Insulate condominium with moldy corners afterward

I once had a similar situation where the bedroom was on the north-facing exterior wall. And I also had mold. Besides airing out and heating a bit, I managed it by bringing more fabric into the room. I discovered by chance (disposed of a laminated wardrobe and replaced it with an untreated solid wood shelf with curtains) that wood and/or fabric helped to regulate the humidity. They apparently absorbed enough moisture to take away the basis for the mold. Maybe not a substantial solution, but at least something.

That is basically not a bad idea and might perhaps temporarily solve the problem with even more heating (ok, the quality of sleep would suffer enormously).

Since we want to rent out the apartment in 1-2 years, the cause needs to be fixed. I can’t put in the rental contract that tenants have to go home at noon from work to air out and also heat to at least 24 degrees. Also, only solid wood furniture would be allowed…

That is simply our problem :/

Is the picture deceiving me or does the wall already look really soaked? You say it’s a typical thermal bridge but the expert could not find anything?

With 20 degrees and airing twice a day, this will not be brought under control. More heating and airing is needed here.

No, it’s not deceiving. Those are water stains from the last painting, which depending on the humidity level in the bedroom appear more or less visible. The spots themselves are dry. I measured with a moisture meter. It’s also only on these 0.5 sqm of wall surface on the exterior wall.

According to the expert, these corners are always the coldest due to building physics and thermal reasons. Therefore, this is not a defect, but “normal.”

Regarding heating and airing more, see above. Especially in the future, no tenant will do that.

We have to get to the core of the problem and not fight it with various measures that are certainly acceptable for a homeowner but not for a future tenant.

What do you think about insulating plaster + wallpaper + additionally insulating paint or lime/silicate paint?

My apartment is located under the roof. After the roof was insulated, everything only got worse. Without knowing anything about insulation, I would say that insulation is an overall project for the entire apartment. Otherwise, you create thermal bridges elsewhere. I told my tenant that he should best not place any furniture against the relevant wall, and if he does, then with sufficient distance from the wall.

We moved into these in April 2018

According to the floor plan, however, that is not also the year of construction (???)

Bathroom. Helios exhaust motor. Keeps our bathroom very dry. Kitchen, extractor hood must vent cooking fumes. Out of the house.

Has the wall temperature in the corner already been measured with an infrared thermometer at different points and compared with the other exterior walls in relation to the respective room temperature? That could possibly provide further insights.

My apartment is located under the roof. After the roof was insulated, everything only got worse. Without knowing anything about insulation, I would say that insulation has to be a comprehensive project for the entire apartment. Otherwise, you create cold bridges elsewhere.
I told my tenant that it is best not to place any furniture against the affected wall, and if so, then with sufficient distance from the wall.

There is no furniture in the affected corner.

According to the floor plan, this is not also the year of construction (???)

Year of construction 1992. Originally, 2 residential units were planned (which can still be clearly seen in the floor plan). Afterwards, it was made into a single residential unit.

Bathroom. Helios exhaust fan. Keeps our bathroom very dry.
Kitchen, range hood must expel cooking fumes. Out of the house.

We already have both in the bathroom and in the kitchen.

Has the wall temperature in the corner ever been measured at various points with an infrared thermometer and compared to the other exterior walls in relation to the respective room temperature? That might possibly provide further insights.

The expert did that. He could not detect any structural defect at the affected corner. Nevertheless, the dew point is apparently quite high there, so moisture condenses quickly.