Summary

Condensation in dwellings occurs when warm moist internal air comes into contact with cold inside surfaces, or with cold air or surfaces within the structure.

With improved thermal performance and air tightness in new and existing buildings, the risk of damage from condensation has increased. Most surface condensation is largely caused by the behaviour of occupants, such as breathing, cooking and bathing – all emitting moisture. However, the designer can influence these effects by specifying suitable controls (such as mechanical ventilators) and reducing thermal bridging to enable the occupant to limit the incidence of surface condensation.

This Wood Information Sheet (WIS) explains the difference between surface and interstitial condensation and describes design measures to reduce the incidence of condensation.

Contents:
Surface condensation
Interstitial condensation
Factors that affect condensation
Control of condensation
Design measures to reduce condensation
Properties, units and definitions related to water vapour in air and in materials

Key Information

The dew point is the temperature below which the water vapour in the air will condense into liquid water.

Sensible design and detailing with good supervision of construction can reduce or eliminate these risks. Factors such as building use, occupancy levels, temperature and the type of heating/ventilation system all need to be considered.

Ensure that vapour transmission into the structure is controlled and that vapour can escape to the outside.

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