John Ball Primary School gave us a chance to create a green roof designed not only for its aesthetic appeal but also for its biological diversity.
Although these two issues were the driving force of the design, there was also an issue of weight. To get around this, we used a specialist lightweight substrate in order to maximise the depth we could use. That way the roof can support a wider variety of plant life which will in turn attract a higher diversity of animal species to the area.
A key factor to take into account when planning a bio-diverse roof is ensuring that one species does not take over which will lead to a decrease in both species richness and evenness. To avoid this we contour the soil, so that at different areas of the roof there are varying depths of growing medium. This allows different species to thrive in different locations on the roof and avoids a monoculture developing.
Added to this are the piles of untreated hardwod logs you can see. As these rot, they provide a habitat for a large range of invertibrate life. These insects attract predators such as birds and bats, which further increases the bio-diversity.
Although this is a brown roof, which are often left to self seed with natural flora, we sowed a specialist London wildflower mix, as well as a cornflower mix of seeds to speed up the rate of establishment of plants on the roof. When combined with our irrigation system this will allow the roof to germinate in a matter of weeks and start to provide sources of nectar for pollinators such as bees and butterflies in the coming summer months.