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A discussion about green roofs in the UK always ends up eulogising the many examples in Germany and Switzerland and bemoaning the sad state of the industry here. Why, in this country of gardens and gardeners, haven't green roofs caught on? In Germany over the last decade, the installation of green roofs has grown by 10 to 15 per cent annually, largely because many German cities provide financial incentives.

In the UK there is little policy framework and a fragmented approach to green roofs. Until recently they were found only on high-profile environmental buildings whose mission was to showcase sustainability. But there are encouraging signs that the green-roof landscape may be starting to change.

Bauder and Alumasc, two of the leading suppliers of proprietary green-roof systems in the UK, have seen a significant increase in sales recently. Bauder reports a steady rise, from 23 per cent in 2003, up to 45 per cent in 2005.

Alumasc has seen its sales treble since 2000 and predicts a 40 to 60 per cent growth in the next two years. New products are also entering the UK market, as evidenced by the range of sponsorship for this year's AJ conference.

Living Roofs was established in 2004 as a campaigning organisation to promote and disseminate information about green roofs in the UK. Its excellent website ( www. livingroofs. org) has summaries of the benefits of green roofs, perceived barriers, links to major suppliers and an audit of more than 50 UK examples, as well as numerous case studies. Particularly useful is a section on guidelines for the planning, installation and maintenance of green roofs, largely based on German standards. The Living Roofs annual conference in Sheffield in June attracted over 200 people and next year it will take place in London. Sheffield is in the process of developing a green-roof policy, which will be the first in the UK.

Building on the work of Living Roofs, CIRIA is completing a UK guidance document on green roofs, to be issued in the autumn. The document will be a major step towards overcoming the fact that so much of the available technical literature is in German. It will summarise technical, structural and planning issues related to green roofs, with particular emphasis on how they can contribute to biodiversity, sustainable drainage and thermal efficiency. The CIRIA document is intended to be disseminated through workshops and training.

Visit www. ciria. org/ buildinggreener for details.

The advantages of green roofs are well-documented:

improved insulation; waterretention and reduced drainage;

longer life for the roof membrane; reduced air pollution; increased biodiversity;

and aesthetic value. Less wellknown, but with enormous future potential, is their role in enhancing the efficiency of photovoltaic panels (PVs) by contributing to a more stable temperature at roof level. PVs are temperature dependent, so less efficient if the surrounding ambient temperature is too hot.

Barriers hindering a more widespread use of green roofs include affordability, apprehension and resistance to new technology, and the increased co-ordination required between supplier, contractor and client or end user. The lack of a British standard creates uncertainty and means that many first-time users opt for off-the-shelf proprietary systems from established manufacturers in order to obtain guarantees and to reduce risk - known materials and weights ensure known performances. This cautious approach leads to increased costs. The opposite end of the spectrum, which has more in common with some of the Swiss examples, relies on site-sourced materials. Although perhaps a more sustainable approach, this introduces many unknowns and requires a client who is willing to take a risk.

Alun Tarr of Blackdown Horticultural Consultants, which designs, supplies and installs green roofs, argues for a more integrated approach to design, supply and maintenance.

Tarr explains that the green roof industry in the UK is an extension of the waterproofing industry, which means that contractors, rather than installing inanimate materials and then walking away, are suddenly faced with animate plant materials that they do not understand. 'Common sense [like the fact that waterproofing must be programmed first] goes out of the window, ' says Tarr, because contractors are dealing with new roofing technology.

Tarr insists that one key to success is the clear allocation of contractual responsibilities, particularly determining who is responsible for ensuring that the waterproofing is adequately protected.

The London Borough of Lambeth's Housing Services is pioneering the use of green roofs in the public sector.

For the Ethelred Estate in Kennington, Bauder grew and supplied the sedum roofs for 10 buildings, totalling 4,000m 2. Bauder also provided the waterproofing system.

Installation was carried out by a specialist contractor, trained by Bauder, and work was completed in 2005.

Lambeth Housing Services undertook a 60-year wholelife-cost study which concluded that the green roofs cost 13 per cent more than traditional at roofs, but also that there are significant benefits for residents and the community at large.

Two smaller projects are currently under way in Stockwell and Portland Grove.

At the opposite end of the market, Alumasc business manager Nick Ridout notes that there is a growing demand for intensive green roofs from residential developers, who view roof greening as an amenity that can justify higher sales prices for units overlooking landscaped areas.

Developments in the notfor-profit policy arena at Living Roofs and CIRIA, together with a small but significant movement in the marketplace, indicate that roof greening is gaining credibility in the UK.

More successful home-grown examples are needed to build on this momentum.

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