Water Conservation - 3: ('Blue' Roofs)

Posted on 9th March, 2010

woodland streamSurface water run-off from roofs presents the eco-designer with some problems – but as we all know – problems provide us with opportunities for improvement. Green roofs are well known solutions to slowing down and reducing the amount of rainfall that eventually finds its way back into our groundwater. There is an alternative to this approach ...

THE BLUE ROOF:              The blue roof avoids the necessity for heavy planting materials as required by the green roof, by simply storing excess rainwater in rooftop gullies, channels or gutters. This water is released using flow control devices and can be used for almost any non-drinkable purpose. It can be released to a stormwater harvesting system for later reuse as well as an infiltration system that recharges groundwater, or released slowly as in the SUDs solutions discussed in previous blogs. The blue roof can therefore reduce the costs of installing a traditional drainage system and can replace – or be used together with a lower-capacity SUDs * system. The ratio of captured/discharged runoff is designed to closely mimic the pre-construction hydrology of the site.

APPLICATIONS:                 The easiest opportunity for using a blue roof occurs in a long, flat roofing style normally seen in commercial development. These roofs typically have wide gutters and a good watertight liner. Blue roofs work especially well in highly urbanized areas where there is less space on the site for stormwater detention or where large, highly impervious areas generate a rapid rate of stormwater runoff that can overwhelm drainage systems and cause flooding.  The blue roof can also be used on domestic buildings if planned in advance – and it can solve the old problem of how to get rainwater back up to a level where it will provide gravitational flow to its end-use system.

IS IT SUITABLE FOR YOUR SITE?        Sustainable building design isn’t about which method is better than the other -- it’s about how we consider all the alternatives in any given situation. There are many projects where a blue roof design could benefit both the environment and the client’s requirements. As always – get professional advice early on in the design stage of your project if you want to consider any unusual or inventive eco-building solutions.


* SUDs - please see previous blogs

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