A green roof is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane.
Green roofs usually do not involve construction of complex drainage and irrigation systems. The use of “green” refers to the growing trend of environmentally friendly and does not refer to roofs which are merely colored green, as with green roof tiles or roof shingles.
There are different ways in which green roofs are constructed. Container gardens on roofs is one of the type of green roof, where plants are maintained in pots, are not generally considered to be true green roofs, although this is an area of debate. Rooftop ponds are another form of green roofs which are used to treat greywater.