In Lithuania, there are about 40 million square meters of flat roofs, such as roofs of apartment houses, public and industrial buildings and other. Subject to the construction of the roof, the building can lose as much as up to 30-35% of the heat through the roof partition. Therefore, the renovation of roof is among the primary works in the renovation of buildings. Condition of flat roofs which were installed 20 or more years ago is poor, as there were used old technologies, poor materials and insulation of roof does not meet today’s requirements. Today about 70% of all roofing works consists of the renovation work. However there are often made mistakes, not used options of roof’s modernization. The purpose of this work is to analyze the renovation techniques of flat roof used in Lithuania and typical mistakes of renovation, as well as describe the emerging option for modernization of flat roof.