CASE STUDY: installing green roofs

Can there be wildlife in our urban jungles? Matilda Lee meets a man campaigning to let nature live on city rooftops

It all started with the black redstart. With only 100 estimated nesting pairs, this bird, a brown and gold relative of the robin, is one of the UK’s rarest species. The bird thrived in the rubble and sparse vegetation of London after the Second World War, as this resembled its natural habitat in the Alpine slopes. In particular, it settled in brownfield sites (vacant or derelict land or buildings) in south-east London.

Dusty Gedge, an actor and circus performer (specialities: juggling, unicycling and tightrope-walking), had been an avid birdwatcher since the age of seven. In 1997, a conservation officer in Deptford, south-east London, recruited him to do a bird watching survey for a creekside regeneration project.

The black redstart is protected under the 1981 Protected Species Act, by which it is an offence to intentionally disturb a bird’s nest-building or caring for eggs or young. At the crack of dawn, Dusty would find himself visiting sites being developed in brownfield regeneration projects, where the bird was known to nest. He’d try to ‘occupy’ the site and stop the building until the birds had finished nesting. This didn’t win him many friends, but it did get attention – from the local council as well as groups such as English Nature and the Environment Agency. The building would be stopped to re-evaluate the site for protected wildlife species, which, in the short run, allowed the birds to finish nesting. But as a long-term solution, it didn’t help the black redstart as there were no plans incorporated to recreate its habitat. That is, until the idea of a green roof came about.

‘The attitude of developers was, green roofs were only meant for hippy community centres,’ says Dusty, a rugged, chain-smoking south Londoner. He heard about a Swiss scientist, Dr Brenneisen, the world authority on the use of green roofs to promote biodiversity, and went to see him. The Swiss had successfully designed rooftops to recreate the black redstart’s natural habitat, combining urban design with specific conservation and biodiversity objectives. In the Swiss model, Dusty discovered that green roofs could mean much more than a hippy hang-out or yuppies’ terraced rooftop garden.

The roofs Dusty promotes may not even be green. Designed to mimic natural and local habitats for the benefit of bird, plant and insect species, they use building construction waste (stone or brick rubble) interspersed with seed mixtures – then leave the rest to nature. These ‘laissez faire’ roofs require little or no input (no watering, no mowing). The first ‘biodiverse’ or ‘brown’ roof that Dusty was instrumental in creating – on the Laban Dance Centre, in Deptford, south-east London – was built specifically to house the black redstart.

Holistic view

Fast-forward 10 years and Dusty, from his own experience and research, has compiled a vast sum of case studies, research and information on green roofs, which is available at the tip of his tongue (and on his website, www., a UK portal run from his kitchen table). From stormwater amelioration to saving the sockeye salmon in Portland, Oregon to green roofs in Germany providing refuge for the skylark, Dusty is a walking encyclopaedia of green roof case histories. While he’s not the only expert in the field, his knowledge and endless enthusiasm has made Dusty a kind of ‘godfather’ of the green roofs community/movement in the UK. He’s handed in the circus tightrope for a full-time schedule of tours, meetings and speaking engagements with everyone from ecologists to government officials, corporate executives, architects and developers. Gary Grant, a consultant ecologist and author of Green Roofs and Facades, says, ‘I think Dusty’s spoken to every local authority in London. He’s a tireless campaigner.’

‘Green roofs were a new discipline for me,’ says Dusty, ‘but my advantage was not to be constrained by the mission statement of one organisation. I didn’t approach it being an architect or in the construction industry – I learned on the hoof.’ His philosophy is very much centred on locality. ‘You want green roofs to mimic the natural landscape. Near rivers, you could have a dry riverbed habitat. In Durham they could have magnesium limestone grass; in Alpine climates you have dry meadow flowers. The more diverse the species, the better.’

But it’s not only the black redstarts who are served: green roofs also offer potential benefits to humans in the UK. ‘With serious downpours, rainwater goes straight from paved roofs into roads, rivers and into sewage systems, contributing to flash floods. A green roof will absorb this heavy rainfall – by 50, 60, even up to 90 per cent, storing it in vegetation until it is absorbed back into the atmosphere,’ Dusty says. With UK flood damage costing hundreds of millions of pounds over the past few summers, and some two million commercial and residential properties at risk, green roofs are a wise flood prevention and mitigation measure.

The urban ‘heat island effect’ is the difference in temperature between urban areas and the surrounding countryside due to the abundance of hard-standing, cement buildings, roofs and pavements, which absorb the sun’s heat rather than reflecting it back into the atmosphere. At the peak of the 2003 summer heatwave, for example, London temperatures were 9°C higher than in the surrounding green belt. This phenomenon will only get worse with climate change. Widespread green roofs would reduce local temperatures and help to keep buildings cool in summer.

Since 2004, Dusty has served as an expert on a panel for green roofs at the London Plan, the Mayor’s planning strategy for London, trying to get the message across about the multiple benefits of green roofs – from biodiversity, stormwater drainage and heat island effect, to reduced energy and therefore co² emissions. All the same, green roofs went from being a ‘requirement’ for every new building of 100 square metres or more, and all major building refurbishments, to a ‘recommendation’.

Now the Greater London Authority (GLA) has commissioned a report, of which Dusty is one of the contributors, to justify why green roofs should be a requirement. ‘For me, it’s a no-brainer, but you can’t tell that to an architect… [There’s] nothing wrong with [Richard] Rogers [head of the Mayor’s Urban Task Force] and co, but they are more interested in designing a roof that people can have coffee on.’

Although green roofs might appear to be in competition with the ‘hard technologies’, as Dusty calls them, of photovoltaic (PV) power and wind farms – ‘solar PVs are sleek and silver and vegetation is weedy and untidy,’ he says – Dusty believes you shouldn’t choose one over the other. ‘In Germany, you have to have green roofs when you have solar PV because it enhances the microclimate for it. The optimal temperature for solar PV should be 25°C. Every 5°C above 25°C, you lose eight per cent efficiency in the PV. Because of evapotranspiration, roof vegetation helps maintain a microclimate of 25°C.’

Big business, big roofs

In September 2004, Dusty was tending a stand at a ‘Green Day’ event at Canary Wharf, to raise awareness of the black redstart. ‘A guy came over and kindly asked what could be done to help. I told him: “Shove a green roof on your building”.’ The following year, with Dusty’s consistent support and prodding against initial reservations at corporate HQ, Barclays Bank built the highest green roof in Europe. Retro-fitting 400 m2 of rooftop area using recycled crushed brick, pre-grown sedum mats and wildflower mix has helped the idea to catch on in one of London’s most built-up areas. At Canary Wharf there are now seven green roofs, including Barclays – representing an estimated 20 to 30 per cent, Dusty calculates, of the total possible area.

‘If you think of every bank or law firm that, no matter why, wants to do something for the environment tomorrow, green roofs offer a diversity of environmental returns,’ says Dusty.

His enthusiasm certainly convinced Tony Partington, managing director of Canary Wharf Management Ltd. Partington has had green roofs made on five of the seven buildings they manage, which has resulted in black redstart nesting areas. ‘I wouldn’t know a black redstart from a crow,’ he adds, ‘but that’s what Dusty tells me.’

Even so, there are also benefits to a company’s bottom line. While there has been no official study on the cost-savings of green roofs in the UK, there is plenty of anecdotal evidence. Burnett Parsons, building manager at 10 South Colonnade, Canary Wharf, says that since their own green roof went up, there has been no need to heat or cool the top floor. Parsons estimates that this has reduced costs in electricity by £4,000 to £5,000 a year.

And Dusty is hot on the trail of more greenable roofs. ‘Croydon, Canary Wharf, Brentford and other commercial nodes – they’re the battleground where I’ll be focusing,’ he says. There is plenty of scope: London’s greenable rooftops comprise an area 10 times the size of Richmond Park. Taking into account flat or gently sloping rooftop areas across all of the UK’s cities offers a potentially green area roughly the size of Manchester.

Nigel Dunnett, a senior lecturer at the University of Sheffield’s Department of Landscape, met Dusty at a Chicago Green Roofs conference in 2000. Together they organised the UK’s first green roofs conference (in 2003), out of which came Sheffield’s Green Roof Forum, which has been instrumental in developing city policy. Sheffield’s Local Plan will require green roofs for all new flat-roof developments – commercial and residential – in the city centre. It is still in draft form, but if it pulls through by next year, it will be a first in the UK.

In the grand scheme of things, Sheffield new-builds might seem small-scale in the efforts to reduce climate change and its impacts and preserve endangered species. But not when you’re someone used to measuring success bird by bird.

For more info

There is a ‘Green Roof Forum’, plus information and resources on green roofs, at Dusty will co-lead domestic-level green roof seminars in June 2007. For details see website. Green Roofs and Facades by Gary Grant (, £22.50)

This article first appeared in the Ecologist May 2007

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