Condensation can reveal itself in a number of ways; the most common are the presence of condensate, mould growth, decay of timber and corrosion of metals.
Condensation is caused when the amount of moisture in the air increases to such an extent that the air is no longer about to transport the moisture as vapour. When this occurs the air is deemed to be saturated or at 100% relative humidity (Rh), when this moist air is allowed to come into contact with cold surfaces, condensate can form, the temperature of the surface that allows this to occur is called "Dew Point"
The % of Rh is directly linked to the temperature of the air, the colder the air the higher the Rh, as air warms the Rh reduces.
Condensate on surfaces
Condensate frequently occurs on:
- single glazing in bedrooms overnight or in kitchens and bathrooms at any time;
- double glazing, especially near the frames, in rooms with relatively high humidities;
- on WC cisterns or cold pipes in bathrooms or kitchens;
- on the walls of hallways and stairs in buildings of heavy masonry construction after a change from cold dry weather to mild wet weather;
- on the underside of lightweight single-skin roofs of industrial buildings due to night sky radiation;
- on massive floors in offices or industrial buildings, which remain cold after a change to warmer more humid weather, or when heating is turned on in the morning;
- on the walls or surrounds of swimming pools.
Condensate is often only a nuisance but more serious consequences can result from, for example:
- condensate from glazing promoting decay in wooden window frames or condensate running from sills onto the wall below, damaging decor;
- condensate dripping from roofs onto food preparation processes or sensitive electronic equipment;
- condensate on certain floor types making them slippery.
Sometimes, condensation can be dealt with by drainage or by mopping it up before it collects and runs to vulnerable areas. Persistent severe condensation on glazing, especially double glazing, in many rooms suggests that excessive moisture is being produced or ventilation within the dwelling is inadequate; these can lead to more serious problems.
Mould growth is often associated with surface condensation; damp houses can provide good conditions for its development.
Mould spores exist in large numbers in the atmosphere; to germinate, they need a nutrient, oxygen, a suitable temperature and moisture. Sources of nutrition are widespread in buildings and the internal environment provides a suitable temperature for growth. Oxygen is always present so mould growth is particularly dependent on moisture conditions at surfaces and the length of time these conditions exist. Moulds do not need water but can germinate and grow if the relative humidity at a surface rises above 80%. This is considerably less severe than the 100% required for surface condensation to occur. As the internal surfaces of external walls are colder than the air temperature within the building in winter, the relative humidity at the wall will be about 10% higher than in the centre of a room. This temperature and relative humidity difference will be reduced if the walls are well insulated. But as a guide, it can be assumed that the relative humidity at the external wall surfaces will be high enough to support the growth of moulds if the average relative humidity within a room stays at 70% for a long period of time.
Moulds and mildews can occur on furniture, curtains, carpets and clothing, especially leather jackets, shoes or suitcases, if they are in unheated spaces or in parts of rooms sheltered from heating systems. Unheated bedrooms, cupboards or wardrobes placed against external walls and items stored in roof spaces are especially vulnerable.
There are three key factors that can lead to condensation
- insufficient ventilation
- insufficient heat
- excessive moisture creation (drying clothes on radiators, leaving wet room doors open during bathing or cooking, over occupation, using portable gas heaters).
To alleviate the creation of condensate these three factors need to be addressed, by providing adequate ventilation based on the occupancy and lifestyle of the occupants.
To increase the heating to all rooms of the property to greater than 17degress ( this can be problematic when the occupants are in fuel poverty).
Reduce the moisture creation by addressing the issues above.
To ensure a healthy indoor environment for the occupants it is important to ensure that the building is in moisture balance.