Where the water comes from
Condensation forms when moist indoor air meets a cold surface. Infiltration is water entering from outside or from an installation. The fix for one does nothing for the other, so telling them apart matters.
Clues that point to condensation
Damp and mould-like growth in cold corners, behind furniture, around windows and on north-facing walls, worse in winter and when the home is closed up, often suggest condensation. Surfaces may be damp while the material just behind is relatively dry.
Clues that point to infiltration
Damp that follows rain, appears below terraces, bathrooms or pipes, or shows tide marks and salts often points to infiltration. Moisture measurements, timing and pattern together usually tell the story.
