We’ve all heard of green roofs and the good news is that they are becoming a much more common sight in the UK these days, but how many of us have ever seen or heard of blue roofs?
The green roof uses vegetation planted on to a waterproof membrane, which as well as serving an aesthetic function, also provides a habitat for wildlife, helps absorb CO2, and creates an extra layer of insulation to the fabric of a building – on average 25% of heat loss in buildings occurs through the roof. Green roofs also help to reduce the urban ‘heat island’ effect produced where a high density of buildings is found and, of course, they help to absorb rainwater.
Blue roofs could well be the next step towards alleviating the problems caused by high rainfall. They work by capturing the rainwater on a flat roof and slowly controlling the drainage over a period of time, thus reducing the stress placed on normal drainage systems in periods of heavy rainfall.
The Need For New Thinking
While everybody now agrees that green roofs are a good thing, there is still a certain degree of scepticism about blue roofs. People worry about the potential dangers of a rooftop membrane failing and that by storing the water on the roof you are placing extra stress on a building.
Similar concerns were raised when green roofs were first introduced, but now that they have proven to be unfounded and the advantages have been well documented, we are seeing a huge rise in the number of living roofs.
Obviously roofs need to be constructed in such a way to be able to support the extra weight of stored rainfall, but blue roofs tend to cost less than their green counterparts. They can be incorporated onto existing flat roofs and have been successfully piloted in New York City and are set to play a key part in urban storm water management in the future. Blue roofs can even be designed to harvest rainwater that can then be treated via filtration and purification for re-use resulting in zero run-off from the roof.
As our climate changes and the demands placed on the environment continue to grow we need to develop the technology to combat flooding and improve our understanding of why these events happen and how we can deal with them. Such technologies and solutions may sometimes appear expensive at first glance, but the cost of urban flooding far exceeds any short-term costs involved in the building process.
The concept of the blue roof is not new, but it hasn’t yet received the attention of urban planners and architects in the same way that green roofs have. Perhaps now, in the wake of one of the wettest years on record, that might well start to change.
Fraser Ruthven is the Marketing Associate for London Drainage Facilities, one of London’s leading drainage companies. London Drainage provides a wide range of drainage diagnostic and repair services in and around London.