Garage problem, mold on the ceiling

Hello community,

I have problems with my garage, the entire ceiling is full of black mold, I have to tell you that it is a flat roof.! Garage 9 years old. Since I heard so many bad things about flat roofs, I suspected that it is leaking and therefore called a professional to redo the roof. As it looked, he just wanted to make money because he wanted 1200 euros just for his labor, without materials, for 10 hours of work to lay 30sqm of roof. Well, that is a story for itself. The fact is, I then educated myself further on the internet and read that it could also be that my roof is not leaking at all!!!!!! But the mold comes from other reasons. P.s. Since I have had this problem for many years, I always ventilated really well this year, so that is not the cause either. Because with poor ventilation, the floor was also wet last year. So I decided this year to leave the door open and behold, the floor is bone dry. But my ceiling still isn’t. This problem with the ceiling happens only in winter!!!! I am sending you pictures, take a look and please help me. Who can tell me what the cause is. I don’t want to redo the roof if it is not leaking at all. Please for tips and help. Whoever can tell me what the cause is... and what I can do. Please, I am desperate, everyone just wants my best and that is only money, money whether it is necessary to do something or not

Hello spale,

there is a possibility that in the area of your garage ceiling a "dew point undershoot" occurs – i.e. water condenses there and mold can develop on this surface. "Dew point undershoot" occurs when the surface of an enclosing room component is too cold for the (too warm?) air in this room.

Example – warm air meets a cold mirror or a glasses wearer comes in winter from outside into a heated room and his glasses fog up. This problem also occurs in apartments, for example when the roller shutter boxes are not properly insulated – then you have no mold in the whole apartment except above the windows – there it is as black as on your garage ceiling.

For a "first analysis," measure the average room temperature in your garage and the surface temperatures of the enclosing room components with an infrared thermometer (hardware store approx. 25 €). If the walls without mold infestation have a higher surface temperature than your garage ceiling, this would be an indication. Then your garage does not have a "leakage problem," but a "building physics problem" that needs to be solved.

Good luck!

Good evening
First, I would like to sincerely thank you for this contribution. And believe me, I have been doing nothing but researching on the internet for days.
I wanted to ask if it would help if I made a cutout in the wall on two opposite sides, about 300mm x 300mm, and installed a ventilation grille. Just to quickly expel the moist air? If the grilles are not enough due to the draft that occurs, I thought about installing a commercial 210mm x 210mm built-in fan on one of the two cutouts. Would that help?
Then I might not even have to insulate anymore, just try with the two grilles and possibly the fan. Please provide information.

p.s I forgot to mention that the garage is connected to the house, not fully aligned but only halfway. And above on this side the ceiling is not black at all. Could it be because warmth comes from the house or from the kitchen?

During the day and light sunshine. The corner where there is no mold, that is, the side connected to the house wall, is not warmer than expected, it is the same. Could it actually be that the mold is caused by the thermal bridge since everything except for the one corner where there is none is moldy. And right at the back at the door (exit) and the full width of the garage door???