold. You can easily purchase replacement magnetic tape from us if you need to.
For more detail, please see our guide on how to store your secondary glazing to prolong its lifespan. If you have any concerns or questions, feel free to contact us.
| Material | Acrylic |
| Finish | Clear |
| Maximum Sheet Size | 3050mm x 2030mm |
| Available Thicknesses | 3mm, 4mm, 5mm |
| Light Transmission | > 92% |
| Fire Rating | UK Class 3 Fire Rating |
| Water Absorption | 0.2% (24 h, 23oC) at dry state 50 x 50 x 2mm – 40mg to ISO 60, Method 1 |
| Manufacturers Tolerances | +/- 10% plus 0.4mm (e.g. 5mm cast sheet could vary from 4.1mm to 5.9mm) |
| Cutting Tolerances | +/- 1mm |
No, the magnetic tape is not included. You will need to add magnetic tape to your order by selecting the required size tape in the Magnetic Tape dropdown above. When selected the required amount of tape will be added to your cart.
With a large enough gap between the window and the secondary glazing you could see a 4°C improvement in room temperature. This is exactly what Mark from Lancashire has experienced, he recently sent us the results from his personal experiment on the effectiveness of his secondary glazing which he has fitted to his existing double glazing:
"Rather than go to the expense of replacing my old double glazing or installing triple glazing I went for spending under £200 on a sheet of secondary glazing for the sitting room - which is the one room that needs to be kept at a comfortable temperature.
I have just collated the figures for my first month since installing your 4mm glazing sheet in my sitting room. I bought a pair of digital thermometers with which to test the results of fitting extra glazing. One is situated between my original double glazing and the secondary glazing panel and the other on the windowsill inside my sitting room.
On every occasion that I have noted the figures there has been about a 4°C difference between the outside temperature and that between the primary and secondary glazing and about a 4°C difference between the gap and the interior temperature. This shows that the secondary glazing has insulated the room by almost exactly the same number of degrees as my original double glazing does.
We all know how valuable each 1°C is in terms of turning down the thermostat!
Finally, whereas the window side of my room used to be noticeably colder than the centre, the difference between the inner windowsill thermometer and the weather station indoor sensor (mid room) is always less that 1°C and not detectable to me. This would indicate that heat loss in that room is minimal.
When considering the cost of secondary glazing I calculated that if it paid for itself within 2-3 years it was worth it. I only have one month's figures to work on but an indicative 4°C saving means it will reach breakeven point in the winter months of the first year."
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Mark sent us this photo of his secondary glazing set up, as you can see there's an amazing 5.3°C difference between the thermometer inside the room to the one on the other side of the secondary glazing. |
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Secondary glazing can be done with a clear acrylic or polycarbonate sheet, attached into place with a removable fastener such as our magnetic tape, allowing you to remove the secondary glazing during the warmer periods.
This will depend entirely on the size of your window. For a window measuring 635 x 890 mm, which is a fairly common window size in the UK, our 3mm plastic secondary glazing kit would cost only £55.41 - when compared to the cost of buying new uPVC casement windows, labour costs, and a plasterer to refinish the internal areas round the window, you'll be saving hundreds.
We recommend 4mm for secondary glazing. This thickness offers improved insulation properties and enhanced protection against noise and drafts. It is a common choice for secondary glazing in residential buildings and provides a good balance between insulation and affordability.
2mm: Only to be used on very small windows. 2mm offers basic protection but may not provide significant insulation or soundproofing benefits.
3mm: A good budget option for small windows under 800mm, still lightweight and suitable for basic insulation and protection against drafts. It provides better durability than 2mm and more rigidity.
4mm: Our recommended thickness, you'll certainly notice the improved insulation properties and reduction in condensation, noise and drafts. Any window larger than 800mm will benefit from the rigidity of 4mm.
5mm: Thicker acrylic provides the maximum enhanced insulation and soundproofing benefits. It is suitable for areas where noise reduction and thermal insulation are crucial, such as homes located near busy streets or commercial areas. 5mm is ideal for large windows over 1.5m but it will be heavy so you'll need our thicker magnetic tape and a windowsill or wooden baton to rest it on to take the majority of the weight.
Due to the optical clarity that acrylic provides, there’s no noticeable difference between the visibility or light transmission of your single-glazed windows and the results of secondary glazing. Often a preferable alternative to double glazing, particularly for heritage properties, acrylic doesn’t detract from the external character and look of the windows but gives all of the insulating benefits without causing condensation.
When you install secondary glazing into your property, you achieve the same insulating benefits of double glazing such as lower energy bills and improved heat transfer. Secondary glazing can reduce heat loss via windows by around 65% which is 10% more than double glazing.
To attach your glazing to a window, you'll need to take precise measurements using a measuring tape. Measure both the height and width of the window, and don't forget to include the width of the magnetic tape. Keep in mind that windows are not always perfectly shaped, so it's important to take measurements in multiple places to ensure an accurate fit.
Secondary glazing can be very effective at preventing condensation and mould growth on windows in cold climates. However, this does work best if the secondary glazing has a breathable gap between the panes rather than a fully sealed unit. This allows some airflow which helps prevent the build-up of condensation.
As our secondary glazing kits are magnetic, you can simply remove the plastic sheet for quick and easy access for cleaning or extra ventilation.
Delivery depends on the size of your order
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