Green roofs go back thousands of years – now modern vegetated roofs can save energy

GOING GREEN means more than just talk for Maureen Connelly, director of the Centre for Architectural Ecology in Vancouver, Canada. She’s a passionate advocate of “vegetated roofs” and sees no reason why all flat roofs shouldn’t be covered in a carpet of sedums or fescue grasses to bring them alive.

“We’ve had green roofs for thousands of years, going back to the ziggurats or Hanging Gardens of Babylon,” she says. “In Germany now, one in four roofs are vegetated – simply green, not for aesthetics, patios or beer gardens -– and cities such as Stuttgart offer financial incentives for green roofs.”

Ireland has its own tradition of green roofs, going back to the pre-historic burial mounds of Newgrange, Knowth and Dowth in the Boyne Valley. But apart from a few examples of individual houses and roof terraces of apartment buildings, acres of roofspace on office blocks and shopping centres have yet to be greened.

A by-law adopted by the Swiss city of Basle in 2002 requires that all new flat roofs must be green, which Connelly hails as phenomenal. And in Vancouver, “the roof of the Fairmont Hotel provides $30,000 worth of herbs a year for the chefs in its kitchens — with benefits to the community, the city and the globe.”

There are hundreds of green roofs associated with “condo towers” in Vancouver, but these are usually roof gardens that need irrigation, lighting and security. Fifty per cent of all the roofs in Millennium Water, the former athletes’ village for the 2010 Winter Olympics, are also green, in one way or another.

Billed as a “Green Utopia”, Millennium Water is awash with environmental features. Rainwater is collected in underwater cisterns and used for irrigation in the dry season as well as flushing toilets, energy is extracted from sewage and the highly insulated senior citizens’ block produces as much power as it uses.

Not only do green roofs reduce the urban heat island effect that makes cities warmer (mainly due to the density and energy retention of buildings), but they also significantly reduce the “heat stress” of individual buildings, as the painstaking work by Connelly’s dedicated team of enthusiasts has shown.

At their green roof research facility in Vancouver, provided by the British Columbia Institute of Technology (BCIT), they’ve been testing the performance of different roofs over the past eight years; one is a standard flat roof and it’s flanked by a roof covered in sedums and another in grass and fescues.

One day last summer, they recorded a temperature of 53 degrees Celsius on the standard roof, but only 27 degrees on the two green roofs. There was also a reduction of 80 to 85 per cent in the energy flowing through these roofs and, more surprisingly, they also cut the noise level inside the building by half.

Green roofs rely on rainwater for irrigation, although sedums, as “the camels of plants”, can survive without water for dry periods, needing maintenance only three times a year. And because each roof has a “reservoir layer” to hold excess water, they reduce run-off by 30 to 35 per cent – sparing the city’s storm drains.

With a soil depth of 15cm (six in), Connelly believes that even the extensive flat roofs of Walmarts and other big-volume retailers could easily be “greened”. And the cost is minimal — as low as €40 per sq m “by simply tossing the plants out” once the soil layer is in place, according to her deputy, Jonathan Hay.

Connelly and Hay spend a lot of their time running sustainable construction technology courses for building industry professionals, such as architects. “They need 18 hours [tuition] — minimum,” she laughs. It is through these courses that the benefits of opting for vegetated roofs is being spread.

The next big thing will be living walls and green façades, making use of more diverse plant species. That’s been pioneered in Paris, with such outstanding examples as the ethnographical Musée du Quai Branly, designed by Jean Nouvel, or BHV Homme, the trendy department store near Hotel de Ville.

In Copenhagen, more than 5,000 plants from all over Europe have been used in the creation of a green façade for the European Environment Agency (EEA) headquarters on Kongens Nytorv, one of the city’s main squares. Unveiled on May 22nd last, it has become an eye- catching talking point for passers-by.

With planting mimicking a map of Europe, it is Copenhagen’s first “vertical garden” — an extraordinary thing in itself for such an environmentally conscious city – and was mounted on a steel frame designed by young architect Johnanna Rossbach and structural engineer Peter Lund Christiansen.

Intended to show “Europe in Bloom”, it has an automatic watering system to ensure that the plants survive. However, as all the plants are annuals, it won’t last beyond the summer and will then be given to the University of Copenhagen’s botany department, according to EEA executive director Prof Jacqueline McGlade.

Maureen Connelly believes that green roofs and vertical walls have such positive environmental benefits that they should be promoted with the use of financial incentives as well as regulations, as in Toronto, which adopted a by-law in May 2009; it requires green roofs on all new buildings over 2,000sq m.

The new Centre for Interactive Research on Sustainability at the University of British Columbia in Vancouver has been designed by architects Busby Perkins + Will to be a “zero-energy” building that will be “humane, green and smart”. The four-storey timber structure has a green wall that will double as a sunscreen.

The province of British Columbia is gung-ho about the green economy, which could be worth as much as CAD$27 million (€20.6m) by 2020, according to the Globe Foundation of Canada; that includes clean energy, energy efficiency/management, green building, environmental protection, carbon finance/investment, and “green knowledge”.

The Globe study found that BC’s six green sectors contributed $18.3 billion in revenues to the economy in 2008, accounting for nearly 166,000 direct and indirect jobs — equal to 7.2 per cent of total employment in the province — and forecast that this could only increase by pointing towards a lower-carbon future.

Globe, which hosts a huge environmental conference and trade fair in Vancouver every two years, predicted that the biggest opportunities for immediate growth would be in the energy efficiency/management and green building sectors, both of which are closely tied to conservation strategies and the use of clean technologies.

And that’s all music to Maureen Connelly’s ears.