Vapour is the cause of mould and condensation. It is the root case of unwanted dampness 85% of the time in UK.
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Water evaporates to form vapour. Vapour moves by diffusion from higher concentrations to lower concentrations across the vapour gradient (measured as as kPa of vapour pressure).
Dew point is an useful proxy for vapour pressure. See our calculator for:
- dew point,
- relative humidity,
- surface humidity (unique)
- daily mould and condensation risk forecast (London).
Tips for vapour
- Vapour condenses when there is excess vapour or a drop in temperature, like an ice cold drink on a warm day.
- Vapour results from:
- Insufficient ventilation of vapour from a source such as; a shower, drying clothes or boiling water.
- Heat imbalance, either:
- across the property, such as an exposed cold pipe, poorly insulated wall, ceiling, eaves or floor,
- across the course of day, such as by turning the heating off at night and closing windows.