Dampness and mould growth are recognised as major problems affecting a
significant proportion of houses in the North America. Apart from health problems associated with dampness and mould growth, wood decay is also significant problem.
Mould growth in houses is unsightly. But most important, there is considerable evidence to support the view that mouldy housing has a detrimental effect on the health of occupants residing in such environments. This is a cause for concern, considering that many individuals spend most of their time indoors especially during winter. Respiratory problems and allergic reactions are the common health problems associated with mould. Generally, indoor moulds affect people through inhalation of airborne spores. High levels of airborne spores may occur due to growth of mould on walls and furnishings.
Requirements For Mould Growth
Requirements for mould growth in buildings include:
- nutrients: found in the materials which make up or are deposited on indoor surfaces
- oxygen. Like most other living things, common indoor moulds require air (oxygen) for growth.
- suitable temperature (around 25 degrees Celcius)
- moisture: the relative humidity (RH) at a surface is the best indicator of moisture available for mould growth.
In most cases, mould growth in homes is caused by condensation. Condensation in buildings occurs where moist air meets a cold surface. For example if air meets cold water pipes, window glasses or other cold surfaces and is cooled below its dew point temperature, the vapour close to the surface becomes saturated and excess vapour turns to liquid.
There are two types of condensation:
- Surface condensation. Surface condensation occurs at the surface of the material.
- Interstitial condensation. Interstitial condensation occurs inside a material. If vapour passes through porous building materials and the dew point temperature occurs within that material then the vapour will condense. Interstitial condensation is responsible for mould growth in building envelopes.
The major factors influencing condensation in buildings include:
- Moisture production from sources inside the building. Moisture sources include respiration, cooking, washing and drying of clothes.
- Air and structural temperatures
- Ventilation. Proper ventilation helps to reduce condensation.