Faq preventing mold how to avoid mold in your rooms

The experts at Stiftung Warentest answer the most important questions about mold prevention, rooms at particular risk and helpful construction measures.

Bundled information against mold

More tips and information on the subject of mold can be found in our mold removal FAQ. Good sprays that effectively combat fungal spores can be found in the mold remover test. Which rights and obligations tenants have with mold infestation, you read in our special mold in the dwelling – these rights have tenants.

Book tips: Tips for renovating, building and repairing can be found in our book Supertricks fur Heimwerker. Helpful is also our guide repairs at home – renovation, restoration, repair. It contains many illustrated instructions, including how to get rid of mold stains.

  • Why mold develops?
  • When is the risk of mold at its highest?
  • Why does mold grow in some places and not in others??
  • How dangerous to health is mold??
  • Favors too little heating mold?
  • How can I determine whether it is too damp in a room??
  • What are indications of mold?
  • How to ventilate properly?
  • I air at least three times a day in the push. Nevertheless it molds. Why?
  • Where mold forms particularly often?
  • My plant soil keeps getting moldy. Since I have problems with mold in the apartment as a whole, I wonder if this has something to do with each other.
  • How do I find mold endangered places?
  • I want to heat my bedroom as little as possible, although test advises to do so. How can I reduce the risk of mold anyway??
  • How to prevent mold in the bathroom?
  • How do I prevent mold in a fen-less bathroom without electrical ventilation??
  • Do built-in fans with hygroscopic control replace ventilation in the bathroom??
  • It is normal that it is damp in the cellar. So there is no danger of mold?
  • What can I do to prevent mold from forming in basement apartments and cellars??
  • How to protect my house exterior from dampness and mold?
  • What to do if there is still water damage?
  • Does thermal insulation increase the risk of mold??
  • What do you think about interior insulation?
  • I am building my own home. How can I plan it as mold resistant as possible?
  • What do you think about windows with forced ventilation?? On the one hand, a minimal air exchange is guaranteed, on the other hand, the rooms cool down as a result.
  • In former times it was said that new houses must be "dry-lived". What is involved?
  • What is the benefit of a dehumidifier?

How mold develops

Why mold develops?

Mold growth is always a result of too much humidity. From broken roof tiles to defective rain gutters and leaking pipes to rising ground water, many things are possible. A common cause are so-called thermal breaks, such as cantilevered concrete and steel parts to the balcony or at window lintels without insulation. But poorly insulated exterior walls, which get so cold on the room side in winter that air moisture condenses there, can also promote mold. Moisture fodder is also provided by normal life in the home: normal sweating, showering, cooking and drying clothes add up to several liters of water per day. If this moisture is not transported out of the apartment by regular ventilation, it can condense on cold walls – similar to a bottle that you take out of the refrigerator on a sultry summer day.

When is the risk of mold at its highest?

Mold spores are always and everywhere present in the air. In order to grow and multiply en masse, however, they need one thing above all: moisture. In winter, the fungi often find these ideal living conditions on cold walls. If exterior walls cool down too much, problems can arise even in well-ventilated apartments: Water condenses in the coldest places.

Tip. You suspect building defects as the cause of mold infestation in your home? What rights you have as a tenant and how you can best enforce them, read in our special mold in the apartment – These rights have tenants.

Why does mold grow in some places and not in others??

With regard to the substrate, many species of mold are quite sufficient. Often they settle for example on wallpaper or even on plaster. The basic prerequisite for any mold infestation is, however, in any case an increased level of humidity. Where this moisture comes from can vary greatly: one common cause is poorly insulated exterior walls that get so cold on the room side in winter that air moisture condenses there. About how to get on the track of mold and how you can eliminate the causes, also inform our three free info documents:

How healthy-dangerous is mold??

In general, mold spores can irritate mucous membranes and lead to respiratory diseases. The typical musty mold smell also contains mycotoxins. These are toxins produced by the fungi, which can damage the body and in extreme cases even cause cancer. Particularly at risk are people who are allergic to molds or people with weakened immune systems. Where molds attack walls and materials, certain types of bacteria (actinomycetes) often spread as well. Although the health effects of actinomycetes cannot yet be assessed, initial studies have shown, according to the Federal Environment Agency, that the bacteria can be harmful to living cells in cell cultures.

How to give mold no chance in everyday life

Does too little heating promote mold??

Airing without heating is like city traffic without bus and train: the transport capacity would not be sufficient. In order to transport a lot of moisture out of the apartment, the air must be sufficiently warm. Because warm air can absorb much more water than cold air. Recommended are temperatures around 20 degrees Celsius, in the bathroom and living room a little more and in the bedroom a little less. But nowhere below 16 degrees. Therefore, do not let any room cool down too much. Especially the bathroom should always be heated.

Tip: Your landlord blames you for the mold? Read in our Special mold in the dwelling – these rights have tenants, which rights, in addition, obligations tenants have.

How can I determine whether it is too damp in a room??

Exact measurement values are provided by an air humidity meter. Hygro-meters with digital display are more reliable and convenient than those with manual display, because they do not need to be calibrated. The purchase of such a measuring device for about 20 euros is highly recommended for households with humidity and mold problems or those that operate water evaporators. Comparative measurements are good: on one side in the center of the room and on the other side at the coldest point of an outside wall.

Tip. Check if your hygro-meter measures correctly. Wrap it in a damp cloth for an hour for this purpose. It should then show about 95 percent humidity. If not, there is sometimes the chance to readjust on the back side. Alternative: Set up the device outside in dry, warm and stable weather and compare the display with the data from the local weather station.

What are indications of mold?

Suspicions are musty smell, water stains and – in winter – damp window frames and heavily fogged glasses when entering the apartment. Also dust lice are an indication of mold. The insects, which are about two millimeters in size, feed on mold. Dust lice very rarely cause allergies. However, those affected by mold should not expect dust bunnies to "eat away" the mold problem. If you want to get rid of dust bunnies, you should avoid insecticides. They only help for a short time. First and foremost, get rid of mold. The dust bunnies disappear with it.

Tip. You can find tips for the removal of mold in our FAQ Removing mold.

How to ventilate properly?

Shock ventilation is the most efficient method, i.e. it is best to open windows wide for five to ten minutes and ventilate the entire apartment. You should air the apartment at least twice a day in this way. Better even three times: in the morning, before you leave the house; in the afternoon or evening, when you come home from work; and once again, just before you go to bed. In addition, it can be useful to ventilate the bathroom or kitchen after showering or cooking, so that the vapor can escape. The colder it is outside, the more effective ventilation is, because dry cold air can absorb a lot of water.

I air at least three times a day in the bump. Nevertheless it molds. Why?

Often mold problems are not due solely to incorrect heating and ventilation behavior, but are related to structural defects. Cold outside walls are often a consequence of missing or insufficient facade insulation. Walls cool down particularly easily at so-called thermal breaks, such as cantilevered concrete and steel parts facing the balcony or window lintels without insulation. Moisture tends to collect here. Sometimes the structural deficiencies are so serious that simple heating and ventilation are no longer sufficient. If water constantly penetrates through a leaky roof, cracks in the outer facade or a blocked rain gutter, even the best heating system cannot dry the wall in winter. In basements, groundwater or seepage can become a problem if the walls or floor are not properly sealed. Also splash water in the base range of the house can lead to dampness damage in the wall. Then mold can hardly be avoided by the inhabitants.

Tip. You suspect structural cause for the mold infestation in your apartment? What you can do you read in our special mold in the apartment – These rights have tenants.

Where mold is particularly common – and what to do about it

Where mold forms particularly often?

Molds prefer to colonize bathrooms. 53 percent of those affected in a non-representative survey on test.de from 2013 have discovered mold stains there. In second place on the popularity scale are bedrooms (40 percent of apartments with mold problems). One reason: bedrooms are the coolest rooms in many apartments. It is difficult here to ventilate away the moisture sweated out during sleep. Kitchens, children’s rooms and living rooms are also frequently affected. Particularly problematic in living rooms are poorly ventilated areas behind curtains, beds and cupboards that are too close to the wall. Also critical: wall cupboards, storerooms, blinds boxes. The participants in the survey also had the opportunity to name other affected rooms. This is especially the case in living areas with little or no heating, such as porches, staircases, hallways, glazed loggias or conservatories.

Molds like it damp and cold – this is shown by the answers to the question about infested areas. 59 percent of those affected cite cold exterior walls. The reason: Here the air humidity condenses. Micro-organisms also like to colonize the cool window and door frames (for example on the silicone seal of the glazing) or the reveal area. In each case about 30 per cent have discovered stains here. Further often called problem zones: Tile joints or silicone seals in the sanitary area (29 percent), cool ceilings (13 percent) and the area behind cabinets, wall coverings and pictures (16 percent). Also here the insufficient thermal insulation of the external facade makes itself often negatively noticeable. Other frequently mentioned problem areas are roller shutter boxes, radiator niches, corners of rooms, shower cubicles and mattresses.

Tip: Particularly often mold develops in tile joints in bathrooms. How you can fight the infestation, you can read in our FAQ mold eliminate.

My plant soil keeps getting moldy. Since I have problems with mold in the apartment, I wonder if it has something to do with each other.

Moldy plant soil can be a stove for increased spore contamination of the indoor air. The best way is to change the water once a year and not to water the plants too often. The soil must be allowed to dry on the surface in the meantime. Possibly reduce the number of plants.

How to find mold-prone areas?

Where house walls get very cold inside, moisture is most likely to condense. Critical areas can often be felt with the bare hand. Check there specifically with a thermo-meter. For comparison, also measure the surface temperature of other room walls that are not exterior walls, as well as the air temperatures outside and inside. Infrared thermometers enable fast, contact-free measurements. Aim at the target, press the button and read the temperature on the display. Pen or pistol-shaped models are available for considerably less than 100 euros. In the case of the more expensive products, a red light beam helps to identify the target. With approximately 200 euro it becomes still more expensive, if you schi-cken an energy consultant with infrared camera on the Pirsch.

I would like to heat my bedroom as little as possible, although test advises me to do so. How can I reduce the risk of mold anyway??

Do not turn off the heating completely, at least during the day. If the temperature in the bedroom is lower than in the rest of the apartment, the connecting door must not be left open all the time. Ventilate the bedroom as often as the rest of the house.

How to prevent mold in the bathroom?

Bathrooms are particularly at risk. Both because of the water that directly wets the tiles, and because of the water that evaporates here in various places and then condenses on cool surfaces. In some cases, closed shower cubicle doors exacerbate the problem: moisture is virtually trapped inside the cubicle. This helps the molds to ideal growth conditions. So it is better to leave the door open. It is also useful to wipe the wet tiles with a rubber lip after showering. This is a device used by professional window cleaners. This allows the water to be optimally conveyed in the direction of the drain. Where water splashes, it makes sense to seal the surfaces well, for example with tiles. Otherwise, in bathrooms it can be useful to have surfaces made of, for example, plasterboard with normal diffusion-open paint, which can serve as a sort of buffer for air humidity. Such buffers release their moisture again during subsequent shock ventilation. Proper heating is also very important. Bathrooms should be the warmest rooms in apartments.

Tip: Mold in tile joints of bathrooms is often particularly stubborn. How to help against it, you can read in our FAQ Eliminate mold.

How to prevent mold in a fens-less bathroom without electric ventilation?

If ventilation is not possible, at least the exhaust shaft should be connected to a ventilator. Help can also a squeegee, with which you can wipe the moisture from the tiles (also available commercially under the name "bathroom wiper"). Most importantly, however, the bath-room should always be as warm as possible. So the air can absorb a lot of moisture, which can then be ventilated away. It is also helpful to leave the bathroom door open most of the time.

Replace built-in fans with hygroscopic control the ventilation in the bathroom?

We have not tested such devices yet, but they are basically useful for eliminating dampness in the bathroom. Principle of these devices is that the fan starts when the air humidity reaches a certain level. If it turns out that the built-in fan is running all the time, this is an indication that the fan is not sufficient and additional measures must be taken.

It is normal that it is humid in the cellar. So there is no danger of mold?

Who ignores the dampness, lives dangerously. Every day with damp walls and damp furnishings increases the risk of mold infestation, warns the Federal Environment Agency. If the mold is in the basement, spores can blow through cracks and staircases into living rooms above. Only the drainage of the basement can contain mold permanently.

Tip. In our info document

What can I do to prevent mold from forming in basement apartments and cellars??

As paradoxical as it sounds: Ventilate less. On sweltering heat days, constantly open basement windows can do more harm than good. With the fresh air also much dampness penetrates into the house. When this air cools down on the cold cellar walls, water condenses on wall surfaces, floors and pipes – similar to a beverage bottle from a refrigerator. If you want to prevent moisture and mold problems on hot summer days, you should not ventilate at all during the day, but only at night or in the early morning. During these times the outside temperature is closer to the basement temperature. Also avoid drying laundry in the basement.

How to protect the outside of my house from moisture and mold??

Check. Clean rain gutters, downpipes and floor drains at least once a year after leaves fall. During the next heavy rainfall, check around the house whether the water can run off unhindered and whether gutters and pipes are tight. Small leaks can also be sealed temporarily with special bitumen adhesive tape (available from DIY stores and roofing dealers).

Roof damage. Have defective or slipped tiles repaired in a roundabout way. If the roofer is on site anyway, you should also have him check the valley and flashings (for example on the chimney stone).

What to do if there is still water damage?

Act immediately. Fight water in the house quickly, because over time the damage will be greater. First step: pump out and mop up.

Clean out. Afterwards clear out the room as completely as possible. Remove damp wall coverings and floor coverings, dispose of them or dry them in the attic.

Airing. Hourly shock-ventilation with draught is optimal.

Drying. Radiant heaters and fans are simple tools to combat water damage. Downside: the energy costs. Condensation dryers are more economical: the moisture in the air condenses on a cooled surface and flows into a container. Targeted heating of damp areas can support the process. In order to dry out problem areas such as the fully saturated insulation layer under the screed, it is often necessary to drill and open the edge strips. Then pre-dried air must be pressed or sucked through the damp area. Adsorption dryers, in which granules bind the moisture in the air, are particularly effective in drying. Borrow professional drying equipment for larger water damages.

Compare. Who lends drying devices or assigns companies, should catch up absolutely cost and achievement comparisons (including energy costs). The consumer center Thuringia recommends contracts with running time-independent fixed price agreement.

Expert advice. In case of doubt, always seek the advice of an expert. Especially if the dampness becomes a permanent problem, the causes must be searched for. Consumer advice can help.

After-care. The deeper the water has penetrated materials, the longer drying takes. Increased airing may be necessary for months to come. And even after that, shock ventilation is a must (three to four times a day for about ten minutes)!

Heating. If your basement is always a bit damp-prone, a small amount of waterproofing can be useful. The free surplus heat of a solar system is ideally suited for this purpose.

Independent. Objective. Incorruptible.

Which structural measures really help

Does thermal insulation increase the risk of mold??

This is a myth. In truth, the opposite is true: a survey by test.de shows that an infestation with molds threatens particularly at the inside of cold outside walls. So, where the thermal insulation is poor or non-existent. Who insulates the house, provides for warmer walls, on which the air humidity existing in the rooms can hardly condense. Mold has poor chances here. If fungi infest insulated apartments, this may be due to faulty insulation. Moist air can penetrate through their leaks. Often mold also develops as a result of the installation of new, tighter windows. They need to be opened for ventilation more often than the old leaky ones. If you neglect it, you risk too high humidity in the room. The info document

What do you think about interior insulation?

Who can insulate outside, should not insulate inside. Because interior insulation is considered complicated by experts. They are especially useful in listed buildings with ornate facades. It is important to first make sure that no water is seeping into the wall from the outside or from a damaged pipe.

I am building my own home. How to design it to be as mold-resistant as possible?

Plan. Moisture, such as that caused by showering or cooking, can be removed by automatic ventilation systems. Important: The systems should be equipped with heat recovery to avoid unnecessary energy consumption. Careful building waterproofing and efficient drainage can protect against damp cellars. In case of problematic building ground it is cheaper and more trouble-saving to do without a cellar. In any case, it is advisable to divert rainwater as far away from the house as possible with the help of roof overhangs, canopies and clever garden design – for example, into a garden pond.

Execute. If you are building in winter, you should cover the openings with tarpaulins or install doors and windows early. If the roof is missing, the wall crowns must be protected with a foil, sometimes an emergency roof is necessary. If heating is used on the first floor to dry out the walls, the stairwell must be sealed. Otherwise the air is drawn into the attic, cools down and condenses. Wood and walls will absorb moisture and mold. The contract with the construction company should clearly state what it must do in winter. Builders should have contract and site inspected by experts.

What do you think about windows with forced ventilation?? On the one hand, a minimal exchange of air is guaranteed, on the other hand, the rooms cool down as a result.

Nothing. From an energetic point of view, this corresponds to a constant loss of energy. Who fears for certain reasons that he cannot ventilate frequently enough manually, should think about an automatic ventilation system with heat recovery.

In the past, it was said that new houses must be "dry-living". What is it all about?

Be careful when moving into new buildings or after renovation work. In the building materials much water is, which can escape only in the course of many months. In this period, proper heating and ventilation is particularly important. "Dry-living" is still topical.

What is the benefit of a dehumidifier??

Only who can ventilate little, should buy a dehumidifier. The devices often cost more than 100 euros.

Tip. For tips on how to get rid of mold, see our FAQ Eliminating Mold.

This FAQ was last updated in January 2022. Older user comments refer to older versions.

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