Benefits of secondary glazing

Secondary glazing offers a range of benefits over both single glazed windows and double-glazed replacements.

Noise reduction

noise pollution

acoustic insulation

Secondary double glazing is an excellent way of reducing noise and sound pollution. Standard secondary glazing fitted over an existing single glazed window could reduce noise by up to 70%. Using laminated or acoustic glass instead of 4mm float glass increases the sound insulation even more.

Many properties in the UK suffer from noise pollution in various forms. This can be traffic noise, trains, planes or airports, or simply the general noise levels that you get in towns and cities. Secondary glazing is the ideal solution as it outperforms modern double glazing at blocking noise. This is because – when it comes to windows – the most significant factor for reducing noise is the gap between panes of glass. Double-glazing relies on sealed glass units, where the two pieces of glass are typically 24mm or 28mm apart. With secondary glazing the two pieces of glass are more likely to be around 100mm or more apart.

The other factor that influences acoustic performance is the glass used. Standard 4mm glass used in secondary glazing will typically give a noise reduction of round 40 decibels (dB). Using different glass can increase this reduction:

  • 6mm float glass (43dB)
  • 6.4mm laminated glass (46dB)
  • 6.8mm acoustic laminated (50dB)

These are approximate figures. Other factors such as distance between glass panes and installation method can affect these figures, but they give an indication of the decibel reduction levels that can be achieved.

Thermal efficiency

Windows are a key area for heat loss in any building, and single glazed windows are particularly poor at preventing heat loss.

Installing secondary glazing can dramatically improve the thermal efficiency of your windows. Even with standard 4mm glass it can halve the amount of heat lost through your windows by improving the U-value from around 4 W/m2K to 2 W/m2K or better.


Typical U-values

Adding thermally efficient low-e glass (such as Pilkington K) improves things even more, bringing the U-value down to around 1.5.


Secondary glazing is not a replacement window, which means that it is not subject to UK building regulations. In turn this means that there is no time-consuming, expensive building control approval process.

Of course, if your property is subject to any specific regulations (e.g. Listed Building Control) you may need approval before fitting secondary glazing.


By providing an additional barrier, secondary glazing can help improve security.

window securityIt is difficult to open secondary glazing from the outside. So even if an intruder gets past the main window, the secondary adds another layer that would take time to get through. This is often enough to put opportunist intruders off altogether.

Add difficult to break safety glass (such as toughened or laminated) and secondary can provide a marked improvement to window security.

Shake, rattle (and roll?)

Old timber windows, particularly sash windows, are renowned for shakes and rattles. They’re draughty, noisy, and allow dust and dirt through. Secondary glazing provides an effective barrier, making the environment inside that much more pleasant.

Environmentally sound

Installing secondary glazing can often be the sound environmental choice, for three reasons:


  1. The improved thermal efficiency mentioned above reduces heat – and thus energy – consumption.
  2. Aluminium uses less fossil fuels in its production than the uPVC used in most modern replacement windows. Also, there is less material in a secondary window than there is in a replacement window.
  3. Repair and reuse! Why condemn your old windows to the landfill site when you can extend their life by installing secondary glazing? And if you ever remove your secondary glazing, aluminium is easy to recycle and in high demand.


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If you’d like to find out more about how your home or building could benefit from secondary glazing, please contact us.