We often get called out to help solve mould forming in bedrooms , the average person breathes out 2 pints of moisture a night so this can create a lot of mould if the moisture condenses on cold surfaces.
In older style properties its common to have a curve in the ceiling that’s not insulated so as can be seen in the picture mould has formed on this cold surface.
The lines in the mould are where the joists are as they are warmer so mould will go either side on the colder surface !!!! look familiar ?
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