Abstract Background Construction industry greatly affect the environment in the aspect of energy consumption and its contribution to global warming. Accordingly, green building construction is significantly growing, which makes it an interesting topic for researchers. Green buildings are defined as buildings constructed according to sustainability standards that keeps the natural environment healthy. However green construction is challenging in the economic aspect and the cost efficiency. Based on the researches, uncertainty is a main reason for cost overrun. In addition, procedures in early stages of the project is of great importance and have influence on the costs. However, further study is needed to identify the differences between conventional and green construction companies regarding uncertainties, cost overrun, and uncertainty mitigation techniques. Purpose The focus of this research is to compare two types of construction companies (conventional and sustainable) in the aspect of uncertainties as inevitable part of risks, it’s effect on cost overrun, and techniques being used in the pre-construction phase to mitigate them. Method Multiple-case study was conducted, and two construction companies were selected of each type. This research is a qualitative study with abductive approach. The empirical data were collected by conducting semi-structured interviews with several positions in each company. Also, secondary data were collected from companies’ archival reports and documents, and from scientific blogs. Conclusion The findings of this research indicate that sustainability creates fields of uncertainties extra to those existing in conventional construction. The study revealed the direct effect of uncertainties on cost, and the indirect effect by generating events which cause overruns in cost. Moreover, Companies work on improving managerial skills in the preconstruction phase to mitigate the effect of uncertainties and to reduce probability of cost overrun occurrence in both sustainable and convention construction companies. While in sustainable construction, additional techniques and efforts are needed as technology, artificial intelligence, and hiring external resources and staff.

The subjects of this thesis are low-energy and passive houses. The main objective is to compare the acquisition costs and operating cost of the low energy and passive houses with conventional construction of houses offering the real estate market, respectively evaluating of investments in energy-efficient buildings. Furthermore, the work focuses on the history, properties and basic problems of designing energy efficient buildings with subsequent by an assessment of the advantages and disadvantages of their implementation. Klíčová slova