Getting glazing right

Zoe Williams of Selectaglaze discusses why housing managers and landlords should use secondary glazing and the specific considerations to bear in mind

There are many misconceptions about secondary glazing, also known as secondary double glazing, but well designed and carefully engineered systems are available that improve the performance of windows in almost any style of existing building as well as new build developments in need of significant noise insulation. In the case of a listed building, there are often restrictions on what can and can’t be replaced, with windows generally having to remain in their original state. The charm and character that period sash windows bring to the face of the building can be offset by an unpleasant environment for the user if left in a poor condition. With thin glass, rattling frames and poor sealing of the surrounds, the windows will be draughty, lose heat, increase energy consumption and allow noise to disturb the peace of an interior. Another factor to consider is the security that thin glazed windows provide – not a great deal. Secondary glazing is a very practical way of upgrading these architectural gems and, as it is regarded as a reversible adaptation, is almost always accepted by conservation officers.

So how can secondary glazing help?

It’s warmer: over time buildings move, which can cause cracks and distortion of window frames leading to draughts and heat loss, often with significant differences in temperatures across a room. Installing Secondary glazing, fitted with high performance seals and designed to cover the whole of the external window frame, will reduce U-values by 40 – 50 per cent with standard glass and up to 65 per cent with a low emissivity glass. A significant reduction in draughts helps to even out the room temperature leading to a more comfortable environment. It’s quieter: installing secondary glazing is the most effective method of dealing with noise problems. The air gap created between the primary and secondary glazing is fundamental, as it decouples the panes of glass, limiting sympathetic resonance and hence the passage of sound. A reduction of 45 dB can be gained with a cavity of 100 mm and higher reductions are possible with deeper cavities and heavier glass. It’s safer: secondary glazing frames with accreditation to Secured by Design provide a good level of intruder resistance. Higher levels are achieved with products certified to Loss Prevention Standard LPS 1175. These offer similar protection to heavy gates and grilles.

Which supplier do I use?

There are many reputable secondary glazing suppliers with different systems – each has their own merits. However, when comparing and deciding which to use, some points to consider are:

  • Does the supplier have test reports or figures to back of their claims of performance? With noise it is best to check the sample size tested. If relatively small, it is likely to pass a test, however it may not perform well when used in a large opening. With security, test certificates may be required by insurers
  • How are the frames fixed? Ideally you want the secondary glazing fixed to a discreet timber sub frame as this will ensure all gaps that air can pass through are closed providing maximum benefit
  • Operation of sliding sashes – does the secondary glazing allow full access to the primary windows when opened? Best practice is to install a system which facilitates this to ensure the original windows can be easily reached for future maintenance and cleaning
  • Can a sample be provided to see how it looks aesthetically? These will often be corner samples or carry size samples, which can be sat in the reveal to show the size of the sections and give an idea of the sightlines
  • Do the systems need to be removed in summer months? If so, you then have the added issue of finding storage.

Zoe Williams is head of marketing at Selectaglaze