ACO Building Drainage has released the second volume of its Blue Roof Guide, outlining approaches to on-roof water storage and drainage coordination for architects, engineers and contractors working on multifunctional roofscapes
ACO Building Drainage has published Blue Roof Guide – Volume 2, expanding on its earlier 2024 publication with updated guidance on designing roof systems that temporarily store and manage rainfall at roof level.
The guide focuses on blue and blue-green roof strategies intended to reduce peak stormwater discharge into urban drainage networks while supporting additional functions such as passive irrigation and biodiversity on rooftops.
It follows increasing pressure on drainage infrastructure linked to more frequent intense rainfall events and growing demand for multifunctional urban roof space.
The second volume develops earlier principles of blue roof design and sets out approaches to off-membrane water storage, alongside practical coordination guidance for project teams working across architecture, engineering and landscape disciplines.
It also references the role of blue roofs in combining drainage control with green and biosolar roof systems, allowing vegetation and photovoltaic installations to operate alongside water attenuation measures without compromising waterproofing layers.
Technical content includes detail on the use of the manufacturer’s geocellular attenuation approach through its RoofBloxx system, which is designed to sit independently of waterproofing layers and provide shallow water storage above structural roof decks.
The guide also outlines supporting components used in system design, including flow control devices, access chambers, diffuser units, capillary wicks and reservoir trays. These elements are described in relation to controlling discharge rates, supporting planted roof irrigation and improving system stability.
Neill Robinson-Welsh, technical lead at ACO Building Drainage, said the approach reflects lessons from completed projects and increasing use of blue roofs in dense urban developments. He highlighted the importance of separating water storage from the waterproofing layer and coordinating system components early in the design process.
The publication also addresses early-stage design considerations such as outlet positioning, roof falls, structural loading and the integration of maintenance access. It recommends routine inspection regimes and permanent access provision to support long-term performance.
It also notes the importance of hydraulic calculation during design stages to ensure systems meet local discharge limits while accommodating architectural and servicing constraints.
ACO Building Drainage states that blue roof systems should be treated as integrated design exercises involving multiple disciplines from the outset to reduce the risk of later redesign during construction.
The guide is available via the company’s website.
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