First results concerning the incidence of different types of extensive green roof structures on the quantity and quality of runoff are presented. The effect on substrate thickness, type of drainage layer and vegetation on these emissions is discussed. The data have been acquired within the field of the TVGEP project, on an experimental test bench in Paris area. Runoff measurements confirm the ability of green roof to decrease runoff volume, with annual runoff coefficients inferior to 0.5. At the event scale, this retention capacity is however strongly variable and depends on rainfall depth and soil moisture condition. Important levels of conductivity, organic carbon and phosphorus concentrations have been measured in the green roof runoff, which should be taken into consideration if the runoff waters are collected into small detention ponds or small creeks. Pollutant loads emitted are strongly dependent on hydrologic behavior of the green roofs. Further data is needed for an accurate evaluation of annual pollutant loads.