Every home has mould spores present, most of the time they are dormant and completely harmless. Mould spores exist in all environments indoors and out and at all times of the year. They are part of our natural environment. Mould needs three things in order to exist – moisture, oxygen and something to eat. Mould needs very little nutrient and will grow on wood, plaster, window sills, walls, ceilings.
To eliminate mould growth we need to remove one of the three things mould needs to exist. The food source, we cannot remove as it’s in most building materials we use to build our homes. Oxygen, we can’t remove that, there no point in killing ourselves. This leaves us with only one choice, removing the moisture. We cannot remove all moisture within our homes, but we can control it and limit its adverse effects.
Moisture within our homes comes from two distinct sources, faults within the building structure that let moisture into the dwelling and the moisture we produce while living in the dwelling. Leaking roofs, leaking water pipes, rising damp etc. will increase the moisture levels in the home. These sources are relativity easily to correct. Other sources of moisture within our homes come from a variety of different occupational activities, like cooking, showering, drying clothes. The list goes on. All these activities add moisture to our indoor environment and the problem arises when condensation forms on surfaces.
The formation of condensation occurs when the moisture vapour in the air touches a cooler surface that is below the dew point of the moisture vapour. The dew point is not a single temperature point, but a relationship between the air temperature and the relative humidity of the air. As the relative humidity rises for a given temperature the dew point also rises. To give an example, let's assume an indoor temperature of 20 degrees. When the relative humidity reaches 70%, the dew point will be at 14 degrees. This means that the moisture in the air will condense onto surfaces with a temperature of 14 degrees or below. In these conditions mould growth will occur within 24 weeks. If the relative humidity rises 75% the surface temperature will need to be above 15 degrees or mould growth will occur in 6 weeks and at 80% the surfaces will need to be above 16 degrees or mould growth will occur within 2 weeks. To experiment with dew points www.dpcalc.org has a dew point calculator you can try out.
Air moves naturally around our homes and in doing so carries the moisture with it. The temperature within each room of our home is not always the same so we may find that some rooms are colder than others; we may have a bedroom in an external corner of our house or we may have turned off a radiator in an unused room. The temperature of surfaces within a particular room may also vary according to its location. Cooler surfaces may be found, for instance, behind large pieces of furniture against an outside wall e.g. wardrobes or the wall below a window or a bedroom ceiling against an outside wall.
As the moist air moves around our home it will come into contact with all these surfaces. If we use the example above where the relative humidity is 70% we will find that condensation will occur on all surfaces with a temperature of 14 degrees or below. This is where, given time, mould is likely to grow.
Controllable ventilation is provided as standard within our homes and the need to ventilate has been explained. By controlling the moisture within are homes we can eliminate mould. We don’t have to leave the windows open all the time to get rid of the moisture. Remember it takes time for mould to grow and it needs moisture or it will die. If you want to keep all the windows closed during a cold February day or even a week then do so, but when the weather conditions improve, open the windows and let air in and the moisture out. Let the surfaces dry out. Once dry the spores will be unable to grow.