Only a small, single digit percentage of building construction volume in Austria correspond with valid building codes and laws. As soon as a house is completed it is very likely that it is not eligible for approval any more. But a building is designed to last for decades or centuries to come – including a long time with no changes in construction to be made. The legal protection of buildings constructed according to rules of law is key, it is referred to the legal term consensus. According to that a lawful existing building is entitled to prevail. The legal obligation to bring historic buildings up to actual codes and laws can become necessary in the event of even minor changes of the existing construction.