Soil Matters 4 - Jeff Sorrill - Sheffield Green Roof Centre

Jeff Sorrill has been the Manager of the Sheffield Green Roof Centre since its creation in 2007. Only one of a handful of green roof experts in the UK, Jeff plays a key role in helping to generate a greater understanding of green roof technology in the UK and here, Jeff explains why this is so important.

What are the origins of green roofs?

The origins of green roofs can be traced back many centuries, but their modern incarnation dates back to 1880s Germany when tilted and tarred roofs were covered in sand to prevent fire. Over time, residents reported that the sand-covered roofs had seeded and led to the development of vegetation which in turn attracted wildlife and the growth of native plants in the area. They also helped to retain water and provided additional thermal protection for buildings.

Why do we need them?

There’s a range of reasons and the beauty of green roofs is their adaptability in a variety of circumstances. We can install green roofs as a form of smart water management, to dissipate heat in an urban environment, to improve biodiversity, to improve aesthetics, to insulate a building and to provide communities with green spaces. A green roof could even be expected to deliver against all these elements, and potentially even reduce the overall running costs of a building when installed correctly.

Why are we talking about them now?

The rise of the blue and green agenda (water management and environmental protection) has been a major catalyst for the green roof debate in the UK, especially when faced with impressive green roof infrastructures in countries such as Germany. And because green roofs are sustainable, attractive and benefit both the overall environmental credentials of a building, as well as improving drainage, they’re very appealing for a range of audiences.

What are their practical benefits?

The major benefit available to developers through the installation of a green roof is improved drainage. With Government legislation – such as the Flood and Water Management Bill – targeting better management of water on-site, developers need to be able to demonstrate that their building is reasonably self-sufficient when it comes to rainwater management, and green roofs can help them achieve this. But there are other benefits too, such as reduced heating and cooling costs, which make their installation an even more attractive proposition.

How easy are they to install – can they be fitted to any building?

As long as a green roof is designed in at an early stage, their installation is fairly straightforward and they can also be ‘retrofitted’ to existing buildings with relative ease. Due to their inherent adaptability, green roofs needn’t be demanding or overly complex in order to be effective. If designers and clients do want particularly impressive rooftops, a building will need to be strengthened and designed in such a way to support deeper root growth.

What is the role of BSI PAS 100 compost in green roofs?

It’s very important indeed. 20 to 30 percent of a substrate used in green roofs needs to be organic matter in order to provide the nutrients and minerals necessary to support vegetation growth. BSI PAS 100 compost is ideal because not only is it a rich source of nutrients, it is also quality assured and therefore reliable and consistent.

What other vital ingredients make up a healthy green roof?

The UK is restricted when it comes to materials suitable for inclusion in green roofs. UK soil is usually clay-based and good quality topsoil is difficult and expensive to source, so it makes more sense to mix BSI PAS 100 compost with recycled inert materials – such as misfired brick or crushed stone. The inert material provides a consistent, stable material that can absorb and hold water and the compost provides the nutrients and minerals required for root development.

Where can you see the best examples?

In the UK, London is the best example of blooming rooftops with around 900 currently in place - those in Canary Wharf are particularly impressive. After that, Sheffield is developing a green roof infrastructure rapidly with around 120.

What does the future hold?

Legislation is essential, so the Government’s intervention through the Flood and Water Management Act 2010 will have a considerable impact, but so will best practice examples and industry leaders. We’re aiming to address this gap in the market through the development of a Code of Best Practice for Green Roof Installation, which should help to drive greater awareness and outline the specifications necessary to create high quality green roofs.