Mould growth in living spaces is an annoying, unsightly and, moreover, health-endangering nuisance. Mould spores are present everywhere in the air. On a suitable breeding ground, they settle and multiply. There, very unsightly black, blue or green coatings then form, which are almost impossible to remove. Most people know that mould develops wherever there is sufficient moisture and the temperature permits mould growth. What many people do not know, but which is important for preventing and, if necessary, combating mould: far more moisture is needed for mould to establish itself than for the growth and maintenance of an existing mould colony. "Nip it in the bud" is therefore even more important when preventing mould than with many other types of structural damage, because removing an existing mould infestation is considerably more difficult than avoiding a mould infestation from the outset.
What can I do to prevent mould infestation
To give mould growth no chance, it is necessary to reduce or avoid moisture on walls, ceilings or windows. Moisture can increasingly settle there because, with insufficient ventilation, the indoor air becomes more and more saturated with moisture. The humidity in a room rises slowly through the occupants' breath alone. Added to this is the moisture released during cooking, washing, personal hygiene, drying laundry or by houseplants. If this moisture is not removed regularly through suitable ventilation, it will eventually settle. This always happens wherever surfaces have a lower temperature than the surrounding areas. These can be windows, window frames, external walls or sections of wall that are poorly insulated and act as a thermal bridge. You know the effect from a cold glass of a drink or a pipe carrying cold water, on the outside of which water condenses when the humidity is correspondingly high.
Ventilation strategies to combat mould growth
In principle, sufficient ventilation to reduce the humidity in the indoor air is the right way to prevent mould growth. There are a few rules to observe here. You should know that warm air can absorb more moisture than cold air. This means that ventilation is more effective when the outdoor temperatures are lower, i.e. in the morning or evening. Burst ventilation with windows opened wide provides a considerably better air exchange than continuous ventilation with a tilted window, especially if you simultaneously open windows on opposite façades and create a draught through open doors (cross ventilation). The exception here is bedrooms: anyone who does not want to sleep with the window fully open should at least tilt a window in order to draw off the continuously produced moisture.
It is also important to draw the moisture from special sources outside promptly, such as when cooking, showering or drying laundry. Drying laundry should be avoided as far as possible in living spaces. Hang the laundry outside or use available drying lofts or rooms. Where possible, tumble dryers should have an exhaust connection to the outside in order to carry away the moist air.
Heating correctly helps to prevent mould growth
Since warm air can absorb more moisture than cold air, heating also helps against mould growth. Permanently occupied rooms should therefore be heated to about 20 degrees. It is very unfavourable to "co-heat" cold rooms such as bedrooms by opening the door. Since the walls in these rooms are cold and the inflowing warm air carries a lot of moisture within it, condensation forms on the cold building components and mould growth is inevitable. It is better to keep the doors closed and to heat the room moderately using its own heat source.
Even during periods of absence, the heating should not be switched off completely. With cold walls, reheating takes so long that condensation can form there when the indoor air is warmed up, which can again lead to mould growth.
Structural conditions and mould growth
When building masonry houses, a great deal of moisture is introduced into a building through mortar and plaster. With timber constructions this is not the case to the same extent, but it can also be possible there through plasterboard work, paint or decorative plaster. A sufficiently long drying phase, possibly supported by construction dryers or by running the already installed heating even though no one has yet moved in, ensures a healthy and mould-free indoor climate in a new build or renovated older building.
Poorly insulated building components are colder in relation to other parts of a building, so that moisture condenses there. This can be the entire external wall, a concrete ceiling that runs through to the outside without insulation, or an old window frame that is no longer completely sealed. These defects can, under certain circumstances, be remedied by subsequent insulation or by replacing the windows. It should be noted here that intervening at just one point can lead to condensation continuing at another, then coldest, building component. In any case, when increasing the airtightness of a building, the ventilation behaviour must be adjusted accordingly. Repeated burst ventilation during the day in no way negates the energy savings achieved through better windows or better wall insulation and, alongside preventing mould infestation, ensures a pleasant indoor climate.
