In recent years, poor indoor climate has caused health problems for building occupants. Sometimes these problems have been so serious that these buildings have, quite rightly, been labelled sick buildings.Today, there is good evidence in some areas as to why such problems arise. Unhealthy substances given off by various building materials, the existence of mould and general air pollution are the main causes. Another important factor is the high level of humidity in buildings and indoor air.In general, the most important way to remedy the problem is to improve ventilation. Unfortunately, many studies have shown that poor upkeep and maintenance have led to a decline in the performance of existing ventilation systems. If, in the future, we do not look after our ventilation systems properly and adapt operation and maintenance to current user habits, then even more buildings will become problem buildings. More people will suffer health problems unnecessarily.Briefly this is why the Swedish Parliament and Government decided, in complete political unanimity, to introduce regulations on compulsory inspection of ventilation systems. This is also why the National Board of Housing, Building and Planning has issued general guidelines for performance checks on ventilation systems.