Buildings are moisture machines. Occupants, cooking, washing and breathing add litres of water vapour to indoor air every day. Whether that vapour stays harmlessly airborne or condenses into damp and mould depends on temperature, humidity and the vapour-handling properties of the materials it meets. This pillar explains those mechanisms from first principles — because almost every damp, mould and retrofit failure traces back to a handful of moisture-physics fundamentals.
Get these fundamentals right and the rest of building performance falls into place; get them wrong and even well-intentioned insulation and 'damp treatments' make things worse. The articles below build up logically — from dew point and relative humidity, through vapour diffusion and the five ways moisture moves, to surface and interstitial condensation, the modelling used to predict them, and the measurement methods that turn 'the meter says damp' into a real diagnosis.
Why this matters
The single most expensive mistake in damp work is treating the symptom without diagnosing the mechanism: injecting a chemical damp-proof course into a wall that actually has condensation, or tanking a wall that's being rained on. Each moisture mechanism has a different driver and a different remedy. This guide gives you the physics to frame any damp problem correctly — and to understand why measured diagnosis beats guesswork every time.