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

Hi,

I need some advice. In our house (3 years old, solid construction, Poroton bricks 36.5 cm), in one room at the corner of two walls (both exterior walls) and the ceiling (upper floor under the flat roof), there is mold formation. Otherwise, there is nothing in the house and we ventilate the room daily.

I have had the roofer on site and they opened the roof down to the concrete, but everything is dry there.

Now good advice is expensive... Everyone has a question mark over their heads. What could the problem be?

Thank you very much and best regards

Moisture can come from the inside if the corner is "cold" for some reason. Measure the temperatures on the walls.

Heating and ventilation... that should solve the problem.

Daily ventilation can mean anything, and even with daily ventilation, mold occurs if heating is too low and/or air exchange is insufficient.

Moisture usually comes from inside in such cases, through humans/animals (mere presence is sufficient) and plants. The exterior walls are colder than the rest -> condensation -> mold

Sufficient heating + ventilation = no cold walls = no condensation = no mold.

This is easy to clarify. I assume a thermal bridge. Measure the spots where mold grows with a laser thermometer. Important when outdoor temperature is <5 degrees, even better if colder.

Then measure at another spot where there is no mold to have a comparison value.

You determine humidity and room temperature with a normal measuring device for 20 euros. Then you can calculate the dew point, and if this is undershot, you will have mold.

The solution can be to heat more and ventilate properly or to insulate the spots from the outside, if possible. Alternatively, insulation can also be done from the inside.

How is the furnishing in the corner? Often, furniture prevents good air circulation.

Hi,

thank you very much for your answers. Regarding the questions:

1. There is no furniture there
2. I just measured the temperature on the wall. It is 2 degrees colder (17.2 compared to 19.3) than in other spots. How a heat bridge could form there I wonder, but I’m no expert.
3. The humidity just gave me a shock: 67%. It is a "baby room" that is actually only used by a child at night (not anymore now because of mold). So I wonder where the moisture is coming from. I would get a dehumidifier now or what do you think?

Best regards and many thanks