Blue Roofs
What are Blue roofs?
A Blue Roof is designed to attenuate incident rainfall at roof level, and typically has a green roof as the surface finish. Utilising ‘geocells’ above the roofing system to provide a multidirectional free flowing path for water to reach the drainage points on the roof surface, these geocells provide a void that is designed to provide the attenuation capacity for the storm water.
Primarily suitable for zero falls flat roofs Blue Roofs are designed to allow controlled attenuation of rain fall during heavy and storm events as part of a Sustainable Urban Drainage Systems (SuDS) good practise policy, replicating the natural environment or improving the as built environment. A Blue Roof will treat and release the water at a managed and controlled rate directly into the sewers waterways and river systems
Blue Roof can be created at either roof or podium level above the waterproofing membrane in a warm roof application and above the water flow reducing layer (WFRL) in an inverted application, and should attenuate water for no more than a 24 hour period from the end of the maximum designed rainfall event. The discharge rate should be calculated to allow the roof to be half empty of attenuated water in a 12 hour period.
Blue Roof Standards
Currently there are no Regulations & Standards for Blue Roofs but in October 2019 CIRIA achieved the funding they required to begin work on proposal 3084: Guidance on blue roofs – specification and contractor selection. This project will run for 18 months to 2 years and in the meantime information on Blue Roofs can be obtained via the NFRC Technical Guidance Note for the construction and design of Blue Roofs. Roofs and podiums with controlled temporary water attenuation. A copy can be downloaded here.
Fire Performance on Green Roofs
Building Regulations Approved Document B volumes 1 and 2 contain no specific test requirements for green roof constructions. Instead they refer to the DCLG publication Fire Performance of Green Roofs and Walls dated August 2013, download a copy here.
GRO has also produced its own guidance to assist designers minimise fire risk on green roofs, download a copy here.
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