Planted roofs contribute positively to the improvement of the thermal performance of a building. They block solar radiation, and reduce daily temperature variations and thermal ranges between winter and summer. In this paper, a calculation has been done, using a stationary method, in order to determine the thermal behaviour of the planted roof and the way it influences the thermal protection of the building, in accordance with Greek climatic conditions. Planted roof elements with different heights of plants and different drainage layers are calculated and a comparison between a ban roof and a planted roof is made. All sections are calculated with and without thermal insulation. The results are illustrated in figures, in which the temperature of the layers of the planted roof is presented for both winter and summer. The planted roof contributes to the thermal protection of a building, but does not replace the thermal insulation layer.