A roof garden is any garden on the roof of a building.
The garden may be on the roof of an autonomous building that takes care of its own water and waste. The related idea of a living machine is based on the most basic mode of gardening: dumping wastes (compost and sewage, appropriately broken down, usually in some specialized ditch or container) on the soil, and harvesting food which, when processed, generates compost, and when eaten, generates sewage. In most of the world, this kind of very tight closed loop gardening is employed, despite certain health risks if modern technologies and methods are not employed.
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