A green roof or living roof is a roof of a building that is partially or totally covered with plants. It may also include layers such as a root barrier and drainage and irrigation systems. Container gardens on roofs, where plants are in pots, are not generally true green roofs. Although, this is debated. Rooftop ponds are another kind of green roof which are used to treat greywater. Vegetation, soil, drainage layer, roof barrier and irrigation system make up a green roof.