The paper presents the results of the simulation of the energy performance of underground buildings variously insulated, in two different climates. The long-term unsteady thermal processes between the building and surrounding soil are considered together with the heat transfer at the ground surface throughout the year. Presented results include the time and space distribution of the heat flow between the building and surrounding soil at different time intervals and during the whole year for various insulation patterns, and the heat flows through the ground surfáce. The isotherms around the buildings in winter and summer, for various insulation patterns are also presented. The conclusions are drawn.