If you want to find a green roof that really excites passion and inspires people to love the idea of green roofing, my advice is head to Sharrow School in Sheffield. This is one of the most famous green roofs in the country, made by volunteers under the guidance of University of Sheffield expert Jeff Sorrill, and the crowning glory of a highly sustainable primary school. In an area where few local residents get to venture out into the beautiful surrounding peak district, many wild seeds are blown down the valley on the wind and find a resting place on Sharrow School, bringing nature back into the city.
In 2009, two years after its creation, Sharrow was the first roof in the UK, and probably the world, to be declared a Local Nature Reserve. With the great benefits to the environment, school children and local residents no wonder biodiverse roofs are gaining momentum in the UK, possibly set to break the stranglehold of sedum matting on the industry.
So how does one create such a great natural haven? Many brown roofs have been attempted up and down the country, and a few of these which have been targeted towards the protection of brownfield habitats for creatures such as the black redstart have been quite successful, but many have seemed to flop. Did you know that the ICC and other public buildings in central Birmingham have brown roofs? They certainly haven’t made the headlines or generated as much interest as Sharrow, and were primarily focused on research. But what makes the difference between a weedy, ugly patch of rubble and a natural roof top wilderness that sets pulses racing?
Well the location just down the wind tunnel from the peaks has clearly helped Sharrow, and not everyone can call up pioneering national experts to lend a hand. But learning from past successes and failures, here are a few tips that should help.
- Put structural planting in to start. Even Sharrow started with some plants that provided structure and protection for the visiting plants and seed sown neighbours. Many plants will self-seed and spread further onto your roof if you design the substrate to encourage them.
- If you are trying to blend in with or recreate a local wild landscape, look for appropriate species (frost hardy and drought tolerant) and have them pre-grown to add to your roof planting.
- Good germinators can be sown directly onto the roof and will grow over time, but do not expect all varieties to get going. University experts like Nigel Dunnett have come up with great seed mixes of around 30 varieties with the expectation that around half of them should do well on any roof – but you never know which half!
- Don’t think that a wild natural roof doesn’t need any maintenance. The drains will still need checking, and Sharrow School had acquired some cheeky fruit trees and willows that were starting to sprout up among more welcome neighbours. If these were not spotted and removed then nature’s influence would eventually get out of control.
As with any green roof design, it is essential to take into account the location of the building and the needs of the users, in order to achieve a roof that becomes part of your local landscape or cityscape and is truly appreciated.