Blue Roofs – turning urban water on its head.

Written By: European Sales Director, Hydro International

As we enjoy our first taste of summer, 2014’s winter of flooding has all but disappeared from the public consciousness.  At the height of media hype it seemed mainstream journalists left no stone unturned to speculate on new ways to attenuate torrential downpours and mitigate flooding – often to the disdain of engineers!

So, after the tide of speculation has receded, are there any really innovative yet underexploited technologies left standing – ideas that pass the test of achieving integrated urban water management, in new or retrofit, domestic and industrial settings?

One technology that caught my eye during the debate was the blue roof. It seems blindingly obvious: If you are looking for somewhere to attenuate water in a built-up urban environment; try the roof.  Whether on a new or existing building, a suitably load-bearing flat roof can be adapted to provide temporary storage and controlled discharge of rainwater.  It makes sense.  After all flat roofs can already be designed to take the weight of heavy snowfall and can be adapted with modern waterproofing technologies.

To work, blue roofs need a device to hold back the water: a Hydro-Brake Optimum® Flow Control fitted to the downpipe – an engineering design essential missed by the media speculators. In fact, with the unique sizing capabilities of Hydro-Brake Optimum® blue roofs can be precision-engineered to balance storage and discharge rates to make the most of the space available.

It may seem far-fetched, but actually the technology has already been in use for many years. Hydro-Brake® Flow Controls were first used in a blue roof application over 10 years ago for a large shopping mall and are still quietly doing their job today.

In this example, the storage was retrofitted to tackle a flooding problem.  The blue roof storage was designed on three cascading roof levels, controlled by staged discharge using Hydro-Brake® Flow Controls at the base of gutters positioned at one corner of each storage area.

In this case, the objective was simply attenuation.  It’s only another small leap to realise systems could be developed to re-use the rainwater for flushing toilets or for washing vehicles.  Equally, any discharged water need not head for the nearest sewer; it could form part of a managed SuDS system for infiltration on a development or further above-ground features – eg. a lake or pond.

The concept of blue roofs is close to the more commonly-discussed green roofs and the two ideas may work together to combine storage with vegetation to support biodiversity and perhaps create roof garden amenities.

Blue roofs may sound like a leap of faith – but in fact they are a foundation of integrated water management using proven technologies.  Most importantly, as with many simple solutions they use the best of manufacturing and engineering to mimic nature and achieve sustainable outcomes.

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A hybrid of using flat top roofs is also oversizing the guttering system having downpipes having different levels of outflows to activate the storage levels.
Less likely to block and more reliable.
Each downpipe can then be selected in discharge into various means of attenuation, even irrigation systems for plants / home grown crops, or wetlands / ponds etc.

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