Some of the historically painted windows in the Church St Mary in Rostock had been saved but partly damaged during the 2nd World War. Now they were restored with the aid of “Deutsche Bundesstiftung Umweltschutz (DBU)” and they got an external additional protection window with a space of 80 mm to the old one. This protection window is tight in its led-joints between the glasses and with a new developed led-lip to the brick-wall. The gap between the two windows is ventilated to the interior of the church by upper and lower openings of 100 mm inclined apertures. While restoration work, several sensors could be installed from exterior and interior scaffolds in 30 m height at different points of a northern and southern window. They are: • Thermo-couplers for air and material temperatures • Combined hygro-thermal sensors for air • Anemometers for airspeed in the gap of the windows • Differential air pressure meters between interior, gap and exterior • Collected water at the bottom of the Windows • Manual brick humidity sensors The measured datas were collected every hour on a computer on top of the vault over one year and were added by weather data from the “Deutsche Wetterdienst” in Warnemünde. Before starting the measurement the air-tightness of the windows had been tested with a modified blower door. Before starting and after finishing the microbiological impact of the glasses has been checked. The results of the monitoring proofed, that • the protection window is sufficient tight • the ventilated gap between the windows causes that the interior historic painted window has nearly the same temperature as the interior air. Temperature differences causes convection and temperature compensation. • the risk of condensation on the interior window is low. Microbiological impact which was found after 1 year was not vital.