Secondary Glazing

05. Secondary sash windows fitted for noise reduction (Print Room, London Bridge)
23. Secondary sash windows fitted in a commercial project, luxury apartments (Great Portland Street, W1, London)

Secondary glazing (sometimes referred to as secondary double glazing) is a term used to describe the process of installing a second window internally within the inside of a property.

The original window stays untouched. The secondary glazing is fitted to mirror the design of the primary window.

Secondary glazing is a fully installed window that operates independently from the existing window.

It is particularly popular and necessary in listed buildings and those properties found within conservation areas.

Secondary glazing is commonly mistaken for double glazing (or a replacement window).

Double glazing means that the external primary window is glazed with a double-layered glass unit (sealed unit) and is normally separated by a thin spacer. This spacer is normally only a few millimetres thick.

Secondary Glazing can be used for many applications:

  • Reduction of external noise
  • Heat retention / Insulation / Energy efficiency
  • Added security
  • Condensation

This process is common for both residential and commercial applications.

Secondary glazing is an ideal solution as not only is it effective, but it is also aesthetically pleasing and will not draw attention away from a room or beautiful period windows.

Types of Secondary Glazing


City Sound manufacture their own secondary glazing windows. We specialise in aluminium frames only, powder-coated standard white.

However, the frame colour can be matched to any RAL Classic colour. This would of course be a bespoke secondary glazing service, so please be specific when getting in touch.

Aluminium is a strong, quality material to work with. It allows for a window design to be slim and discreet, something that is aesthetically pleasing and will last for a long time with minimal maintenance.

The idea is to install something that does not command attention when entering a room. Our secondary windows are hardly visible.

There are other types of material that secondary glazing can be made with.

We do not supply these:

Magnetic secondary glazing – more of a temporary DIY solution for heat retention. These are normally made of acrylic sheets. Acrylic will of course weather over time, break easily, discolour and scratch.

Timber secondary glazing – An obtrusive solution. A timber window design needs to be thick to be functional and to operate correctly. Timber windows will also need regular maintenance, painting etc.

uPVC secondary glazing – An obtrusive solution.

A uPVC window frame needs to be thick to be functional and to operate correctly. uPVC is also known to discolour.


There are a number of different secondary window styles to choose from in order to mirror the original, primary windows:

  • Sash window
    • Vertical slider; up and down
    • Please contact us to discuss our EASY CLEAN sash design. In most cases, this allows easy access to the full surface area of the glass for cleaning (both front and back).
  • Horizontal slider window
    • Side to side sliding window.
    • These can be two, three, or four-panel sliding.
    • In most cases, the secondary glazing panel can be lifted out for cleaning.
  • Casement window
    • Single or double-hung, hinged unit.
    • Hinged units can be manufactured as windows or doors.
  • Lift out window
    • A secondary glazing panel can be lifted out.
  • Fixed window
    • They are fixed in place and non-removable.

We also manufacture shaped/arched windows – please get in touch to discuss further if you have a need.

01. Secondary sash windows fitted over period windows (Islington, London)
01. Secondary glazing fitted over this Georgian period window; Thermal insulation (Hampstead, North West london)
02. Secondary glazing fitted to perfectly mirror the external window. Arched window above to match the design (Central London)
03. Casement (hinged) windows fitted over this leaded bay window; Thermal Insulation 3
01. Secondary glazing lift out windows fitted over beautiful steel framed windows (East London, E1)

Advantages of Secondary Glazing

Secondary Glazing Noise reduction

Secondary glazing is probably one of the best ways to help reduce the noise coming through your windows.

You might try to draught-proof the surroundings with one of the many products found at your local DIY store, or perhaps change the existing glass in your external window for double glazing.

Maybe even quite simply hang heavy curtains in front of the windows.

It is true to say that all of these will help a little, but unfortunately, the best sound insulation you can expect to achieve using these methods is around 10%.

So be careful not to send out a sizeable amount of money only to be disappointed.

Did you know that over 30% of secondary glazing fitted by City Sound is installed in windows already double-glazed and many of them are in new builds where the soundproofing from the modern double-glazing windows is not sufficient enough?

Why is secondary glazing so effective for noise reduction?

Like all good soundproofing (as in a recording studio, for example), the best results are achieved only where there is an adequate cavity between the two points of contact (i.e., cavity or air gap between the primary and secondary glazed window).

That’s why at City Sound, we always try to install our low-profile secondary glazing system with a sufficient cavity from your existing window to ensure maximum sound insulation.

In layman’s terms: The bigger the air gap (cavity) between your existing window and the new secondary window, the better the level of noise reduction.

Many clients are led to believe that changing an external window to a double glazed window will solve noise issues. We implore you are researching this independently.

With double glazing, the air gap is only a few millimetres.

Adding secondary glazing instead, you achieve a gap far bigger in centimetres. This is a very important difference and key to how much noise you can keep out.

What kind of noise reduction can be expected from City Sound’s secondary glazing?

There are many different kinds of noise pollution you may experience – but let us take road traffic noise, for example.

Fitting secondary glazing with our desired cavity, you can expect a reduction of around 70 –80% in noise levels, and in some cases, as high as 90%.

(Please note that the above guidelines are based on the installation of our own aluminium product, using our unique methods of work, and incorporating our specified glass.)

Thermal insulation & Energy Savings

There are important reasons to reduce energy consumption in our buildings through improved thermal efficiency. In terms of energy saving, windows are the prime area in which heat loss can be prevented.

Single glazed windows are poor insulators, and heat loss is exacerbated if the window does not have effective seals.

The UK & its government have made a commitment to reduce carbon emissions. Buildings account for 44% of the total and are therefore a prime target.

Why secondary glazing for insulation?

  1. Secondary glazing can be fitted to improve thermal insulation as well as eliminate draughts. Efficient secondary glazing glazed with the correct type of glass can improve the thermal performance of a window by more than 60%.
  2. Secondary glazing can reduce condensation.
  3. Secondary glazing will help make your home more energy-efficient and help save you money on your fuel bills. The cost of heating homes or buildings is rising all the time, so the sooner you fit secondary glazing, the sooner you can benefit.
  4. The use of secondary glazing can help meet the standards set in Part L of the Building Regulations.
  5. Energy Performance Certificates will define a building’s Energy Rating and become a factor in property valuations in times to come.
04. Horizontal siding, 2-panel window fitting for noise reduction (Kensington, London)
17. Sliding windows fitted to a Grade II listed house; Thermal Insulation (Kent)


Domestic burglaries are on the rise. However, they tend to be spontaneous and not planned or professional attacks.

The easiest way to gain access to a building is through doors and windows. Properties with original single-glazed windows or older double glazing are often seen as easy targets for burglars.

They are more vulnerable to burglary and more likely to be broken into.

Secondary double glazing can add an extra layer of security to any commercial or domestic property that requires it.

Secondary glazing acts as a second barrier from the outside that can stop even the most determined thieves from getting in. Secondary glazing is nearly impossible to open from outside.

The frames are made of tough aluminium and tightly fixed to resist forcible removal. The use of laminate-type glass will make matters even more difficult for any possible intruders.

Secondary Glazing for Listed Buildings

When a building has been listed it is protected by law and Listed Building Consent might need to be obtained before any changes are made to it. Repairs that match exactly may not need consent, but examples of work, which may do include changing (or adding) windows and doors, as the effect of any repairs are not always straightforward.

Sash Windows (Vertical sliding)

Commonly called “Vertical sliding sash windows” within the industry, sash windows are by far the most common window style. For this reason, of course, our secondary glazing sash style windows are equally as popular.

Consisting of two panels (top and bottom) that slide up and down, our sash windows are counterbalance with pre-tensioned springs to hold the weight of the panels. This enables the window to be opened to any position, also allowing for the panels to be operated with minimal effort.

Fixed Lift Out

An alternative to screw fixed units, fixed lift out windows have a removable glass panel that can be easily lifted out of the master frame to facilitate access to the external windows.

This style of window is often used on external windows that are very rarely used or in air-conditioned offices where cleaning between the windows needs to be facilitated.

Horizontal Sliding Windows

The most versatile of all the styles available, horizontal sliding windows (side to side sliding) can be manufactured with 2, 3 or 4 sliding panels. This style of secondary glazing is a perfect match for Crittal windows. The individual sliding panels slide with immense ease, allowing unobstructed access to the external windows.

All our windows sections are made of aluminium, powder-coated white as standard. Frames can however be customised to a different colour or finish to match surrounding décor.

Casement (Hinged) Secondary Glazing

A versatile, efficient and inexpensive style of secondary glazing that can be side or top hung. This is a strong system with slender sightlines, allowing full and easy access to the outer windows or doors.

With minimal dust ledges and a tight seal, this style of window is often favoured by hospitals, surgery rooms or laboratories.

Service Areas

We have provided secondary glazing solutions to the whole of London (within the M25) for the last 53 years. Below are some of our key areas we do most work in however, we do cover all of London. If you are looking for secondary glazing near you please get in contact for a free no-obligation quote.

  • Aldgate
  • Aldwych
  • Angel
  • Bankside
  • Barbican
  • Barnsbury
  • Battersea
  • Bayswater
  • Belgravia
  • Bermondsey
  • Blackfriars
  • Bloomsbury
  • Brixton
  • Camden Town
  • Canonbury
  • Chalk Farm
  • Charing Cross
  • Chelsea
  • Chinatown
  • Clapham
  • Clerkenwell
  • Covent Garden
  • De Beauvoir Town
  • Earls Court
  • Elephant and Castle
  • Farringdon
  • Finsbury
  • Fitzrovia
  • Fulham
  • Hammersmith
  • Holborn
  • Holland Park
  • Hoxton
  • Islington
  • Kensington
  • King’s Cross
  • Knightsbridge
  • Lambeth
  • Lisson Grove
  • Maida Vale
  • Marylebone (also St Marylebone)
  • Mayfair
  • Millbank
  • Newington
  • North Kensington
  • Notting Hill
  • Oval
  • Parsons Green
  • Pentonville
  • Pimlico
  • Primrose Hill
  • Sands End
  • Shoreditch
  • Soho
  • Somerstown
  • South Kensington
  • St James’s
  • St Giles
  • St John’s Wood
  • St Luke’s
  • St Pancras
  • Stockwell
  • Temple
  • Tower Hill
  • Vauxhall
  • West Brompton
  • West Kensington
  • Westminster
  • + Other Areas

Secondary Glazing FAQs

What is secondary glazing?

Secondary glazing is an alternative to double glazing, whereby an additional supplementary pane of glass is installed alongside another single glazed pane of glass.

Will secondary glazing keep my home warmer?

Yes, secondary glazing is very effective at retaining warmth in your home.

What if I struggle with noise pollution from outside? Will secondary glazing help soundproof my home?

Secondary glazing is a very good barrier against unwanted noise, in fact considerably more effective than double glazing. The independent planes of glass, with a slightly wider space between them, act as a protection against any manner of noise which may be bothering you, be it traffic or even noisy neighbours.

What about if I live in a period or listed property?

Secondary glazing is the perfect solution for those who want to upgrade their windows but want to retain the character and charm their existing windows afford their home. By introducing the addition of a supplementary pane of glass inside of the existing windows, all the benefits such as noise reduction and heat retention can be enjoyed, without affecting the appearance and charm of your period windows.

Can I use secondary glazing with my sash windows?

Secondary glazing can be a solution for all manner of window styles, including sliding, fixed and casement. Sash windows are an incredibly popular style and can of course benefit from the installation of secondary glazing. A good installer will always ensure the secondary glazing panes exactly match the external windows, so they maintain their attractive appearance.

Is secondary glazing expensive?

Secondary glazing is a very cost-effective means of upgrading your windows. Not only is it cheaper, but much less intrusive to install when installed by a professional.

Will secondary glazing help protect my home?

Not only will secondary glazing help protect your home from the elements and from unwanted noise, but it can offer an increased level of security. With the addition of a further separate window behind the existing one, you introduce an added layer of protection and complication to deter possible thieves.

City Sound Window Styles

With a number of styles to choose from, it is always important to pick the right one that suits the external windows. Mirroring the original windows and not adding site lines is very important, as it ensures the secondary glazing blends in well with its surroundings and is as unobtrusive as possible. If you are living in a period home, this is even more of a concern, as you do not want to detract attention away from the charm the windows lends to the property.

City Sound Secondary Glazing

City Sound Secondary Glazing - Commercial ClientsCommercial Clients

Dealing with commercial clients and projects needs special care and know-how. We are a flexible, friendly company with years of experience able to deal with any and all requests from this sector.

City Sound Secondary Glazing - Residential ClientsResidential Clients

Offering a professional, one to one service to our residential clients. Practical surveyors and engineers makes working with us a pleasure. A dedicated after-sales service will make sure you are always in good hands.

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