This paper deals with the problematics of the surface temperature of flat roofs, where the waterproofing layer is used as polymeric waterproofing membrane of softened PVC. Currently, it is possible to encounter defects on flat roofs due to the high surface temperature of the waterproofing layer. The consequence of such a high surface temperature is, for example, the sublimation of the thermal insulation of the foam polystyrene. The paper focuses on the influence of the color of the plasticized PVC membrane on the surface temperature. The aim of this paper is to determine the maximum surface temperature of a polymeric PVC membranes in the dependence on color on the basis of experimental measurements and furthermore, to determine the maximum temperature on the surface of the thermal insulation under PVC polymeric membrane. Measurements were taken during a warm summer day. Used samples were represented by polymeric membranes in green, gray, red and brown colors. Mineral wool was used as a substrate under the polymeric membrane.