Green roofs improve the quality of life in urban areas. However, radicides such as Mecoprop are needed to ensure that they function optimally. These protect the roofing membranes from root penetration. But how do these agents affect the environment? The amount of Mecoprop released by green roofing membranes was measured by Fraunhofer IBP scientists in a field test and two different laboratory tests. Commercially available roofing membranes containing different concentrations of the various Mecoprop esters were studied. While the laboratory tests were carried out under defined test conditions using small-format samples of the roofing membranes, the 18-month outdoor test used complete roof structures 1 m² in size. The roofing membranes were exposed to the weather both with and without extensive greening.