If the top floor is found to be leaking, first find out the leaking point, lift the waterproof layer of the roof, dry it, then carry out waterproof repair, and do a closed water test for at least 24 hours, with a storage height of at least 2-3 cm. If you don't follow the above steps, the water vapor in the waterproof repaired floor can't be discharged upward, but can only be discharged downward slowly (that is, into your room). According to the degree of water leakage at that time, it will take at least 1-2 years to completely drain. Especially in the wet season in summer, a moisture regain point (that is, the mildew point you said) will be formed on the surface of the ceiling in the part with more water vapor and humid air.
If you want to speed up the discharge of water vapor, the general simple method is: drill more holes in the leaking part last year (use electric drill or impact drill, be careful not to exceed the thickness of the floor to prevent the waterproof layer of the roof from being drilled through), and open the window for ventilation for about half a month. This treatment method has a good treatment effect in the spring and autumn dry season. The drilled eye is plugged with expansive cement and can be decorated after drying. If you have more questions, you can click the ID for consultation.