A green roof requires regular irrigation until the plants have become established. Thereafter the plants need to be irrigated as and when necessary. This maintenance is determined by the type of vegetation, the depth and drainage characteristics of the soil and the prevailing atmospheric conditions. Opportunities exist for irrigation using water collected in the gutters of the roof and adjacent roofs and grey water from kitchens and bathrooms. Fertiliser and compost need to be added during the growing season to keep plants in tip top condition. Planted roofs need to be weeded, because a common problem is the germination of wind and bird dispersed seed.
From a plant point of view it would be good to have at least 75 species of plants on each roof. This will give a softer and more colourful appearance to each roof instead of just a few species. Plus add to the biodiversity that is missing at ground level due to the high browse rate of plants by the severe overpopulation of Bushbuck. Plant the roof up with small plants not huge specimens so that the plants grow into the situation of shallow soil.
On the issue of soil depth we all agreed that the maximum depth would be in the order of 150mm and down to about 75mm deep nearest the full bore drains so that there would be no danger of flooding or overtopping the slab under a severe downpour. All full bore drains to be completely open with not obstructions and a 30mm stone chipping cordon around each dran to a diameter of 500mm so that no plants or roots could obstruct water entering the drain.