The priority direction of modern architecture and construction is energy efficiency and energy saving. Thermal performance elevation and thermal comfort indoor climate supporting are necessary during all life cycle of the building — at design, construction, operation and reconstruction of buildings. This problem is especially actual for the cultural heritage objects which are of historical and architectural and art value. Preservation of the history and the cultures monuments which are national property, it is important both for present generation, and for descendants. In this article the thermal performance elevation problem solution at St. Sergey Radonezhskiy temple reconstruction in Volgograd is given. On the basis of visual and tool inspection numerous defects of external walls of additional building to the temple by construction which can't provide reliable and safe conditions are revealed. The assessment of hollow masonry thermotechnical parameters by use of temperature and moisture mode method with consideration for edge effects zones is executed. By results of calculation it is established that application according to the design as mineral wool insulation provides minimum admissible requirements for thermal performance. However the lowest value of heat transfer performance uniformity factor testifies to the inefficient design constructive consideration of external walls. The settlement assessment showed that application of monolithic polysterene concrete, according to the author idea, considerably increases the heat transfer performance uniformity factor of external walls. The specified recommendation is realized in practice in 2013.