Considered no more than a novelty even two years ago, living roofs and walls are fast becoming established in the building mainstream. This has led to an outpouring of new off-the-peg formats. Many of these were showcased at the EcoBuild event in March, where around 90 exhibitors claimed involvement in the sector.
But some growing pains have become apparent. The iconic green wall at Paradise Park Children's Centre in north London, thought to be the first in the capital, has had to be reconfigured and replanted after largely dying from drought last summer.
Jeff Sorrill, manager of the Green Roof Centre at the University of Sheffield, says: "There is significantly less activity this year because last year little was built other than a few small-scale commercial and domestic developments. But clients are still planning for the future and designers are still designing, which after all is the cheap part."
Living surfaces offer so many positives as to make the choice of specifics seem almost irrelevant. But just as a good garden designer will want to know what purpose a client has in mind for a garden, establishing the primary purpose of the surface early on will make defining the specifics easier.
The growing diversity of formats means there is more likely to be a system to suit the particular demands of each site. But clients are more likely to commit to living surfaces if designers and suppliers can clearly meet their requirements. Below are six ways in which these can vary.
- Is the aim to reduce running costs?
As well as providing insulation in winter, green walls and roofs can alleviate heat in summer, according to AECOM Design + Planning director of ecology Gary Grant.
"When the ambient temperature is 30 degsC, the roads and walls can be 46 degsC, the roofs 77 degsC, but the vegetation will still only be 30 degsC, thanks to shade and evaporative cooling. So there's plenty of money to be saved on air conditioning," he explains.
A living roof may also serve to improve the efficiency of adjacent photovoltaic cells. Dr Nick Buck, sustainability consultant at commercial property consultancy Drivers Jonas, says: "Photovoltaic efficiency decreases above 25 degsC, yet a gravel roof can exceed 50 degsC, reducing efficiency by around 12.5 per cent, while an uncovered roof can top 70 degsC, causing a drop of 22.5 per cent."
Other costs savings the client may have in mind from a green roof include extending the roof life. "By covering a traditional roof membrane with a green roof, you extend its life expectancy from around 30 years to 60," says Buck. "The waterworks in Zurich, Switzerland, has one of the oldest green roofs in Europe. It was inspected recently and was found not to need any maintenance."
Living surfaces also reduce drainage costs, meaning not only smaller drainage pipes but also, in a proposal currently being enforced in Germany, lower bills. Buck says: "Because it produces less run-off, it can serve as a component of sustainable drainage systems."
Already in Germany, fire insurance premiums are lower on buildings with green roofs and walls, which lower fire risk, he says, adding. "UK insurers may recognise this soon." Boosting the building's future value by avoiding onerous legislation later on and reducing the risk of flooding are other ways to make the financial case for living surfaces.
- Does the client want to be "seen to be green"?
"Developers are being canny," says Sorrill. "They're getting something that's cheaper to run and has environmental benefits. They let more quickly and sell better - that's the experience in Sheffield."
As well as economic benefits, living surfaces can do wonders for a client's image. On One Churchill Place, the "Barclay's Tower" at Canary Wharf, he points out: "Putting in a green roof on top of a 35-storey building is one way of establishing your green credentials."
Developers and architects face a conundrum here though in that green walls are far more publicly visible than living roofs. But Sorrill says: "Green walls are not so good from the sustainability point of view because of the amount of water they need."
- Are there planning requirements?
Two things that have ensured the rise of living surfaces on the continent, but have so far been largely absent in the UK, are planning obligations and financial incentives. Buck complains: "At all levels the references (in planning documents) to green roofs are scarce and vague."
Sorrill agrees. "Planners are not as proactive as they might be," he says. "Some cities have supplementary planning guidance, such as the London Plan, which says green roofs are expected on new developments. Here in Sheffield, from next year you will be required to include 80 per cent vegetative cover on a base to a depth of 80mm on any building over 1,000sq m or development of more than 10 dwellings."
"There's huge under-capacity in our drainage system. In maybe seven years, you are likely to have to manage water on site. That's not difficult in the country, where you can just put in a tank. But in a city, where there isn't room underground, 'closer to source' basically means green roofs."
- Is the aim to increase biodiversity?
Sorrill says forward-thinking local authorities also aim to increase biodiversity. "If you are serious about doing that in cities, then this is one way to go about it."
Better known as a lawn and sports turf supplier, Lindum Turf has worked with Sorrill's University of Sheffield Green Roof Centre colleague Nigel Dunnett to develop a turf mat to provide an instant species-rich habitat for green roofs.
Lindum's Wildflower Meadow Mat comes in pre-established rolls, made up in equal parts of wild flowers and meadow grasses grown on felt made from recycled textiles, which also acts as a weed barrier. Managing director Stephen Fell says: "With Sedum alone, you only get three or four weeks' flowering. But this will flower from April to September."
Aldingbourne Nurseries sales coordinator Joel Nash says of the company's modular Living Wall System: "It attracts bees and even spiders into the city." He explains that the system improves a building's BRE Environmental Assessment Method (BREEAM) rating, seen as an objective measure of its environmental performance.
- How important is visual amenity?
When Aldingbourne supplied green roof modules to west London's Westfield shopping centre, visual interest was also important in a high-profile, heavily used site. "We work closely with the clients, using things like bulbs to get an interesting wall all year round," says Nash.
However, European Federation of Green Roof Associations president Dusty Gedge is a fan of more naturalistic "brown roofs" and even "brown walls", which need no irrigation, blooming and dying back according to the seasons and weather.
But he admits: "In an urban environment especially, people expect plants to be green and flowering all the time." He even advises designers, half-jokingly: "Don't work with horticulturists - they want too much."
- Will it be publicly accessible and even productive?
The opportunity for the public to interact with living surfaces was not placed highly among concerns in the first wave of green roof and green wall designs. But with companies striving to be seen as considerate employers, these can provide an extra way to make workplaces pleasant and fun.
Even at One Churchill Place, Barclay's staff are reportedly so keen to weed and water the green roof - hardly a thing of beauty - that competitions are held to select lucky winners to do the work.
Grant points out that roofs can even be used for growing food, but he adds: "You need access and a water supply - it's more like a roof garden and the amount of food you could get is limited. You won't make money out of it." Even walls can be used productively, he says. "In schools, each child can have a module of a living wall in which to grow things like lettuces."
Indeed, Nash says Aldingbourne is "really pushing schools" with its modular walling system - as is Lindum Turf. "It can be an educational tool - the children can monitor them," explains Fell, adding that this is already happening at Sharrow Primary School in Sheffield.
Buck says roofs could even be used for growing short rotation coppice as a biofuel. "Perhaps it's an option for industrial buildings in the future," he suggests. "It's a little far-fetched at the moment."