ᐅ Mold inside a 3-year-old house at the wall/ceiling corner

Created on: 20 Nov 2019 16:18
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Pluto1977
Hi,

I need some advice. In our house (3 years old, solid construction, 36.5cm (14 inches) Poroton blocks), there is mold forming in one room at the corner where two walls (both exterior walls) and the ceiling (upper floor under the flat roof) meet. There is no mold anywhere else in the house, and we ventilate the room daily.

I had the roofer check the site, and they removed the roof down to the concrete layer, but everything is dry there.

Now we’re really stuck... Everyone is puzzled. What could be causing this problem?

Thank you and best regards
Mycraft20 Nov 2019 19:55
Too little ventilation. Well, and inevitably also heating...
seat8820 Nov 2019 20:33
But at 19.3 degrees Celsius (66.7 degrees Fahrenheit), it can hardly be considered underheating...
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Bookstar
20 Nov 2019 20:39
Something is wrong here, is that a basement? During the heating season, the humidity is usually around 40 percent. This likely means that water is actually entering from outside somewhere— in other words, a leak!
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Tego12
20 Nov 2019 21:37
It is more likely that simply not enough ventilation is provided. If there is no controlled residential ventilation system or purely mechanical solution such as trickle vents, airing the room once a day is far from sufficient... Nowadays, all houses are airtight. During the heating season, indoor humidity does not decrease compared to summer,... If the house is occupied without regular ventilation, the humidity will also increase...
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nordanney
20 Nov 2019 22:27
Pluto1977 schrieb:

2. I just measured the temperature on the wall. It is 2 degrees cooler (17.2°C (63°F) compared to 19.3°C (66.7°F)) than in other areas. How a thermal bridge could form there, I don’t know, but I’m not an expert.
I recently had the same issue in an apartment (not my own). The corner was simply colder, which caused mold. You can ventilate all you want, but it doesn’t help. The insulation is somehow insufficient there, for whatever reason = thermal bridge.
Possible solution: Insulate the inner corner with calcium silicate boards. That should prevent mold from forming.
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Zaba12
21 Nov 2019 05:50
I also find 19.3°C (66.7°F) feels quite low. We always ventilated the apartment well, but last year we tried to start the heating season at the beginning of November. And suddenly, due to heating too late, mold or mildew appeared on the roller shutter box, whatever you want to call it. Heating too little is just as bad as ventilating too little. After we removed the stains and heated properly, everything was fine again.