The London Plan makes improving the ‘liveability’ of the capital a top priority. Both the mayor and his chief advisor on architecture and urbanism, Richard Rogers, see green roofs as a key element in achieving this goal. Green roofs meet a number of the mayor’s aims for improving the city – they improve the environment, encourage biodiversity and help to attract a wider range of people (such as families with children, young couples and older residents) to urban living. They create pleasant spaces that soften the urban landscape and help address a basic human need for contact with nature. Simple things like seeing seasonal changes can significantly reduce stress.

Roof gardens promote physical wellbeing too, because plants naturally absorb carbon dioxide and produce oxygen. They also trap airborne particles, including heavy metals like lead. Then there’s the natural insulation, which reduces heat loss. On average, a green roof keeps a property about five degrees warmer than a normal roof. However, during hot weather, a green roof keeps a property cool, as natural plant and soil processes reduce the amount of solar energy absorbed by the roof membrane. A survey by Nottingham Trent University found that when the mean external temperature was 18.4 degrees Celsius, the temperature beneath a green roof was 17.1 degrees, compared to 32 degrees under a normal roof. Applied across a whole city, temperature benefits like this have major implications.

A recent study in Chicago estimated that $100 million could be saved every year in heating and air conditioning bills if all roofs in the city were “greened”. And, of course, green roofs require no extra space -particularly useful in London where land is at a premium. In fact, Ken Livingstone described the capital’s rooftops as its “most under-used asset”. But why is London so far behind? Germany, the world leader in green roofs, is light years ahead by comparison. According to the UK’s only independent promoter of green roofs, Livingroofs.org, there are 13 million green roofs in Germany and their production is a £150 million-plus industry. By contrast, the UK green roof industry is worth just £10 million. For Livingroofs.org director, Dusty Gedge. there are a number of obstacles to negotiate before we catch up. “There are three main problems,” he says. “Firstly, there are no incentives for developers. Second, generally speaking, there is a conservative mindset in the construction industry that resists new ideas.
“And finally, there is a problem with the way the cost of green roofs are calculated.

A green roof retains around 80 per cent of the rainwater that falls on it, saving on drainage, but a QS doesn’t consider this when they price it up. So PFI projects, for example, don’t have green roofs because they’re ‘too expensive’, even though in the long-term they pay for themselves. “All of the problems Gedge identifies can be tied together by a common strand – a lack of understanding about green roofs.

“A lot of planning authorities, architects and developers don’t understand. A councillor on a planning committee told me he doesn’t want green roofs because he thinks they need a combined harvester! “Even if councils specify a ‘green roof for a building, the description is so loose that you could literally paint the roof green and still meet the requirement. We need detailed stipulations for green roofs that outline what they should achieve, be it public space, nature conservation or visual amelioration.” Gedge also believes that the UK, like other countries, should offer incentives to develop green roofs. “In Germany, tax rebates are available to ‘minded’ to approve green roofs. They can’t actually demand them and enforce that demand. However, huge sites in Battersea, the Greenwich Peninsula and King’s Cross will have some green roofs through the use of planning conditions relating to protected species.

Many other such sites exist in London and they should be covered with green roofs.” For Gedge, the time has come for the mayor to back up his positive talk with concrete action. “The people at the top need to take this seriously,” he says. “The GLA needs a green roofs taskforce to look at the real issues. Green roofs are not just for people to “A councillor on a planning committee told me he doesn’t want green roofs because he thinks they need a combined harvester! “Developers who build green roofs near the Rhine because they retain storm water and reduce flooding.” he says. “That would be difficult to apply here because the Government doesn’t run the water infrastructure -but we could reward recycling. “Many green roofs use crushed brick in their base, so if a developer recycled a certain percentage, they could get a reduced charge for the removal of the rest or receive a rebate for having less site traffic.

“Other options could be to fast-track planning applications that include green roofs, or to adopt an idea from Chicago, where including a green roof guarantees an extra two storeys. Whatever incentives are used, developers must be convinced of the financial benefits of producing green roofs and authorities must be serious about getting them delivered. “At the moment, in the main authorities are only sit and drink coffee, they reduce C02 emissions, promote biodiversity and reduce the risk of flooding. We’re talking about pollution and climate change here, the issues affect everybody, and green roofs can have a positive effect on them. “Gedge is confident, however, that the tide is turning and that London, and indeed the country, is waking up to the benefits of gardens in the sky. “In five years, I think there will be a national policy on green roofs,” he says,

“The Government’s commitment to sustainability is starting to filter through and once people see the benefits of green roofs, they’ll catch on in London and elsewhere”. In the meantime. Gedge and others will continue to bang the drum for green roofs as riot just a haven from stress, but as genuine contributors to a better environment, o better quality of life and a better city.