It was actually relatively easy to solve... if you know how to do it :D Our site manager then came along at some point with a dehumidifier, which did little to nothing except consume electricity. I eventually got tired of it and hired an expert to determine whether the mold infestation was caused by construction moisture or if there were thermal bridges. The mold was caused by construction moisture, and the expert explained to us how easy it is to solve. Heat the house properly - warm air holds more moisture than cold air - and then do shock ventilation two to three times a day. Through the air exchange, the moisture-saturated warm air goes out and the cold, dry air comes in. You could literally see how the moisture was being removed from the house and the hygrometers dropped. After a week, the walls were dry.