I regularly have a problem with mould in my flat. It appears on the frames of windows or above the windows. I clean it when it appears but I would like it not to appear at all. What can I do besides opening the window more often (which I don't want to because it's too cold)?

4 Answers 4


The answer from @nielsnielsen is a good start. I would add that in some extreme cases, a de-humidifier might also help. Read about the topic on the net.

However, the air humidity itself is not the biggest issue. The biggest issue is that the humidity in the air (the vapors) condensate on cold surfaces, and that condensated water is the ideal environment for the mold to grow.

Especially taking into account that the mold is on / near the windows, the problem tends to be quite obvious. Either you need some adjustments to your windows, or you need new windows entirely.

Why? Because the low temperature from the outside penetrates "completely" into the room, allowing the vapors to condensate. Either:

  • the surfaces of the windows do not match properly, and air can travel freely between them,
  • or the lifetime of the windows reached an end and they need to be replaced.

Either way, a specialist should be consulted, for the best advice on the topic of windows.

One extra note: make sure that the air can circulate freely in the affected areas. In this way, the condensated water has a chance to evaporate again, before mold will appear. Try any (all) of the following:

  • remove any furniture which is too close to / around / above the windows;
  • remove any curtains / drapes / anything which separates the room from the windows;
  • remove live plants from near / around / in front of the window.

One extra help in thermal insulating your apartment is to add external window blinds. They will create an extra layer of air (insulation), which will keep the cold outside. Of course, they will have to stay open during the day, but the biggest trouble is during the night, when the temperatures are lower.

Other hints (brainstorming, you need to decide depending on your exact details):

  • do not dry clothes in the affected rooms;
  • do not have too many plants; they evaporate the water that they not need;
  • install a kitchen hood; make sure that the vapors go outside, instead of being recirculated inside;
  • install proper air exhausts (ventilators) in the bathrooms; the air with vapors must be moved outside, instead of pushed inside the rest of the apartment;
  • refresh the air inside the apartment more when it is dry outside;
  • refresh the air inside the apartment less when it is wet (rainy) outside;

Mold requires lots of humidity in the air to grow. The quickest way to decrease mold growth in a house is to decrease the humidity inside the house.

This usually is done by 1) circulating the air in the room with a fan and 2) pulling excess moisture out of the air with a dehumidifier.

If you are in a climate where it gets cold in the winter, you can also accomplish this by turning the heat up slightly in the room while allowing fresh outside air to enter the room and stale inside air to leave it. Cold outside air contains little moisture, and heating that air greatly decreases its "effective humidity" (a.k.a. relative humidity) which will dry out the inside of the room. This will slow down mold growth.

  • I already referenced your answer in mine - because you have a good point. However, it is not the vapors in the air which allow the mold to grow, but the environment created by the water being condensated on colder surfaces - the windows in this case, and around them.
    – virolino
    Dec 18, 2019 at 6:18

This isn't a hack but you do need to ventilate rooms, to reduce the water that mould needs to grow, even if you think you are "throwing money away" by letting heat out.

One source of moisture (apart from breathing) is from cooking pots – always use lids on pots and pans to reduce it.

Another is from drying clothes indoors.

Another is from gas cookers, free-standing gas heaters, and paraffin heaters, all of which produce large amounts of water vapour. My understanding is that 1 litre of paraffin produces 1.25 litres of water when burned.


Similarly to you, I know someone that got fed up with mold. Their situation was a bay window in the kitchen that moisture would collect and mold would grow. Their hack was a small fan that would cycle on and off which created the required air movement to keep it dry and thus prevent mold.

  • How was the air from the ventilator moving? What was it directed at? Maybe you should add a few details to the answer, to make it more clear, and therefore more useful.
    – virolino
    Dec 20, 2019 at 6:27

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