Green Roofs - more than just bringing beauty
Green roofs are a rapidly growing trend across the world’s cities as policy makers become increasingly committed to improving their urban environment:
- In addition to bringing beauty to grey places and enhancing biodiversity, green roofs help cool inner city areas which can be up to 7oC hotter than their surroundings and they ease stress on municipal drainage systems by cuttings rainwater run-off.
- Green roofs also improve residents' health by improving air quality as they absorb dust particle pollution and consume CO2.
- According to different studies, researchers estimate that vegetation (sedum) on green roofs can capture airborne particles such as smog, heavy metals and volatile organic compounds in amount of 0,2kg of airborne particles per 1m² of a green roof every year (Peck, S. W., M. Kuhn, et al., 2003).
Picture 1: Sources of PM10 and PM2.5 airborne particles
Source: © European Environment Agency, 2014
- Further more considering all factors, 1m² of a green roof can directly (consumption by vegetation) or indirectly (through energy saving) help decreasing CO2 emissions for 5 to up to 7kg per m² yearly.
Picture 2: Direct CO2 absorption by different sedum spieces on the roof in Berlin, 2012Source: IASP Institute, Berlin (Germany)
These reasons are cited again and again by cities across North America, Europe and Asia that are accelerating the installation of green roofs through new laws or financial incentives.
Green Roofs - a growing trend in Europe
In Copenhagen (Denmark) green roofs have been mandatory on all new roofs with a pitch under 30 degrees since 2010.
Stroll through the streets of the Danish capital and you’ll find green roofs on all types of building from cycle shelters, schools and parking spaces to huge public buildings such as the National State Archives.
“Due to the growing challenges of cloud bursts and flooding, green roofs are a growing global trend,” says the city’s Chief City Architect Tina Saaby Madsen.
“In Copenhagen the idea is to combine practical use when heavy rain hits, the biodiversity green roofs offer and the possibility of more nature in a big city that is increasing by a thousand new inhabitants every month."
“Furthermore it has a great effect on cooling buildings and that helps in our goal of becoming the world’s first CO2-neutral capital in 2025.
Other European cities have their own green roof policies
Munich (Germany) has mandated the inclusion of vegetation on all flat roofs larger than 330 square feet.
Basel (Switzerland) has had similar laws since 2002.
Rotterdam (Netherlands) offers a Green Roofs Programme that includes generous financial incentives and London aims to increase green space — including green roofs — by at least 5% by 2030 and an addition 5% by 2050.
London (UK) Plan Policy states: “If London is to adapt to the extremes of climate change, living roofs are key. They can keep the city cool while at the same time reducing energy use and carbon dioxide emissions and reduce flood risk by absorbing heavy rainfall.”
Green roof laws are gaining momentum backed up by scientific evidence.
In France, proposed legislation introduced in March 2015 was initiated among others also by a study how dust particles in the air have significant impact on a death rates based on respiratory diseases.New green roof legislation demands that rooftops on new commercial buildings in France must either be partially covered in plants or solar panels. If approved by the French administrative process it will be the first law of its kind on a national level.
Europe is not alone in demanding more green roofs
Toronto (Canada) was the first city in North America to introduce a law to govern their construction.
The 2009 legislation requires that any new development over 2,000m2 in gross floor area must include a green roof covering between 20 and 60% of the roof.
The reasons? The city’s Technical Design Guidelines state: “Green roofs reduce urban heat island and associated energy use, manage stormwater control (run-off) — reducing pollutants that enter our waterways — and improve air quality.”
According to the annual Green Roof Survey the city installed 775,216 square feet of green roofs (more than 70.000 m2) in 2014 alone.
Many US municipal planners are now so keen to improve their infrastructure that they are incentivising the installation of green roofs with rebates and tax credits.
As a result cities such as Philadelphia, Chicago, New York and Denver saw the installation of between 300,000 (cca. 28.000 m2) and 600,000 square feet (cca. 55.000 m2) of green roofs last year with Washington DC recording a staggering installation of 1.2 million square feet (more than 100.000 m2).
In Asia, it’s a similar story.
The Singaporean government has introduced the LUSH Programme (Landscaping for Urban Spaces and High-rises) to financially incentivise the creation of an extra 50 hectares of skyrise greenery by 2030,
in China’s Shanghai the municipality is offering subsidies leading to 1.45 million square meters of green roofs by 2012.
And finally, Australian city planners in Melbourne and Sydney have been actively promoting the installation of green roofs for years.
The reasons are as familiar as they are practical. “Green roofs absorb and retain rainwater and filter particulates and pollutants,” say Melbourne municipality’s Growing Green Guide.
It seems as far as cities are concerned, the trend for vegetative roofs shows no signs of slowing down.
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Or check the above mentioned documents on different Cities' Green Roof incentives, legislation and trends below.