Secondary Glazing Systems


Whether you want to improve your building's performance or reduce acoustic transfer through the glass component of your building then Thermosash secondary double glazing could provide the solution.

Thermosash secondary double glazing has been designed to combat the widest possible range of thermal and acoustic problems. Thermosash have installed over 5000 units in New Zealand since introducing them in 1973.

For optimum acoustic performance of secondary double glazing use a glass which differs in thickness by at least 30%, (e.g. 4mm + 6mm + 10mm). Sound reduction will improve with increased glass thickness (particularly at higher frequencies) due to the greater mass involved.

Thermal Performance Benefits

The insulative efficiency of an IGU is largely determined by the thickness of the space betwen the two sheets of glass and whether this space is filled with air or a gas such as argon or krypton. Should the space between be too little, this provides a conductive heat loss between the panes whereas if it is too large, a convective current can begin to circulate causing heat transfer also. Generally the gap is between 16-19mm. As the separation reduces heat gain or cooling from the transfer of cool surfaces - the technology also works in limiting heat loss from the internal environment.

As one of the largest single running costs of a commercial building is attributed to the conditioning of air (heating or cooling) commercial double glazing can provide significant energy savings to almost any project.

Acoustic Benefits

Increasing the width of cavity produces an increase in sound insulation but not pro rata. Beyond a spacing of about 200mm the incremental acoustic improvement is small and, generally, an expensive unit to install due to typical existing reveal depths. Sound reduction will increase with the use of laminated glass, due to the vibration dampening effect of the PVB or by lining the cavity with sound absorbant insulation material, generating sound reduction of 10db (50%) is generally quite achievable with this product, based on limitations of existing building in conditions.

Performance / Testing

  • AS/NZS1170 (Structural Design Actions)
  • NZS4223 (Glazing in Buildings)


The standard warranty is 5 years from the date of practical completion for these products. This covers workmanship and weather tightness, providing the subcontract includes fabrication, installation and glazing of all components.

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