Condensation is a common cause of dampness and is the change of the physical form from the gas phase (water vapour) into the liquid (condensed) phase, and is the reverse of evaporation. It can also be defined as the change in the state of water vapor to liquid water when in contact with a liquid or solid surface.

 A common example of this, especially in cooler climates, is when the bathroom mirror. “steams up”  when the water vapour created by the shower condenses on the cooler face of the mirror. The same effect is witnessed in other rooms when walls have retained coolness due to the season and the rooms warm up when inhabited. Water vapour in this warm air changes back into liquid form when in contact with the solid surface of the cool walls. Condensation can be distinguished from rising damp even without a moisture meter as it has no height barriers and if it is evident higher up walls it cannot be attributed to being rising damp as rising damp does not usually rise above a metre in height.

Condensation when not treated can lead to mould growth on walls, furniture and clothing. Mould and its spores (‘seeds ’) will cause a musty odour and can sometimes give rise to health problems. Condensation will predominantly occur on cold walls and floors, but sometimes will occur in roof spaces and in subfloor areas where there is a suspended floor. Timbers in these areas could be susceptible to damage by dry rot, wet rot and white ants.