The benefits of green roofs include cheaper energy bills (less winter heating and summer air conditioning needed), better sound insulation, abatement of the urban heat island effect, and improved air quality (plants can capture particulate matter and absorb harmful gases – including nitrogen dioxide).
Another important feature of green roofs is that they can reduce flash flooding by soaking up heavy rainfall and then releasing it more slowly. Finally, green roofs offer food and shelter to bumblebees, butterflies and moths; and even nesting spaces for birds. The UK green roof market is currently expanding at a rate of 17% each year.
Almost every flat roof in Stuttgart city-centre has a mature green roof. Most of them use slow-growing, drought-tolerant vegetation such as sedum, but there are also rooftop gardens on many of the commercial premises. The city authority has made it a requirement that all green roofs retain 70% of the rainfall that hits them to manage stormwater flooding.
The photo above shows a rooftop park on top of a shopping centre in the town; it is open all day and evening for residents and shoppers. The city also has a health centre whose roof features a small running track for physiotherapy patients to use for rehabilitation.
Clapham Park, South London
A bio-solar roof combines vegetation with solar panels, as can be found on top of this new social housing development in Lambeth. The green roof blends a mix of 49 native wildflowers with PV solar panels that generate 10% of the residents’ electricity needs. Recent research in the USA shows surrounding PV panels with plants boosts their efficiency by preventing overheating.
Utrecht has planted sedum roofs on 316 of its bus stops. In Portsmouth there are green roofs on the P&R bus stop in Tipner and the public toilets near Canoe Lake.