In decentralised storm water management green roofs play a vital role. Nevertheless questions remain concerning the runoff quality for nutrients and herbicides used against root penetration. In this study monitoring is conducted on two 18 year old green and gravel roofs comparing runoff quality based on concentrations and substance loads. The results indicate that runoff concentrations do not differ for total suspended solids (TSS) and total phosphorus (TP). Nitrate (NO3N) and total nitrogen (TN) concentrations are clearly reduced by the green roof (TN green roof: 1.14 mg/L, gravel roof: 2.99 mg/L, n=7), given plant uptake of atmospheric nitrogen. In contrast, organic indicators chemical oxygen demand (COD green roof: 28.1 mg/L, gravel roof: 16.1 mg/L, n=11) and total organic nitrogen (TON) are higher in green roof runoff, possibly from soil leaching. However, total substance loads for 11 sampled storm events are lower by a factor of 0.8 to 0.2 (TSS, COD, TP, TN, TON) for of the green roof compared to the gravel roof, given their different hydraulic behaviours. Regarding herbicides, Mecoprop is still found in relevant concentrations from 0.08 to 6.59 µg/L in the green roof runoff, exceeding the EU threshold for pesticides in surface water bodies of 0.1 µg/L.