Dusty Gedge, the president of the European Federation of Green Roof Associations, made the comments following the release of the draft London Sustainable Drainage Action Plan on 29 October.
The plan highlights how London properties can be retrofitted with sustainable urban drainage systems (SUDS) measures such as green roofs, with an aim of making a 25 per cent cut in surface water flooding across the city by 2040. Thames Water also announced its "20for20" programme, a £20m grant to be used on green infrastructure/sustainable drainage projects over the next five years.
Green roofing is a £20m per year industry in the UK and those in the industry are highly knowledgeable, said Gedge. Trade bodies such as GRO and BALI, with codes of practice, ensure high standards are maintained, and their innovations have helped make London "one of the green roof capitals of the world".
But their expertise will be wasted if consultancy firms are given the lead, and the horticulture experts that have led the way on green roofing and other SUDS measures are not invited to the table, Gedge warned. "We have a lot of knowledgeable people within the industry. They have that knowledge - but will they be talked to? That's always the problem," he said.
"I can see this could go several ways - potentially with a lot of money being wasted on consultation and professional fees and less on implementation. How much is going to be spent on employing people to decide whether an intervention should happen - whether that's a rain garden, a green wall, a green roof?"
Another risk of the engineering consultancy approach is that Thames Water could prioritise the number of litres of water stored at the expense of the biodiversity and beauty that green roofs, walls and rain gardens can provide.
"We want good, resilient, sustainable green roofs that work for 50-100 years - and they need to look good. But once it becomes engineer-driven, we start looking at the numbers and lose sight of the physical, visual practicalities of green roofs. They all think it's about storm water and no one cares about the plants - but the better the vegetation, the better the storage."