Secondary Glazing


Secondary glazing cuts heat loss and reduces noise, making your home, office or building a more comfortable place to be. It’s cost-efficient, can reduce your energy bills, and is installed without touching your existing windows or changing the character of your building.

Secondary glazing is a lightweight aluminium window fitted inside of your existing window. It provides an alternative to ripping out old windows and replacing them with modern double-glazed versions.

Secondary glazing is designed so that its bars and sightlines exactly match those of the window it is fitted to. This means that you can’t see it from outside of the property. It has opening sections that match those on the original windows, so it doesn’t get in the way when you want to open your windows.

Fitting secondary glazing to your existing windows provides many benefits, including conservation and cost.

Where to use secondary glazing?

Any period building with original windows is a prime candidate for secondary double glazing. Your building may be listed or located in a conservation area. Or you may just love your original windows and not want to replace them. Whatever the reason, there are many thousands of UK buildings where replacing original windows would be either insensitive or forbidden.

Yet many original windows have an inherent problem. If they are more than 30 years old, it’s likely that they are single-glazed. Single-glazed windows are cold, draughty and terrible at stopping heat from inside the building escaping. And with today’s rising energy costs, that makes them expensive.

Secondary glazing solves this problem by adding a second, unobtrusive window inside the original. This creates a double-glazed effect without having to alter the existing windows in any way.

Cost & convenience

It is usually much cheaper to fit secondary glazing than it is to replace your original windows with modern ones. On top of that, ripping out old windows is time-consuming, messy and often disruptive. In short, adding secondary glazing is a cheaper, hassle-free option.

Secondary glazing is simpler to manufacture and easier to fit than modern double-glazing. It uses far fewer raw materials, and you don’t have to touch the existing windows to install it.

Add all that together, and secondary glazing provides a far more cost-effective solution.

Benefits of secondary glazing

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

Noise reduction

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.

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.

It 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.

So why not contact us to get a free, no-obligation quotation from a member of our friendly team.

Brochure Downloads

Secondary Glazing Brochure

Pilkingtons Texture Glass Brochure