The existing public utility building belonging to the Forest Experimental Station of the Poznań University of Life Sciences, due to high energy consumption and related costs, has qualified for deep energy modernisation or consideration for the construction of a new building. One of the goals is to achieve carbon neutrality and have a positive energy balance. The article uses the hybrid DEMATEL-AHP/ANP-VIKOR method. The methodology used is distinguished by the creation of a set of decision-making criteria and the identification of the relationship between them, which is determined by conducting a survey of a group of experts using the Delphi method, as well as determining the preferences of the decision-maker using a survey of the target group using social research. Two different models of the decision-maker’s preferences have been developed, taking into account the selected decision criteria, and four acceptable technical solutions have been identified. As a result of the calculations performed, a ranking of the solutions has been developed, from the most preferred to the least accepted. Variant 3B has been identified as the best solution with respect to eight evaluation criteria for both of the adopted models of the decision-maker’s preferences. The ranking index Ri coefficient for this variant ranged between 0.733 and 0.901, while for the other variants, it was lower and amounted to between 0.106 and 0.274 for variant 1, 0.166 and 0.290 for variant 2 and 0.403 and 0.437 for variant 3A. The methodology used for the case study has proved to be applicable. The presented methodology can be used to design new buildings (not only residential) with almost zero energy consumption, as well as those with a positive energy balance, and can also be used for deep energy modernisation. In this article, it was applied for the first time to the energy modernisation of an existing public building.