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
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,
vacant properties are always a problem. Once the walls are damp, it takes time for the moisture to dry out again. This is completely normal. Believing that ventilating twice a day is enough is unfortunately completely wrong. This misconception has persisted for years but is entirely insufficient in houses built in recent decades (after 1990). Even just the airtight windows prevent air exchange. In the past, you could feel drafts everywhere (my oldest house dates back to 1692—when it's windy, all the candles flicker). When drafts occurred, heating was increased, which in turn led to dry air. That’s no longer the case today, and to make matters worse, there is a “saving is cool” mentality. We are saving ourselves sick.
In principle, two windows permanently tilted open opposite each other would be ideal for air exchange. The problem is that the constantly incoming air cools down the areas around the window, and that is the main reason why tilted ventilation is bad. Moisture condenses on the “cold wall,” leading to mold. This is why mold tends to appear on window edges and external corners.
If an apartment remains empty for a longer period, the walls cool down. This leads to condensation of air moisture on the walls and persistent dampness. If the previous tenant did not ventilate properly, the problem is perfect. Believing that you can fix the problem in two weeks with just twice-a-day ventilation is naïve.
You must not forget that your daily life—cooking, showering, breathing—constantly adds new moisture. But to remove the “old” moisture and keep the apartment dry, you need to remove more moisture than you add. Ventilating twice a day is already insufficient for normal living.
You can see this for yourself if the humidity rises to 70% during cooking—that shows you don’t have enough air exchange.
So once again: make it warmer inside the apartment. Every degree warmer allows the air to hold more moisture. And ventilate more often.
I once dealt with a particularly stubborn tenant. He managed to let the entire west wall get moldy. The apartment had been rented out problem-free for 10 years before him. When I arrived there, I was shocked—water on the windows and air so damp you could cut it. Without wiping, I managed to get the windows dry in about five hours. All the heating was turned up (25°C (77°F) in the living room), and every 20 minutes we ventilated by fully opening the windows for 2 minutes. Improvements were visible after just one hour. Wallpaper was completely removed and the mold treated. It took a while until the wall could be re-wallpapered, but most importantly, the tenant understood the issue. After that, there were no more problems.
Regarding measuring moisture: I personally use a Trotec T660, which is quite reliable. There is also a smaller model that costs around 60€ (BM31). For a rough analysis, that should be sufficient. If you find that the walls are damp (which I strongly suspect), it will take a long time for the “stored” water to evaporate back into the room air—and only if there is a moisture gradient toward the air. If you have 40% humidity for a few minutes, the water moves toward the air. At 60%, probably nothing happens initially. So the longer (or more often) you have 40% humidity, the more moisture you remove. Half an hour in the morning and half an hour in the evening is nowhere near enough.
You can calculate for yourself how much water comes out of the walls…
So measure, ventilate, measure, ventilate… The more and the more often, the better. And keep your home properly warm. The warmer, the better.
One more thing: energy loss from ventilation is lower the less moisture you have!
And to put some numbers into perspective: cold air at 0°C (32°F) can hold 5g/m³ of water, air at 20°C (68°F) can hold 17g/m³, and air at 30°C (86°F) can hold 30g/m³. A room with 20m² (215 sq ft) area has a volume of about 50m³ (1,765 cu ft). At 20°C, that room can contain 850g of water. If you exchange that air (ventilate) and replace it with 0°C (32°F) air, the air inside then holds only 250g of water. You have thus removed 600g of water to the outside. This amount of water can be taken up again if the air warms back to 20°C (68°F).
If you also know that a human releases on average 900g of water per day into the environment through breathing and sweating, you can calculate how well twice-daily ventilation helps. Cooking, showering, plants, pets, etc., add even more moisture.
This is also one of the reasons why I now only build properties with mechanical ventilation. With today’s airtight construction methods, natural ventilation is no longer sufficient, no matter what people claim!!!
vacant properties are always a problem. Once the walls are damp, it takes time for the moisture to dry out again. This is completely normal. Believing that ventilating twice a day is enough is unfortunately completely wrong. This misconception has persisted for years but is entirely insufficient in houses built in recent decades (after 1990). Even just the airtight windows prevent air exchange. In the past, you could feel drafts everywhere (my oldest house dates back to 1692—when it's windy, all the candles flicker). When drafts occurred, heating was increased, which in turn led to dry air. That’s no longer the case today, and to make matters worse, there is a “saving is cool” mentality. We are saving ourselves sick.
In principle, two windows permanently tilted open opposite each other would be ideal for air exchange. The problem is that the constantly incoming air cools down the areas around the window, and that is the main reason why tilted ventilation is bad. Moisture condenses on the “cold wall,” leading to mold. This is why mold tends to appear on window edges and external corners.
If an apartment remains empty for a longer period, the walls cool down. This leads to condensation of air moisture on the walls and persistent dampness. If the previous tenant did not ventilate properly, the problem is perfect. Believing that you can fix the problem in two weeks with just twice-a-day ventilation is naïve.
You must not forget that your daily life—cooking, showering, breathing—constantly adds new moisture. But to remove the “old” moisture and keep the apartment dry, you need to remove more moisture than you add. Ventilating twice a day is already insufficient for normal living.
You can see this for yourself if the humidity rises to 70% during cooking—that shows you don’t have enough air exchange.
So once again: make it warmer inside the apartment. Every degree warmer allows the air to hold more moisture. And ventilate more often.
I once dealt with a particularly stubborn tenant. He managed to let the entire west wall get moldy. The apartment had been rented out problem-free for 10 years before him. When I arrived there, I was shocked—water on the windows and air so damp you could cut it. Without wiping, I managed to get the windows dry in about five hours. All the heating was turned up (25°C (77°F) in the living room), and every 20 minutes we ventilated by fully opening the windows for 2 minutes. Improvements were visible after just one hour. Wallpaper was completely removed and the mold treated. It took a while until the wall could be re-wallpapered, but most importantly, the tenant understood the issue. After that, there were no more problems.
Regarding measuring moisture: I personally use a Trotec T660, which is quite reliable. There is also a smaller model that costs around 60€ (BM31). For a rough analysis, that should be sufficient. If you find that the walls are damp (which I strongly suspect), it will take a long time for the “stored” water to evaporate back into the room air—and only if there is a moisture gradient toward the air. If you have 40% humidity for a few minutes, the water moves toward the air. At 60%, probably nothing happens initially. So the longer (or more often) you have 40% humidity, the more moisture you remove. Half an hour in the morning and half an hour in the evening is nowhere near enough.
You can calculate for yourself how much water comes out of the walls…
So measure, ventilate, measure, ventilate… The more and the more often, the better. And keep your home properly warm. The warmer, the better.
One more thing: energy loss from ventilation is lower the less moisture you have!
And to put some numbers into perspective: cold air at 0°C (32°F) can hold 5g/m³ of water, air at 20°C (68°F) can hold 17g/m³, and air at 30°C (86°F) can hold 30g/m³. A room with 20m² (215 sq ft) area has a volume of about 50m³ (1,765 cu ft). At 20°C, that room can contain 850g of water. If you exchange that air (ventilate) and replace it with 0°C (32°F) air, the air inside then holds only 250g of water. You have thus removed 600g of water to the outside. This amount of water can be taken up again if the air warms back to 20°C (68°F).
If you also know that a human releases on average 900g of water per day into the environment through breathing and sweating, you can calculate how well twice-daily ventilation helps. Cooking, showering, plants, pets, etc., add even more moisture.
This is also one of the reasons why I now only build properties with mechanical ventilation. With today’s airtight construction methods, natural ventilation is no longer sufficient, no matter what people claim!!!
Thanks again for the many responses.
We live in NRW. It has been raining every day recently.
Regarding ventilation: We are, of course, trying to air out the rooms much more often now. But you also have to consider that we both work full-time. So basically, ventilation is only possible in the mornings and evenings, although I do air out every time I see the humidity level rise above 60% (for example, before going to bed in the kitchen, I air out 5 times).
By the way, I’m posting here because I was looking for help, as I couldn’t explain these conditions myself. Everywhere you read that ventilating 2-3 times a day by fully opening windows is usually sufficient.
From what I understand, the cause is probably related to the previous tenant / landlord and months or years of incorrect ventilation. I understand that I now need to ventilate and heat more to get it under control.
I will increase the temperature for now. Is an electric dehumidifier worthwhile at this point?
For example, today the humidity in the bedroom only rose by 1.9% to 58.9% during the night, and the temperature increased by 0.4°C (0.7°F).
Should the doors inside the apartment actually be left open or closed?
Regards
bpe87
We live in NRW. It has been raining every day recently.
Regarding ventilation: We are, of course, trying to air out the rooms much more often now. But you also have to consider that we both work full-time. So basically, ventilation is only possible in the mornings and evenings, although I do air out every time I see the humidity level rise above 60% (for example, before going to bed in the kitchen, I air out 5 times).
By the way, I’m posting here because I was looking for help, as I couldn’t explain these conditions myself. Everywhere you read that ventilating 2-3 times a day by fully opening windows is usually sufficient.
From what I understand, the cause is probably related to the previous tenant / landlord and months or years of incorrect ventilation. I understand that I now need to ventilate and heat more to get it under control.
I will increase the temperature for now. Is an electric dehumidifier worthwhile at this point?
For example, today the humidity in the bedroom only rose by 1.9% to 58.9% during the night, and the temperature increased by 0.4°C (0.7°F).
Should the doors inside the apartment actually be left open or closed?
Regards
bpe87
B
Baumfachmann30 Dec 2017 11:19Once again, for those without expertise who are speculating here: this is exactly why experts are called in, but usually only after the building is contaminated with mold spores and the first residents start experiencing health problems. At that point, contractors are happy about extensive renovations.
T
toxicmolotof30 Dec 2017 11:50A constant humidity level of 60% does not necessarily mean that the house will start to develop mold.
bpe87 schrieb:
By the way, I’m writing here because I asked for help, as I couldn’t explain these conditions myself. You often read that airing out 2-3 times a day should usually be enough.Which is basically not wrong, but also not entirely correct... as we are trying to explain to you here.
Tom1607 actually summed it up well...
bpe87 schrieb:
As I understand you, the cause is probably due to the previous tenant/landlord and months or years of incorrect ventilation.No, that doesn’t have to be the case. A flat can become damp within a few days.
bpe87 schrieb:
Is an electronic dehumidifier worthwhile right now?No, it’s only worth it if water is dripping from the ceiling.
bpe87 schrieb:
Should doors inside the flat be left open or closed?The more doors are open, the better the air circulation.
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