This is good news for Rentokil, the world's largest supplier of indoor plants. The ill-treated spider plant may have cost pounds 1.99, but Rentokil's contract to supply and maintain the plants at Sheffield's Meadowhall shopping centre is worth pounds 333,000.
Plants are put in buildings as an aesthetic afterthought, and while it has long been suggested that a spot of greenery may be good for you, there have been few attempts to quantify and specify the benefits.
Mike Lothian, Rentokil's research manager for tropical plants, said that on the basis of the data an architect could now, for example, design a row of weeping figs in an open-plan office and know exactly what effect this would have on the acoustics. 'Our data will specify the effects of different types of plants and where they should be located to achieve specific acoustic effects.'
Peter Costa, a building services engineer, has spent the past two years studying the acoustic benefits of indoor plants at South Bank University in London. With Claire Simpson, a Rentokil plant scientist, he has worked out which plants make the best sound barriers and how great the effect is.
Kentia palms, weeping figs, the Madagascan dragon tree and the peace lily all reduce high- frequency noise significantly.
The exact data are yet to be published but reductions of 10 to 20 per cent were recorded. The research showed that these plants are effective because they have lots of small leaves that deflect sound in many directions. Plants with a few large leaves are not as effective.
'At the moment many building designers are not fully considering the benefits of plants when building acoustics are calculated,' Mr Costa said.
The greatest benefits are seen in reception areas and entrance halls where there are lots of hard surfaces, such as glass and marble, which reflect sound rather than absorbing it.
Rentokil is sponsoring another Ph D student at Oxford Brookes University, who has attempted to quantify the psychological benefits often claimed for plants. This work is now being written up, and Mr Lothian says a link between plants and increased productivity has been demonstrated.
Other work has shown that plants reduce the energy requirements of buildings by providing a cooling effect in the summer, reducing the need for mechanical air conditioning.
Further research is about to start in collaboration with the Building Research Establishment to see if plants ameliorate the effects of Sick Building Syndrome. Mr Lothian says the existence of the syndrome, which causes various respiratory and allergic problems in office workers, is now acknowledged, but it is not known if the causes are physical or psychological. Either way, the research will attempt to discover if office plants can reduce its incidence.
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