In addition to structural defects, insufficient circulation of air and changes in the microclimate caused by failure to clean ventilation systems can lead to a mould population.

Mould is promoted by the combined effect of failure to clean ventilation systems and the installation of PVC windows. Vinyl windows are very practical due to their good seals, but do not allow air to penetrate. Thus natural ventilation in rooms is impaired, which previously took place around the frames of old windows.

Mould leads to a number of health problems – fatigue, headache, cold and cough, bouts of fever, irritation of the eyes, throat and skin, increased incidence of upper respiratory diseases due to lowered immunity. There are often lung, sinus or middle ear infections, allergies and asthma. Tumours and brain damage may also be caused by some types of mould.