Secondary Glazing vs Double Glazing: Which Is Right for Your Home?

Currently, secondary glazing is not directly recognised in the Standard Assessment Procedure (SAP) used to calculate EPC ratings. This means installing secondary glazing will not improve your EPC certificate, unlike replacement double glazing which is fully credited. This is a known limitation and there are calls to update the SAP methodology to include secondary glazing.

Yes, DIY secondary glazing kits are available from around £60-£150 per window. These typically use magnetic strips or clip-in acrylic panels. Professional installations use aluminium-framed glass panels and cost £200-£500 per window but deliver significantly better thermal and acoustic performance. DIY kits are a good budget option for renters or as a temporary measure.

It can reduce condensation on the original window by keeping the cavity air warmer, but only if the secondary panel is well-sealed. If moist room air penetrates the gap, condensation can form on the cold original glass. Proper sealing, cavity ventilation and room ventilation (e.g., extractor fans in kitchens and bathrooms) all help prevent this.

No — secondary glazing is an internal improvement and does not require planning permission, even in conservation areas or on listed buildings. However, if your property is listed, it is good practice to notify the conservation officer, as some councils prefer to be informed of any works to listed buildings.

Yes, and this is one of the most common applications. Vertical sliding secondary panels are available that mimic the operation of the original sash window, allowing both panes to be opened for ventilation. Horizontal sliding, hinged and lift-out options are also available depending on access requirements.

With a gap of 100mm or more between the original window and the secondary panel, secondary glazing can reduce noise by 35-45 dB. Specialist acoustic secondary glazing with laminated glass can achieve up to 50 dB reduction. This significantly outperforms standard double glazing (25-30 dB) because the wider air gap is more effective at dampening sound.

Well-installed secondary glazing is virtually invisible from outside because the secondary panel sits behind the original window and its frame is concealed within the reveal. From inside, the additional frame is visible but modern systems use slim aluminium profiles (as narrow as 20mm) that are discreet and can be colour-matched to the existing frame.

Most secondary glazing systems are designed for easy removal or opening to allow cleaning of both surfaces. Hinged panels swing open, sliding panels can be lifted out, and magnetic panels simply detach. Fixed panels are the most difficult to clean and are best avoided unless in inaccessible locations.

Yes, adding secondary glazing to double-glazed windows is sometimes done for extreme noise reduction (achieving 45-55 dB reduction). This is most common in properties directly beside motorways, railways or airports. The thermal benefit is more modest as double glazing already performs well, but the acoustic improvement can be dramatic.

Yes, significantly. Even before considering the thermal insulation benefit, secondary glazing creates a physical barrier that blocks draughts from the original window. For draughty sash windows where the original cords and seals have deteriorated, secondary glazing can transform comfort levels immediately.