What is Condensation...


Condensation is by far the most common cause of dampness in buildings, probably accounting for the majority of damp problems reported. It affects both old and new buildings but it appears to be a significant problem where the building has been modernised.

Condensation is directly associated with mould growth. It is this that the occupier sees first, and it gives an indication of the potential scale of the problem. The mould is usually found on decorative surfaces, especially wallpapers, where it can cause severe and permanent spoiling. In many cases, the mould and its spores (‘seeds’) give rise to complaints about health, and cause the “musty” odour frequently associated with a damp house.

The obvious places for condensation to occur are on cold walls and floors. It can also occur in roof spaces and in sub-floor areas where there is a timber suspended floor; in the latter case it can lead to rot developing in floor timbers.

It is a fact that warm air can hold more water as vapour than cool air. Condensation is caused when moisture-laden air comes into contact with a cold surface – the air is cooled to the point where it can no longer hold its burden of water vapour. At this point, known as the Dew Point, water begins to drop out of the air, and is seen as condensation on surfaces. On impervious surfaces such as glass and gloss paint, beads, or a film of water collects. On permeable surfaces, such as wallpaper and porous plaster, the condensing water is absorbed into the material. Therefore, the problem is not always initially obvious.

Recognising Condensation-

Condensation is very much a seasonal problem, occurring more during the colder months – October to April. During the summer, the problem often subsides somewhat. During the winter, ventilation of the house is usually low (due to windows and doors being closed, draught-proofing takes place). This allows build up of water vapour in the house, which, in some cases is sufficient to cause condensation.

This condensation becomes apparent from the following symptoms:
Water droplets form on cold, impervious surfaces such as glass and paint.
Slightly damp wallpaper (often not noticed).
Development of moulds, usually black or greyish coloured mould.

In some cases, condensation may be long term, but intermittent, forming only at certain times of the day or night. In these cases, the only sign of condensation may be mould growth, as the moisture may have evaporated by the time moisture measurements are taken.

One should also be aware that the problem can occur well away from the site of most water vapour production. e.g. water vapour produced in the kitchen may diffuse through the house into a cold bedroom where it will condense on cold walls.

Confirmation –
If you wish to confirm that there is a condensation risk, then a Humiditect card can be affixed to the surface where condensation is suspected for 7 days (due to the intermittent nature of the problem). Spots of colour printed on the card will gradually bleed depending on the severity of the problem.

 

 

The Solution –
The control of condensation is based on two very simple primary measures, supported by a number of secondary measures.

Primary Measure –
Improve Ventilation
This will sweep away the internal moisture-laden air and replace it with drier air from the outside (yes, external air is drier than internal air most of the year!)

Ventilation can be achieved by opening a few windows, installing air vents, and using extractor fans. However, it is most effective to remove the water vapour from where it is usually generated, e.g. kitchens and bathrooms. This can be achieved by the installation of a powered extractor fan. Better still, rather than making the occupant responsible for operating the fan, a humidistat controlled unit can be used. These activate when moisture levels in the atmosphere reach a point at which they begin to cause a problem.

Another approach, should condensation be widespread is to use a ‘positive pressure system’. Or the insulation of extractor fans. Please contact us via telephone should you wish to discuss these options.


In most cases, implementing the primary measures described above will effectively control a condensation problem. However, in more severe cases, it may be necessary to implement one or more of the following support measures.

Remove excess water sources
This means removing systems within the house that generate excess water vapour. e.g. bottled gas and paraffin heaters generate enormous amounts of water vapour. These alone may be responsible for the condensation. Further examples of excess water sources include the drying of clothes indoors, or the venting of a clothes drier into the interior of the property.

Insulate Cold Surfaces

Some building materials have better thermal properties than others.
Where solid walls are encountered (or cold, solid floors) these may be insulated by various dry-lining techniques or, in the least expensive case, the use of a thin polystyrene sheet applied directly to the wall. In all cases, this will lead to a warmer surface, thus lowering the risk of condensation. It is also prudent to provide a vapour check on the warm side of the insulation to prevent problems behind and deeper within the wall.

Prevent possible Water Penetration
Damp walls have poorer thermal properties than dry walls and are therefore slightly cooler. And so are more at risk from condensation.
Treating external surfaces with a silicone water-repellent, such as Safeguard Raincheck or Raincheck can help in some cases. This prevents water penetration, thus maintaining better thermal properties of external walls.

Install a dehumidifier
Dehumidifiers remove water from the atmosphere; they lower the water content of the air, and therefore lower the risk of condensation. One strategically placed dehumidifier can be very effective.

Use an anti-mold paint
The most important side-effect of condensation is mould growth and the unhealthy spores that it releases into the air. The quickest way to eliminate mould growth is by the use of a good quality anti-mould paint. However, the long term aim should be to eliminate the condensation that allows the mould to grow.