Secondary Glazing for Listed Buildings & Conservation

What is an historic or traditional building? English Heritage gives the following definitions:

  • Solid wall construction
  • Bay window
  • Sash window
  • Built without a damp-proof course
  • Single glazing
  • Probably built before 1919

These are the early traditional homes that form so much of our heritage, many of which are now Listed Buildings &/or in Conservation Areas, with original period single glazing of all types. These include:

  • Georgian casement & sash windows
  • Victorian casement & sash windows
  • Edwardian windows & doors
  • Crittall-type steel windows & doors

The installation of discreet secondary double glazing for Listed Buildings, Conservation Areas & all types of heritage & historic windows is considered the best, and in most situations the only acceptable treatment for:

  • Creating comfortable living conditions
  • Reducing energy usage
  • Cutting CO2 emissions
  • Conserving period properties

Apart from the strict regulatory controls on upgrading & improving Conservation Area & Listed Building windows, practical common sense also makes secondary double glazing the product of choice.


Why Use Secondary Glazing in Period Properties?

During the last few decades of the 20th century, modern replacement windows spoiled the appearance of thousands of old Georgian, Victorian, between & post war houses, flats and apartment blocks.

Additionally, poorly designed replacement windows have actually damaged many older properties which were not designed to be completely sealed up. This causes problems such as:

  • Reduced ventilation
  • Trapping humidity
  • Creating condensation traps


All buildings need regular changes of the internal air to avoid:

  • Damp & mould infestation
  • Condensation on windows & other surfaces

This is particularly relevant for our Georgian & Victorian housing stock as these older properties need more frequent air changes than modern ones.

Modern double glazed windows do not enable an old property to “breathe” sufficiently in order to avoid problems and continue in a good, sound condition.

As a rule of thumb, a traditional building needs to be ventilated at a rate of 0.8 to 1.0 complete air changes per hour. This is double the amount needed for a modern building.

Since natural ventilation rates in many older buildings actually exceed this value, secondary glazing is normally very beneficial in reducing the rate & improving the thermal insulation.


Why Secondary Windows - Why Not Replace Them?

The reasons for using a secondary window rather than a complete new window in traditional properties can be summarised as follows:

  • Regulatory control – generally specified by Planning & Conservation Officers
  • Aesthetics – secondary glazing does not spoil the appearance of an older property
  • Protection of the fabric of the building
  • Protection of the value of the property
  • Costs of secondary glazing will be considerably less than replacements
  • Environmental costs of secondary glazing are far lower than replacements, in terms of  the manufacturing energy usage and the disposal of the original windows
  • Most old windows can actually be repaired when necessary, frequently they have been needlessly replaced
  • Good quality secondary double glazing will be virtually invisible externally and extremely discrete internally 
  • Conservation - to survive both structurally and financially, old buildings need to remain in use but with improved thermal and noise insulation, as well as better security
  • The value for money will be greatly increased by installing secondary glazing due to the reduced costs of upgrading
  • Well maintained and insulated period properties are increasingly sought after
  • Reduced energy costs will quickly return the investment


The Heritage Range

In addition to our standard range of discreet secondary double glazing, we also have a complete suite of secondary windows especially designed for period buildings. Our Heritage Range is designed specifically for older, traditional properties. It is unobtrusive but very effective, providing:

  • Exceptional heat insulation
  • Maximum noise reduction
  • Concealed multi-point locking
  • Clean, minimal site lines

Fixing methods are also concealed and a sympathetic range of finishing trims and mouldings assists in blending the secondary glazing into traditional surroundings. 

Frames can be manufactured out of square, arched, radiused or curved to achieve the best possible end result.

The full RAL colour range is available for colour matching as well as a woodgrain effect. Decorative paint finishes can also be applied, so that each secondary window can be matched to either the existing or proposed décor.



Our secondary windows are installed in all types of period buildings. Secondary windows help to improve:

  • Heat insulation - can comply with Document “L” requirements
  • Sound insulation - the most effective product for eliminating outside noise
  • Control of condensation
  • Security

Secondary Glazing Service

We have worked in Listed Buildings and Conservation areas for over 30 years and we can therefore give an expert service from initial contact and advice, through to the finished job. This is all supported by our unique knowledge base, depth of experience and most of all our expert glazing department.

Please call us for advice on any aspect of secondary double glazing for traditional properties. We can provide specifications for your planning application. Please request a site visit either for an initial consultation & advice, or for a detailed specification & quotation. We also also provide bespoke secondary glazing windows developed for larger individual projects.