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Secondary Glazing

What is it and why would you use it?

In the UK, there are almost 10,000 Conservation Areas, many of which restrict the changes that can be made to the existing fenestration (i.e. windows). In some cases, this means single glazed windows must be retained, even if they are inefficient and uncomfortable to live with.  This is where secondary glazing can make a huge difference.

Calabria Road

Calabria Road – One of 10,000 Conservation areas in the UK


Secondary glazing is an additional window system which can be retrofitted to existing buildings to improve:

  • Heat insulation
  • Sound insulation
  • Security
  • Solar protection

It is typically fitted independently of the existing window system.  In Conservation Areas, the surrounds/ glazing bars should be lined up to match the existing windows  – so the secondary window is invisible from the outside.  Wherever possible, it will fit within the existing opening and will not infringe on the existing window joinery and architraves.  However, this is not always possible.  Nevertheless, modern designs tend to be much slicker than the clunky versions many people are familiar with.

Windows with secondary glazing

Secondary Glazing by Selectaglaze: Closely matching the existing windows


In residential projects, noise and heat control are key factors in fitting secondary glazing and we can see why-

  • A single glazed window will only reduce noise outside by 20db,
  • Good quality double glazing reduces the sound by 34db
  • Secondary glazing can increase the sound insulation by around 45db. In bustling areas such as London, this reduction in noise can make a huge improvement to your quality of life at home.

Equally, secondary glazing can reduce heat loss through a window both through additional glass and by sealing air gaps in the current glazing.

Other more commercial features of secondary glazing include additional security including bomb blast mitigation (yes really!!) and environmental control, which is particularly useful to protect artworks from damaging UV light.

Highbury Corner

Traffic, Roadworks, Football fans… London can be a noisy place



If you’re thinking about how secondary glazing could work for you, here are some considerations to ensure you get the right type/ fit for your property:

  • How is the window operated? Can it open and be fitted in such a way which allows the existing window to open at the same time?
  • Can it be thoroughly cleaned? Most suppliers will design the glazing to ensure all parts of the existing and new glazing are accessible for cleaning.
  • Is the style/ profile acceptable for planning controls?
  • Does the additional glazing affect your current window coverings? If so, what will you change them to and how will you fit them?
  • Cost – cost for secondary glazing can be high at the outset but remember to factor in the savings you will make over the years in reduced energy bills as well as the value of a quieter, more restful environment. Secondary glazing is also usually less expensive overall than having bespoke periodic windows replaced.
Arched secondary glazing

Opening details are an important consideration


If you’re considering renovating your windows, or are unsure on the rules that apply to your property- get in touch.  We often work on Listed or Conservation Area properties so can help advise on the solutions that will work for your home.

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