Secondary Glazing - Quieter & Warmer

Secondary GlazingSecondary Glazing can match the benefits offered by new windows, whilst retaining the character of your home. Whether it’s for the noise reduction, energy efficiency or increased security Treforest Glass Secondary Glazing will provide you with years of trouble-free service.

Secondary Glazing offers the most effective sound insulation –significantly outperforming double glazing. Our windows can reduce noise levels by up to 80 percent (54dB), whilst reducing heat loss by up to 65%.

Our discreet systems can be quickly installed into most window recesses, and are generally approved for use in most conservation areas and listed buildings. 

Up to 80% noise reduction of Treforest Glass Secondary Glazing. 


  •  Up to 65% heat retention
  • Enhanced security
  • Balanced ventilation to reduce condensation   
  • Over 200 RAL colours available

The problems associated with traditional sash windows tend to be similar whatever the type of property you have, whether it is a country cottage, a Victorian terrace, or a mansion flat. These properties tend to be old so are poorly insulated throughout, with the large single glazed sash windows being a major source of heat loss.

The issues don't just stop at heat loss, as the construction & age often lead the windows to be draughty and to rattle in the wind. Many sash windows also suffer badly from condensation.

These windows are also less secure than modern equivalents posing a security risk - they are easy to break into even without breaking the glass itself.

Finally, traditional sash windows are renowned for being noisy. 

Replacing traditional sash windows can be tricky as often the building may be listed or under conservation orders so cannot be replaced with modern double glazing. Replacements often don't have the same look as the original window, leaving the owner unable to replace at all.

Secondary Glazing can eliminate these problems, seeing improvements to insulation, security and noise, all while maintaining the original look of the property.

The key to selecting Secondary Glazing is to choose a product that suits the property owner’s requirements and has the lowest visual impact.

There are four main types of Secondary Glazing:

1. Lift out units: These units are used where the primary window is fixed or where a customer seldom requires access to open the window for ventilation.

2. Hinged Units: These units are generally used with casement/hinged primary windows

3. Vertical Sliders: These units are normally used on vertical sliding sashes with the meeting rails aligning with the primary window meeting rail

4. Horizontal Sliders Normally used in conjunction with either sash or casement windows where full access is required and where there is sufficient space internally to open the casement secondary glazing

To achieve a higher acoustic performance, a minimum gap of 100mm should be achieved between the primary window glazing and the Secondary Glazing. The optimum desirable gap is 150mm. The installation method will depend upon the depth of the window reveal. If the reveal is insufficient to achieve the minimum 100mm gap, then the window will require boxing out to the required depth. Our Surveyor will advise on this and any other issues at the time of survey.

Noise ReductionThermal InsulationInstallationsProductsListed Buildings

Secondary Glazing Window Gallery   



      Secondary Glazing Brochure                        Secondary Glazing - Technical Data Sheet

Secondary Glazing Brochure               Technical Data Sheet