Warm air can hold more moisture than cold air. If air in a building acquires additional
moisture this increased moisture content will not be apparent in places where
the air is also warmed. But if this
moist air comes into contact with colder air, or with a cold surface, then air
is likely to be cooled to its dew point temperature and sample of air is likely
to be saturated, and the excess water vapour condenses to a liquid.
This effect could also be achieved by the same body of air without the
addition of moisture, being allowed to cool down until it reaches its
saturation point (dew point).
Condensation
in buildings is a form of dampness caused by excess water vapour in the
air. Among the effects of condensation
are misting of windows, beads of water on non-absorbent materials and mould
growth.
As a general principal it can be stated that:
Condensation occurs whenever moisture
laden air meets
surfaces that are at or below the dew point of
that air.
The two types of condensation can be classified into two main types:
1.
Surface
Condensation;
2.
Interstitial
Condensation.
Surface Condensation
Surface
condensation occurs on the surfaces of walls, windows, ceilings and floors. The condensation appears as a film of
moisture or beads of water on a surface and is most obvious on the harder, more
impervious surfaces such as ceramic wall tiles.
An absorbent surface may not show condensation at first, although
persistent condensation will eventually cause dampness.
Interstitial Condensation
Interstitial Condensation occurs within the construction of the
building. Most building materials are, to some extent, permeable to water
vapour (that is, they allow the passage of air containing moisture). If this air cools as it passes through the
structure then, at the dew point temperature, condensation will begin to occur
inside the structure and can damage important structural materials, such as
steelwork.
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