Building Surveyor Blog

The greatest cause of dampness in the modern home is condensation.  Condensation occurs when moist air comes in contact with a cold surface e.g. a single glazed window or an uninsulated solid wall.  When warm air, which can hold more water vapour than cold air, comes in contact with such a cold surface it gives up some of its moisture as condensation on that surface.

Take the attached example, a north-facing bedroom in a pre-war cottage where a living room was converted to a bedroom.  The dampness here is caused due to a lack of permanent ventilation to the bedroom and an uninsulated solid concrete wall.

There are a number of gradual steps this house owner can take to eliminate the problem:

1. Lack of ventilation:  The room has a boarded over fireplace and this fireplace could be vented to the outside to include cleaning the flue, providing a vent at original fireplace level and capping off the chimneypot to prevent rain penetration but still maintaining a through flow of air to the flue.  This is the cheapest method of reducing condensation in this case.
2. If option 1 does not work or only partially works the owner will then need to consider improving the insulation of the wall.  This can be done by drylining the wall internally.  It is slightly more disruptive as a radiator will have to be repositioned and all skirting boards, window cill boards and ceiling covings need to be reformed.

Where does the mould come from?

Mould appears as spots or small patches, which may spread to form a furry layer, dark in colour.  The three conditions necessary for mould to grow are:

1. A source of infection - The spurs are freely available in the air and can be found in any building.
2. A source of nourishment - Dust and grease provide the nourishment required and the amount needed is very small and as a result all surfaces will sustain growth.
3. A damp environment - Relative humidity greater than 70% will result in widespread growth.

Cleaning the wall

The wall must be washed down with a suitable fungicidal wash to remove the mould prior to redecoration.  This is merely a cosmetic approach and will not provide a cure until the overall problems of ventilation, insulation and in some cases improved heating are addressed.