Active ventilation
Passive ventilation alone will not provide enough air exchange to remove moisture from wet areas such as bathrooms, kitchens and laundries. In those situations, an air extraction system or other form of active ventilation is needed to remove moisture.
Other forms of mechanical ventilation are also available and may be useful if a building is very airtight, or security or other concerns make a passive solution unviable. Heat recovery systems in particular require very airtight buildings and user education to work efficiently.
For more detail, see active ventilation.
Building Code