The goal of this paper was to optimize the building envelope and technical equipment in the building through the mitigation of the global cost value, and then to evaluate the influence of the chosen assumptions on the primary energy index. The analyses carried out using global cost method allow for finding the cost optimal solution but only for the some range of primary energy index variability. In order to find the optimal solutions it was proposed to use the multi-criteria optimisation, assuming the following as basic criteria: a global cost value and investment prices increase (economic criteria), a primary energy index (energy-related criterion), an emission of carbon dioxide (environmental criterion). The analysed case study refers to the technical solutions for the residential buildings with the usable energy demand at the level of 40 and 15 kWh/m2/a. The presented method might be applied to different types of buildings: those being designed and those being the subject of the thermo-modernisation. The results demonstrate that the proposed model allows for classification of the alternative technical solutions regarding the designing process and the building’s technical equipment. The carried out analyses indicate the economic possibility to achieve the low energy building standard and show the need to concentrate the activities related to the installation technology and used energy source.