Environmental protective glazing

Stained Glass Windows: Managing Environmental Deterioration, published by Historic England in 2020, defines Environmental Protective Glazing (EPG) as: ‘…the installation of a second layer of glazing (the ‘protective glazing’ on the weather side of the glass), with the space in between ventilated to create a thermal buffer for the historic glazing… ; examples of secondary glazing date back to the very beginning of the 19th century. In the past, EPG was sometimes called ‘isothermal glazing’, but this is a misleading term that does not reflect how the system operates.’

It suggests that: 'For stained glass suffering from serious and otherwise intractable environmental problems, Environmental Protective Glazing (EPG) is a powerful conservation tool, allowing deterioration to be greatly decreased whilst retaining the window in the building. On the other hand, it can also be one of the most challenging interventions, partly because of its aesthetic impact on the building, and partly because of the skill needed to design a well-functioning EPG system. A poorly functioning EPG system that is aesthetically satisfying is not a good solution.'

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