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Preventing mould – what measures help?

Picture © ivan_kislitsin /

In the heating season in particular mould can soon become a problem. For mould to grow, it needs moisture and in the winter months in particular, not enough moisture is removed from the home to the outdoors. The occupants themselves produce a lot of moisture (e.g. through sweating, showering, bathing, drying laundry and breathing) –– up to twelve litres a day in total. But temperature and the presence of a nutrient base also contribute to the growth of mould. So what can we do to nip this process in the bud?

Infographic: Moisture released in a 4-person household

Preventing mould: Know the cause and act early

If you want to stop mould before it spreads, you first need to find out how it develops in the first place. As shown above, three factors are crucial: moisture, temperature and nutrients.

It's not even necessary for condensation to form. As little as 80 percent humidity on a surface or 65 percent in a room is enough for mould spores to colonise. The moist air condenses in cold places in rooms (known as thermal bridges). But it also happens quickly in areas such as window casements or balconies. Particularly tricky are all those places in houses where hardly any air circulates, such as behind cupboards, curtains or even under floor coverings.

In addition to humidity, mould feels particularly at home at temperatures between 15 and 30 degrees. The surface is not a particularly important factor. Concrete, cement, wood, plasterboard and wallpaper can be breeding grounds just as much as paint or plastic.

Simple tips for preventing mould

It's important to bear in mind that normal air always contains a few mould spores. However, it only presents a risk when the concentration rises above a certain level. Nevertheless, spores should be prevented from settling on an indoor surface and spreading. This can only be achieved through proper ventilation and heating.

Ventilation in particular is often overlooked during winter. This is because many people fear that this will result in too much heat escaping and being wasted. However, it is more a matter of opening the windows fully for five to ten minutes on a regular basis. Ideally, opposite windows and the interior doors should be opened so that a complete exchange of air can take place. To keep heat loss as low as possible, turn down the  radiators  during this time.

Tilt ventilation, on the other hand, often has the opposite effect. Heat is lost unnecessarily and the rooms cool down considerably during the day. Not only does this mean that more energy is needed to warm up the rooms again, it also results in too large a temperature difference between the cooled surfaces and the heating air. In such cases, mouldy areas often form around the windows.

But proper heating should not be neglected either. This is because warm air absorbs more water molecules than cold air. The decisive factor here is which rooms are involved and how long people spend in them. In living rooms, an average temperature of 20 to 22 degrees Celsius is recommended. In other rooms, you can get away with it being a little cooler.

Preventing mould with mechanical ventilation systems

In older buildings, air exchange occurred naturally via leaks, e.g. in wooden windows. However, this is increasingly changing. This is because every renovation measure ensures that as little heating energy as possible is lost through leaky windows, window casements or doors. However, this does not mean that renovations should be abandoned, but rather that ventilation should be adapted to the new conditions. Impact ventilation should be carried out more frequently during the day to transport moisture to the outdoors. New builds are also becoming increasingly more airtight. Ventilation is particularly important here. But in many cases this cannot be done manually, because during the day the occupants are at work, at university or at school. Controlled mechanical ventilation offers a suitable solution for this.

How do ventilation systems prevent mould growth?

Controlled mechanical ventilation provides a consistently healthy indoor climate and sufficient fresh air without losing heat. With integrated heat recovery, it's even possible to recover heat from the extract air and use it for heating. Mechanical air change also ensures that moisture is transported from inside the home to the outdoors. Another form of protection are the filters in the ventilation systems which prevent dirt and particles from entering the interior with the outdoor air.

In this way, both decentralised ventilation systems and centralised mechanical ventilation systems protect against mould growth not only by limiting the symptoms or effects of such an infestation, but also by preventing the causes.

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