In the article are presented the problems which has been placed during the design of boiler building’s foundation. As the key issue a proper subsoil recognition and its potential variability were indicated. In case of Turów power plant present in the substrate is granite with varying degrees of weathering. This eliminates any necessity of subsoil reinforcement. On the other hand, enforced conditions by the plant’s technology suppliers of foundation settling not exceeding 15 mm becomes a primary criterion for selection of foundation slab dimensions. Another important issue is a proper computation and presentation in a suitable manner of substrate rigidity coefficient on a computational model. Attention was directed towards assembly loads. They may be a deciding factor in terms of outer basement walls and outer column plinths, which also constitute as wall bracing. The article indicates many external factors necessary to take in to account during the design. Without understanding them it is not possible to obtain the correct final results. Keywords: foundation, power plant, boiler house, subsoil.