It is a fact, that building is not for eternity. Therefore, in times of scarcity of ressources and global pollution, renovating buildings gets more important. This was the decisive factor to write this diploma thesis. The main goal is the development of renovation concepts of apartment buildings in the area of plant engineering, which can be a decision support to the planner. Important is, to answer the question, if a renovation to plus energy-level can be realised economically. First the regulatory framework for new buildings and renovations as well as perspectives are given. An overview of the historical development of thermal characteristics is given. Afterwards the possibilities to achieve a renovation of buildings with plus-energy level are shown. Therefore projects, with demonstration character are presented. An apartment building in Hütteldorferstraße 252 (Vienna) was basis for calculating 3 different types of energy plants and the results were compared with each other. An accounting of primary energy was made. The results should identify, if a renovation to plus energy-level is possible. Furthermore with this tool, the planner gets a decision support in choosing one of the three types of energy plants. The results of all three energy plants show, that renovating a building to plus-energy level is hard to realise economically. All three types of energy plans show a disbalanced energy balance. Although it would be interesting to check if very efficient domestic appliances together with ecologically usage can balance this energy disbalance or can even produce more energy than used. At this point is has to be said, that only design values were the basis for the calculations. Finally can be said, that the renovation of buildings to plus-energy level should be supported by government even stronger. This specially concerns renewable energy.