Green roofs are increasingly a norm in building design. Policies for green roofs feature in the Local Plans of three of the principal urban centres in which MKA Ecology are based; namely Cambridge, London and Milton Keynes.
These water-retaining, climate-regulating, wildlife-friendly features are being written into local planning policy in increasingly stronger terms. For example, the recently adopted Cambridge City Local Plan (October 2018) now stipulates that development is only permitted where all flat roofs are created as either green or brown (biodiverse) roofs. The Plan also states that green roofs should be widely used in large-scale new communities.
A majority of green roofs currently consist of sedums or succulents, but as these are most often non-native species, they have limited potential for supporting our native wildlife. Roof habitats which use native plant species and wildflowers have significantly greater biodiversity value, and can deliver the same water retention and climate regulating services as sedum roofs. They also often require less ongoing management.
Furthermore, there is potential to mimic surrounding habitats by appropriate selection of substrate and locally-sourced seed mixes. For example, the London Borough of Sutton’s Local Plan (February 2018) recommends that green roofs should simulate the grassland habitats of the North Downs. The chalky soils surrounding Cambridge City support locally and nationally rare calcareous grassland habitat, which in turn supports several rare plants. A roof rich in calcareous plants would make a significant contribution to conservation of this rare habitat, as well as supporting a host of other rare chalk grassland specialist invertebrates.
Native habitats do in some cases take longer to establish than sedum mats, but the benefits more than outweigh the waiting time. The green roof on the David Attenborough Building in Cambridge is one such example of a slow-establishing rooftop ecosystem – one which is now flourishing and paying dividends for native pollinators.
Our biodiversity experts at MKA Ecology can provide expert ecological and horticultural advice on species selection, biodiversity enhancement, maintenance and monitoring of plants in a green roof environment. If you would like to learn more about our green roof services then please contact us.