Having a green roof or a wall is more popular lately because of more benefits people get by having it. Green roof is basically excellent isolation and also for reducing storm water runoff, is excellent for energy use and for the heat island effect. The benefits of green walls are similar: reducing the urban heat island effect and smog, it can clean the outside air of pollutants and dust, also it cleans the interior air space, acts as a sound proof barrier.
The layers that any wall or roof greenery has are similar and probably the same: vapor control, thermal isolation, support panel, waterproof root repellent, drainage, filter membrane, growing medium. Everything more is showed in the images bellow.

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