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A ‘living roof’ can make a vivid green statement. The 1,700 square metres of living, breathing greenery on two long sweeping slopes of roof are the crowning glory, for instance, of the ‘8 house’ in Copenhagen’s Oerestad district. This mixed-use development, combining offices and 540 dwellings, has just won the housing category in the 2011 World Architecture Festival Awards. It’s also been designated the ‘best green roof in Scandinavia’. This is high praise indeed, since Germany and Scandinavia pretty well lead the field in this fast-growing contribution to more sustainable cities.
New York’s equivalent, the Via Verde (Green Way) social housing project due to open in early 2012, offers another beacon for sustainable urban renewal, bringing rooftop gardens to the heart of the South Bronx.
As these and other award-winning buildings boost their profile, green roofs are increasingly recognised as neither wacky nor whimsical. Their environmental, social and economic credentials are also alerting a wider audience that they can be a smart solution even for the most modest schemes. New build or retrofit, sheds, home extensions, houses, schools, and all kinds of public and commercial buildings are starting to show the benefits.
In Germany, the early establishment of a technical standard for green roofs emboldened the construction industry to roll them out with growing confidence; encouraged by planning policies, they now feature on one new building in ten. The UK has been more cautious, feeling the lack of adequate evidence on costs, benefits and techniques, says Stuart Connop at the University of East London’s environmental research group. But he sees this slower start as an opportunity to do it better. To maximise the potential of green roofs, he says, we need to evaluate different designs and techniques whose suitability will vary with circumstances, rather than just applying one standard model in a ‘cookie cutter’ approach. That’s why his university has partnered with local authorities and businesses to transfer knowledge via the Green Roof Experimental Research Facility at Barking Riverside – an area of east London where redevelopment plans envisage green roofs on 40% of the buildings. Several London boroughs and other local authorities now officially back the use of green roofs, which are specifically encouraged by the 2008 London Plan.
UK-wide sharing of expertise in this area should get a fresh boost from the Green Infrastructure Partnership, launched in October 2011 under the new government white paper on the natural environment.
Green roofs are, of course, more expensive than the traditional tiled variety, and likely to remain so for a while yet. But there’s more at stake than natural amenity and biodiversity. Green roofs can be very energy efficient, keeping buildings cool in summer and warm in winter. They help combat urban heat island effects, absorb carbon dioxide and other pollutants, provide good sound insulation and enable the recycling of secondary waste as aggregate. They are even compatible with solar photovoltaic panels: by providing some shade and minor water runoff, the panels could, at least in theory, enhance biodiversity. And the vegetation could even help maximise panel efficiency by keeping them relatively cool – thanks to evapotranspiration – on hot days.
Even more striking are the benefits for water management, which a joint project between Thames Water and the Greater London Authority aims to quantify. London’s need for a ‘super-sewer’ could be much reduced by integrating it with green infrastructure, says Connop. Built-in water storage capacity in green roofs takes pressure off both urban drains and reservoirs and aquifers, and their capacity to absorb rain ‘slows the flow’ greatly during sudden downpours, reducing the flooding associated with the spread of ‘hard catchment’ in urban areas.