In many houses, especially older ones, excessive humidity in the basement is a serious problem. If there is a musty smell in the basement, the plaster is peeling off the basement walls or mold is forming, you should act immediately. Excessive humidity endangers the building fabric of your home and the health of everyone who lives there. Read our article “Mold: prevention is better than removal or remediation”.
The older the house, the more likely it is to have damp in the basement. Until the 1950s, the parts of houses in contact with the ground were hardly sealed at all, so damp walls in the basement are inherent to the construction. After that, the basement walls were sealed and the first floor slabs were laid, but still without protective films. It was not until the 1970s that houses were built with waterproof concrete basements or the basements were lined with waterproof material. Nevertheless, basements in old buildings from 1970 onwards or new-build basements are not safe from damp. On the one hand, all waterproofing materials become brittle and cracked with age, on the other hand, water can penetrate through a burst pipe or powerful tree roots can damage the masonry. Recently, there has been an increase in damage caused by groundwater penetrating through the basement walls because heavy summer rainfall overloads the sewer system.
In living spaces, 40 to 60 percent relative humidity is ideal. The ideal humidity in the basement depends on how you use the basement: If you use the basement ...
During the day in summer, the air outside is warmer and more humid than in the basement. You should therefore not ventilate or only ventilate at night or in the early morning, or better still cross-ventilate when the outside temperature is a few degrees below the basement temperature and the outside air is less humid. You can close the window(s) again after 20 minutes. Airing during the day is a mistake in summer: the warm and humid outside air cools down quickly, the moisture condenses and forms condensation on the basement walls. This is the basis for mold growth in the basement.
In our article “Proper Ventilation in Winter Improves the Climate and Prevents Mold” you will find many tips on how you can easily protect the health of your family and the building fabric of your home.
In winter, the air outside is colder than in the basement. If you want to reduce the humidity or keep it low, ventilate the basement for 10 to 15 minutes a day at most, preferably on cold and dry winter days. The cold outside air warms up, absorbs humidity, draws moisture from the masonry and thus slowly dries out the basement. As long as the outside temperature is not far below 0 degrees, you can also ventilate during the day, for example while the laundry is drying. However, make sure that the cellar does not cool down too much. Especially if you use it as a living space.
If you store food in the cellar, the room temperature must not fall below 0 degrees.
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Warm air absorbs more moisture than cold air. That is why it is sometimes enough to increase the cellar temperature by 1 or 2 degrees in winter to reduce the humidity. However, keep a close eye on heating costs: this type of humidity control can become expensive over time.
A dehumidifier is useful if ventilation alone is not enough and/or you do not want to ventilate every day. Good condensation dehumidifiers for cellars are available from any DIY store or specialist retailer from CHF 200, are easy to operate and quiet. When choosing an appliance, pay attention to the area of the cellar, the capacity, the size of the water tank, the power consumption and the noise level. It is important that the dehumidifier switches on automatically as soon as the humidity rises above the target value and switches off as soon as it falls below it. The larger the tank, the less often you need to empty it.
It is better to buy an energy-efficient dehumidifier, which costs a little more but uses less electricity and is therefore cheaper than a cheap dehumidifier.
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Automatic cellar ventilation is even more convenient than a dehumidifier. Thanks to regular air exchange, it ensures a consistently better indoor climate, prevents musty odors and prevents moisture damage such as mold. Sensors continuously measure the humidity and temperature of the indoor and outdoor air. As soon as the humidity in the cellar rises above a certain level, the fan switches on automatically and runs until the humidity has fallen below the desired level (see “Ideal humidity in the cellar”).
Automatic ventilation is useful if you have moisture problems in your cellar, use your cellar as additional living space or want to store wine in a climate-controlled environment, for example. Installation is also possible at a later date without any problems. As a rule, all you need is a power connection for the fan and the control technology. The fan can be installed in a window or ventilation shaft. If not, a simple wall opening of plus/minus 20 centimeters in diameter is sufficient. Cellar ventilation systems are available with or without heat recovery. With heat recovery, the ventilation systems are particularly energy-efficient because they reduce energy consumption by around 90 percent.
