ᐅ Excessive indoor humidity. 60-70% during winter months.

Good day,

I am new here and hope you can help me (even though I am not currently building myself):

We recently moved into a newly painted apartment on the third floor; the building was constructed just before the turn of the millennium.

I noticed that the windows, especially in the mornings in the bedroom, office, and kitchen, are fogged up on the inside edges and have visible water droplets. The windows are partly older wooden windows and partly skylights with metal frames.

I then bought two thermometers/hygrometers from TFA and placed them in the bedroom and kitchen. The humidity levels were between 60-70%.

I have read up online and gathered a lot of tips. We ventilate at least twice a day, usually more often, by fully opening windows for 5-10 minutes maximum, with heating off during this time. The temperature in all rooms is between 19 and 20°C (66-68°F). Laundry is not dried inside the apartment; after showering and cooking, we also ventilate thoroughly and turn on the extractor fan, as well as when the washing machine is running.

Although we notice that during ventilation, the humidity drops to around 40-45%, it rises again within minutes to at least 53% and then slowly moves toward 56-60%. In the morning, the bedroom is about 63-68%, and the kitchen 61-67% (humidity even goes higher during cooking despite ventilation).

We have moisture-absorbing granules in the kitchen and bedroom, but unfortunately, they haven’t made any improvement.

I did not experience this problem at all in my previous apartment and am currently unsure what to do. I plan to start documenting this in writing and then address it with the landlord, but I wanted to ask here first if anyone has any further tips on what I might try.

Thank you very much.

Best regards,
bpe87

Hello,

since the problem occurs in all rooms, I don’t assume it is a structural issue.

You can only manage it long-term by ventilating. If the humidity rises so quickly, your walls are already quite damp. It will take some time to dry them to an acceptable level. So, ventilate, ventilate, ventilate.

The warmer you make the apartment, the faster it will dry. Increase the temperature to around 23°C (73°F) and ventilate more often. The greater the temperature difference between inside and outside, the quicker the apartment will dry.

As for ventilation, the duration doesn’t matter. You basically only need to exchange all the air in the room once. Ideally, open windows on opposite sides of the room when there is some wind. Then it takes less than a minute to refresh the air.

The air will then saturate with moisture again, and as soon as that happens, you can ventilate again.

Hi,

thanks for your response.

So, there is no issue in the living room. The windows there never fog up or become damp.

As I said, we have only been living here for a short time and have always ventilated as described above. If the walls are already damp now, then it’s probably due to the previous tenant’s improper behavior, right? The landlord apparently also told my girlfriend that, for example, the windows and shower seals showed mold when the previous tenant moved out.

Construction-related causes can definitely be ruled out, for example, due to the newer windows?

Would it make sense to use an electric dehumidifier for a short period?

Thanks and best regards
BPE

Heating and ventilation are all that is necessary.

I am also familiar with and use TFA thermometers together with a climate logger for monitoring humidity.

The rarely used rooms usually stabilize just below 20°C (68°F) with relative humidity around just above 60%, typically 61–62%. In this case, the only effective solution is ventilation and slightly increasing the temperature.

This is likely why the relative humidity in your living room is below 60%, as it is probably 1–2°C (2–4°F) warmer there. The absolute humidity is roughly the same in all rooms; the difference is caused by the temperature.

Try to maintain the rooms between 20 and 21°C (68–70°F), and the relative humidity will drop by the few necessary percentage points.

I also suspect poor ventilation by the previous occupant. Your approach sounds good. Try raising the temperature slightly and monitor the humidity throughout the winter.