The problem of reducing energy consumption maintained buildings became a prerequisite for the improvement of energy-saving technologies. Energy efficiency and reduction of costs in the operation are realized by reducing heat loss through the outer covering. The innovative technology of green roofs has attracted increasing attention due to its engineering, warmth-economic, environmental benefits. Energy saving is achieved due to the high thermal insulation properties of the green roof. In this article structure of green roof and typical roof structure are considered as a covering for two buildings with different relations of square of covering to square of enclosing structures in Saint Petersburg. By results of the thermotechnical calculation are assessed the energy and economic efficiency of buildings with application of green roof technology.