Do protective glazing systems enhance the thermo-hygrometric stresses of stained glass windows?

The European multidisciplinary VIDRIO project carried out a microclimatic study of three churches (Saint Urbain Basilica in Troyes, Sainte Chapelle in Paris and Cologne Cathedral) noted for their ancient and historically important stained glass windows. The monitoring of the environment indoor, outdoor and in the interspace between ancient window and protective glazing was performed, aimed at assessing the impact of the use of protective glazing on the environmental conditions of the ancient windows. The results obtained confirm that the protective glazing protects the ancient stained glass windows from outdoor environmental attack and from the risk of condensation. However, the impact of the protective glazing on the microclimatic conditions of the windows depends heavily on the technical characteristics of the system installed which generally reduce the impact, but in some cases can aggravate thermo-hygrometric stresses on the protected window.