Secondary Glazing Across the UK

In most cases, we recommend a thickness of 4mm for secondary glazing with flexible installation. The insulating tape and glazing clips will fit perfectly on secondary glazing of this thickness. We recommend 4mm for fixed installation on windows up to 2 metres long, and 5mm for fixed installation on windows between 2–3 metres. Thinner or thicker sheets may not insulate adequately due to fitting issues with standard tape and clips.

In most cases, we would recommend going for thicker secondary glazing — 4mm or even 5mm for larger window frame setups. 2mm offers basic protection and is only suitable for very small windows. 3mm is a budget option for smaller windows under 800mm. For most residential windows, 4mm provides the best balance of insulation, rigidity, and cost.

There is no single best type — the right choice depends on your windows, property type, and primary goals. Aluminium sliding units are popular for most homes. Acoustic glass with a 150–200mm air cavity provides the best sound insulation. For listed buildings, lift-out or magnetic systems are often most appropriate.

Secondary glazing is installed on your internal window frame and consists of panes of glass in a slim aluminium frame fastened to your window reveals or the inner face of your window frame. Sliding, hinged, or lift-out units are available. Once fitted, our unobtrusive solutions are scarcely detectable from inside or outside — ideal for maintaining the external appearance of period and heritage properties.

Secondary glazing, when properly specified and installed, will outperform all other forms of glazing — including modern triple-glazed windows — for sound insulation. In most cases, we recommend acoustic glass and an air cavity of no less than 150mm–200mm between the two panes of glass to achieve up to 80% acoustic performance. This makes secondary glazing the best solution for properties near airports, busy roads, industrial estates, or city centres.

Acrylic secondary glazing is generally easier to work with and 17 times stronger than glass by weight, with near-perfect optical clarity. It is also lighter. However, acrylic can scratch more easily than glass, so we recommend cleaning it with a gentle anti-static detergent. Some customers prefer glass — neither is definitively better. Contact us to discuss which is most suitable for your situation.

Yes — secondary glazing will save you money on heating. With a large enough gap, you could see as much as a 4°C improvement in room temperature. That translates to 4°C that you don't have to heat with your central heating system, saving you money and reducing the time your heating needs to be on. Energy efficiency savings of up to 60% are achievable.

To measure secondary glazing, use a tape measure to record the height and breadth of the frame to which you are connecting the glazing. Note that not all windows are perfectly square — measurements must be taken at multiple points for an accurate result. Alternatively, simply send us a photo of your window with approximate dimensions, and we can advise and quote without visiting your property.

Secondary glazing prevents condensation from forming on the inside of your windows by reducing the temperature difference between inside and outside. In most circumstances, installing secondary glazing will remove all condensation from your windows. This is particularly effective in older properties with single-glazed windows where condensation is a chronic problem.

Yes — secondary glazing is the preferred solution for listed buildings and conservation areas. Because it is fitted internally and does not alter the external appearance of the window, it is almost always permitted without planning consent. We have extensive experience working on Grade I and Grade II listed properties, period homes, and conservation area dwellings.