What is Secondary Glazing?

Secondary glazing is an additional window system installed on the inside of your existing windows. Rather than replacing your original frames, a discreet secondary pane is fitted internally, creating an insulating air gap between the two layers of glass.

This extra layer significantly improves thermal insulation, helping to reduce heat loss and lower energy bills. It also provides excellent sound insulation, making it an effective solution for homes and buildings affected by traffic, aircraft, or general urban noise.

Secondary glazing is particularly popular in period properties, listed buildings, and conservation areas where replacing original windows is not desirable or permitted. Because it is installed internally, the external appearance of the building remains unchanged.

Secondary Glazing – High-Performance Insulation Without Window Replacement

Secondary glazing is a smart, cost-effective way to dramatically improve the performance of your existing windows without replacing them. Installed discreetly on the inside of your current frames, secondary glazing adds an extra pane of glass that creates a highly effective insulating air gap.

Manufactured by Granada Glazing, Fortis secondary glazing systems are engineered to deliver outstanding thermal insulation, noise reduction, and energy efficiency, making them an ideal solution for residential, commercial, and heritage properties.

Reduce Heat Loss & Lower Energy Bills

Secondary glazing significantly improves thermal performance by reducing heat loss through windows. By trapping warm air inside, it helps maintain a comfortable indoor temperature and can noticeably reduce heating costs — a practical upgrade for energy-conscious homes and businesses.

Outstanding Noise Reduction

If you’re affected by road traffic, aircraft, railways, or city noise, secondary glazing offers exceptional sound insulation. The additional pane and air gap work together to cut noise levels, creating a quieter, more peaceful interior environment.

Ideal for Period & Listed Buildings

Because secondary glazing is installed internally, it preserves the external appearance of your property. This makes it a preferred choice for listed buildings, conservation areas, and period homes where replacement windows are restricted or undesirable.

Discreet, Durable & Easy to Use

Fortis secondary glazing systems by Granada Glazing are designed to be slimline, robust, and easy to operate. They blend seamlessly with existing windows while improving comfort, reducing condensation, and enhancing overall performance.

A Cost-Effective Alternative to New Windows

Secondary glazing delivers many of the benefits of double glazing at a fraction of the cost — without disruption, structural changes, or planning complications.

Choose Fortis secondary glazing for a proven, high-performance solution that enhances comfort, saves energy, and protects the character of your property.