High concentrations of impervious surfaces are synonymous with urbanization. A heavy presence of impervious surfaces cause stormwater buildup and excessive runoff. Green roofs are designed to reduce stormwater runoff from roofs and reduce peak outflow. The range of stormwater retention in green roofs is wide, ranging from 40-80%, due to differences in soil depth, vegetation type, and local weather patterns. This study compared two green roofs located in downtown Atlanta, GA, USA, one extensive and one intensive. The extensive roof was found to reach 20% volumetric water capacity, while the intensive reached 25% for the highest capacity event, over a prolonged wetting period. The volume of outflow was higher in an intensive roof due to higher soil volume (23.27 m³) when compared to an extensive roof (10.25m³). A determination of superior retention amongst soil depths was not made due to variable initial soil moisture, with a regularly irrigated extensive roof kept at 10% volumetric capacity for the duration of the study.