Condensation

There is always some water vapour in the air, which you cannot see.

Condensation is caused when moisture held in the air meets a cold surface like a window or wall and condenses into water droplets.

Condensation gets worse when the house is colder, whether it is raining or dry and it does not leave a 'tide mark,' unlike other causes of damp.

It often results in black mould growth on walls and other surfaces or you can see actual water droplets. It is usually worse in corners, on or near windows, in or behind wardrobes and cupboards and on North facing walls.