Why would mould be growing on my alcove walls?

Hi, I have considarable experience with this, it is simply a matter of lifestyle, what I mean by this is the washing, cleaning toilet flushing etc you do in your home adds lots of moisture to the air, the air will hold more moisture when its warm and less when its cold. Consider air molecules as a box thats gets bigger or smaller when the room temperature goes up or down, so imagine your reasonably warm air floating around your house this has lots of moisture in it as its warm and the air 'box is bigger' when this air box meets a cold surfaces it shrinks but the water doesnt so it condenses on the cold surface which as we all know when left will form mould spores. The reason this occurs behind furniture is because very little warm room air touches the wall and the temp stays even lower behind the furniture than another exposed area of the same wall thus warm moisture laden air condenses here more!

Hi there It is condensation, when you put the book case in the alcove you are trapping the moisture and not allowing any air flow behind which is is the best conditions for mould to grow,best way to0 solve is to increase the air flow to these areas, or thermal board the walls to raise the temperature of the walls which will stop the moisture condensing on the cold walls. regards Joseph