The air-tight building envelopes of new buildings and modernised properties require additional ventilation measures

In renovated old buildings or new buildings that comply with the provisions of the current Building Energy Law (GEG), only a minimum air exchange takes place through the building envelope. Paragraph 13 of the Building Energy Law (GEG) stipulates: “Buildings to be constructed shall be designed in such a way that the heat-transferring enclosing surface, including the joints, is permanently sealed impermeable to air in accordance with the recognised rules of technology.” The practical consequence is: A complete air exchange, only through leaks in the building envelope, takes at least ten hours. Under these circumstances, window ventilation would have to take place much more frequently and for longer periods than before in order to achieve the mandatory requirement of DIN 4108-2 by this means alone.

It can be assumed that many occupants do not adhere to such specifications, for reasons of convenience, and that this is not even feasible in the case of longer absences, for example, while on holiday. However, insufficient ventilation often results in mould growth, which in turn can lead to considerable structural damage and be harmful to health (can cause allergies).

For this reason, for years the case law of the higher courts has recognised inadequate ventilation as a construction defect for which architects and construction companies are liable. A new building or modernisation, should therefore be planned in such a way, that no damage occurs to the building during normal ventilation behaviour by the occupants. This is also required by paragraph 13 of the Building Energy Law (GEG): “Regulations under public law, on the minimum air exchange required for the purpose of health and heating, remain unaffected”. This is particularly important in the case of rented properties, as in the opinion of many courts, tenants cannot be obliged to “ventilate beyond a normal amount”. On the contrary: If the required room air quality is not ensured without special measures taken by the tenants - assuming a usual manner of living - this can lead to a rent reduction and, in serious cases, to lease termination as well as compensation for damages.