This study aims for the assessment of the indoor air quality in sustainable, energy-efficient buildings (houses and schools), typically equipped with mechanical ventilation systems. The main focus is the determination of the influence of outdoor air, of the ventilation system (type, usage, maintenance) on the indoor environment.

Designing energy-efficient buildings implies a reduced energy use of the building, considered over its complete life cycle. The most efficient strategies to reduce the energy consumption are a better building insulation and an increased air tightness. Doing so, generated heat is kept inside of the building envelope, leading to a positive effect on the energy consumption.

Increased insulation and air tightness in newly built houses and schools however imply a very limited natural ventilation through openings and cracks in the building envelope in this type of buildings. Since sufficient building ventilation is indispensable to maintain the indoor environment healthy, these buildings need a ventilation systems.

Ventilation systems offer the advantages of a controlled air exchange rate in the building, but it does lay the responsibility of a correct use and maintenance in the hands of the users/occupants. In fact building owners, and occupants become responsible for the generation of a healthy indoor environment.