First and foremost, the green roof must be watertight and the waterproofing must be suited to the unique demands found in a vegetative environment. The waterproofing must be root resistant, chemically stable, and able to withstand ponding water. Waterproofing root resistance is tested using a 2 year greenhouse test developed by the German FLL. If the waterproofing has not been tested or has failed the root resistance test an additional root barrier is required.