Why in particular does mould grow in window reveals?

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Besides in the corners of rooms, mould seems most prone to growing on window reveals: But why here, in particular? Surely here the sunlight should provide sufficient warmth, at least during the daytime. A look through the thermal imaging camera will shed some light on the matter: in spite of the sunlight, thermal bridges can also form in this area, and with them comes mould.

The outer edge of the window reveal is one of these thermal bridges. Temperatures drop repeatedly in this critical area which leads to precipitation, especially during the winter months. Moisture levels of between 70% and 85% combined with organic materials which feed mould growth, such as wallpaper or wallpaper paste, is enough for mould to settle down here for good. Read More