City gardens grow to a whole new level

Up on the roof: Nigel Dunnett, who started up green roofs as public parks on the tops of buildings.
Up on the roof: Nigel Dunnett, who started up green roofs as public parks on the tops of buildings.
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NIGEL Dunnett is standing amid a small wildflower meadow.

To his right is a pond. To his left a series of bushes and birches. There are butterflies, birds and bees buzzing about.

Blooming: A green roof at 15 Napier Street.

Blooming: A green roof at 15 Napier Street.

The unusual thing?

The 48-year-old is five storeys high above the streets of Sheffield city centre on the roof of the old university’s engineering department in Abney Street.

And another unusual thing?

This isn’t actually that unusual at all.

Birds eye view: The garden on the roof of the old university's engineering department.

Birds eye view: The garden on the roof of the old university's engineering department.

“There are about 25 to 30 of these green roofs across Sheffield - more than any other city in the UK outside London,” says Nigel. “They’re all around but most people have no idea. They pass these buildings every day but don’t realise above their heads are these incredible nature reserves sharing our city with us.”

Indeed, these aerial gardens are a top some of our most famous buildings - including The Cube, in Shoreham Street; the Jessop Building in Leavy Greave Road; the Sound Box, in Gell Street; and Sharrow School in Sitwell Road, Sharrow,.

And it is Nigel, more than anyone else, we have to thank for them.

It was five years ago this month he founded Sheffield’s Green Roof Centre, the UK’s only research, demonstration and education body on the subject.

The Sheffield University landscapes professor had become convinced creating flora and fauna havens above our heads would bring huge benefits including flood prevention, improved energy conservation and a happier population.

“I was in Germany in 1999 where new buildings often have to have a green roof as part of their planning permission,” says Nigel who has spent the last four years also working on the planting at London’s Olympic Park. “I started wondering how such a policy might work in the UK where our climate is obviously quite different, and it seemed to me the benefits would be enormous.”

Spurred on by the university, he organised the UK’s first ever Green Roof Conference in 2003, and eventually set up the centre - a collective of volunteer researchers and academics based in Sheffield - in 2006.

The group investigated the best plants for roof top projects (“something relatively low maintenance” says Nigel), the best kind of growing medium (“lightweight and absorbent”) and the best features.

“What you want,” explains Nigel, “is as much wildlife as possible so the best thing is to have different mediums - water in a pond, different kinds of flowers, even a small wooded area of birch.”

They promoted their ideas across the city and country, offered their own expertise to those looking for help, and set up links with Sheffield City Council. The planning department there was particularly interested, in light of the 2007 floods, by external research showing a good green roof would soak up 50 per cent of rainfall in a downpour.

And slowly - like a flowering roof top meadow, perhaps - Nigel watched the number of these high gardens grow.

“There were precisely none in Sheffield in 2006,” he says. “To see so many of them now feels like a real achievement. There’s one in Rotherham too at the Moorgate Crofts Business Centre.”

And for the future?

“The aim is to see the majority of buildings with flat roofs in Sheffield given a green roof make over,” he says. “Developers can be against them because they do add cost to a building but I think the economic, as well as the environmental and social, benefits really do outweigh that.”

Residents often call Sheffield the greenest city in England. And, from high above the streets, it seems this boast has never been more true.

Go green build your own roof garden

Make sure you have a flat roof. Building a garden might be possible on a sloping top but it’s going to take some serious engineering nous.

Get a light soil. Crushed brick or expanded clay is good because it won’t cause your roof to cave in. Ten centimetres of depth is optimum.

Think diversity. A range of plants is better for attracting more wildlife but it should be low maintenance, hardy and good for absorbing of water. Alpines and sedum are recommended.

Add a pond. You’ll need a large roof for this but it will definitely appeal to wildlife - and impress guests.