One of the many reasons for damp in any property is condensation and this usually leads to mould growth. The presence of moisture and condensation in the various walls inside the building and also on the ceilings helps the mould grow.
In most of the places of the UK, the living condition of many has been affected by condensation. This is also accompanied by the growth of mould. This is one of the largest complaints which have been received by the various authorities of the UK.
A series of comparatively simple conditions give rise to the problem of condensation, mostly in the dwelling houses and this is directly associated to standards and methods of heating, ventilating and insulated buildings.
The air which cannot hold any more water vapour is known as saturated air, this also depends on the existing temperature. The air is said to contain a relative humidity (RH) of 100%. Dew point is the temperature at which the air cannot hold any more water and reaches its saturation point. If the temperature falls further the water vapour transforms into liquid water.
When the warm air comes in contact with the cold surface, condensation in a building takes place. After the air is cooled below the saturation point, the excess water vapour turns into liquid. You can see the vapours in the form of droplets on non-absorbent surfaces such as tiles or windows. This is known as surface condensation.
The fabric of the building can get affected by condensation due to the internal air passing through the structure. The total pressure of the air is enhanced with the water vapour and the pressure exerted by it.
The more moisture present in the air the greater the contribution of water vapour to the total pressure of the air referred to as vapour pressure. Air inside a heated building usually contains more moisture than does the external air.
This means it is at a higher pressure which tends to force the warm air through the structure taking the moisture with it. Most building materials, except metals, plastics and certain lined elements, are to some extent absorbent and do not obstruct the movement of moist air through the structure. The warm moist air will eventually cool below its dew point within the fabric of the building resulting in condensation. This form of condensation is interstitial Condensation.
Interstitial Condensation is rather more complex than the surface condensation and presents a greater hazard because the resulting high moisture content can often go undetected for long periods until serious structural damage has developed such as timber decay.