With the increasingly volatile weather patterns across the globe, but more specifically in Africa, blue roofs offer an excellent water attenuation and management system.

A blue roof is a management system where rainwater is retained and drainage is controlled. This is a great method of water attenuation and the management of stormwater; and can be key to sustainability in buildings.

Flooding is becoming a more frequent occurrence, but a blue roof can ease the strain on waterways, assisting in flood prevention and helping you to reach sustainability targets.

What is a blue roof then?

A blue roof is a system of detention ponds that collects rain/stormwater, temporarily stores it and then releases it slowly when the rain has stopped.

Traditional drainpipes and guttering cannot cope with heavy rainfall, and the sewer systems and waterways end up taking the brunt of it.

A blue roof system stores the water and by releasing it bit by bit, it eases the pressure on sewer systems and natural watercourses and reduces the chances of flooding dramatically. The flat roof is designed to allow controlled attenuation of rainfall during heavy and storm events as part of a sustainable urban drainage system (SUDS), replicating the natural environment or improving the as-built environment.

Blue roofs are designed with numerous drainage and filtration layers. When rainfall lands, the built-up system ensures water slowly drains through the inbuilt drainage system, significantly slowing the movement of water and controlling its discharge. Depending on the design, a blue roof will either treat the water and store it for alternative use, or control a slow release of water into sewers, waterways and rivers.

Rainwater attenuation system suppliers are becoming more common, as the regularity of these flash floods increases.

The difference between green and blue roofs: more than just colour

Green roofs, which sport a layer of vegetation, influence the urban environment and the energy efficiency of a building, while a blue roof system is all about the management of stormwater. Heavy rainfall can have a severe effect on urban sewage systems and low-lying areas, where the polluted water runs into lakes and rivers.

In short, a blue-roof system can be compared to a sponge collecting rainwater in catchment ponds, where it is stored temporarily and is slowly released once the storm is over.

Advantageous and necessary system

It can almost be seen as a form of green infrastructure. Blue roofs are a big advantage in commercial and industrial areas, as it makes up quite a percentage of commercial land in cities. With water that has nowhere to go because of hard surfaces, there is many runoffs and a chance of flooding.

Water damage is a leading cause of property claims, and therefore it can become a necessity and a sustainable solution to environmental challenges as the infrastructure simply isn’t designed to withstand extreme water conditions. If there is water faster than designed for the area it fills up, it backs up and causes flooding.

Advantages of a blue roof system

There are numerous benefits of a blue-roof system, including the management of rainwater during and after severe rainfall. In urban developments, the water often has nowhere to infiltrate or be absorbed into the ground – causing cities, informal settlements and sewers to flood and overflow.

Blue roofs reduce the load of heavy rainfall, preventing the overflow from often very old municipal sewage and storm systems from entering rivers, streams and coastal waters. It eases the pressure on drainage and natural water systems and enables improved flood management opportunities. Blue roofs allow you to move water storage from the ground level to your roof, saving you land square meterage as well as opening new opportunities to help you hit sustainability targets.

Combining a blue roof with light-coloured roofing material reduces the cooling costs of the building. The harvesting of rainwater can be used for numerous other purposes. Some systems can even spray the stored water back onto the roof in a controlled manner to provide more cooling.

Blue-roof systems can also be used in low-rainfall regions, where drought is a problem as the roof acts as a water conservation tool that harvests the water on the surface of the roof and captures it at a controlled rate. This eases the stress on the water supply.

Blue roof construction

A blue roof system is based on a watertight flat roof but instead of the water settling on the surface, it drains through multiple layers which control and regulate the speed at which it is distributed down drainpipes. The top layer may be artificial grass or look like the surface of an all-weather football pitch, but that surface is designed to be porous.

The rainwater seeps through this top layer into an inbuilt drainage and filtration system, which slows down the flow of the water. Once the water has filtered through each level, it is sent to the drainpipe. The speed at which the water is dispersed, is now much more manageable for the sewers to cope with and the risk of flooding is vastly reduced.


The materials used in a blue-roof top are SUDS compliant. The SUDS is a standard that new materials must conform to where drainage is required. They will usually have some form of resin surface with a porous base, which means that any surface water will filter through the top layer and disperse in a controlled manner through the bottom.

Any roofing starts with the original high-quality roof blanket to ensure the whole system is durable. Professional roofing installers who are experts when it comes to eco-specification designs will know the correct materials to use. Refurbishment of an existing flat roofing system might be a great place to start if you are considering installing a blue roof, but it is best to contact a blue-roof drainage supplier to ensure that your roof is suitable.

Click here to watch ACO Technologies’ new animation and learn more about the patented ACO Blue Roof Attenuation system: https://youtu.be/lh4wa3FlG1o

Pros of blue roofs

  • Flood prevention: The ability to control sewer overflow and stop potential disasters.
  • Temperature control: A blue roof can keep a building cool, reducing heating costs.
  • Cost-effective: Cheaper than green roofs and most other forms of flat roofs.
  • Recycling: The water is collected on the roofing and can be used for water features and fountains.
  • Low maintenance: Little to no maintenance is required, as they are self-sustaining.

Cons of blue roofs

  • Leaks: If the roof is not 100% watertight, it can leak and cause damage.
  • Heavy load: A large body of water is heavy, so ensure that the building can handle this extra loadbearing weight. Reinforcement may be costly.
  • Standing water: It can attract insects and specifically mosquitoes.

Full acknowledgement and thanks go to https://www.phpsd.com/, https://www.bmigroup.com/ and https://www.roofingsystems.org.uk/ for the information in this editorial.

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