Blue-Green Roofs: When Building Design Takes Climate Change into Account

Green roofs have already found their place in Czech cities. They bring greenery to built-up areas, improve air quality, and help cool urban microclimates. They are becoming not only an aesthetic but also a functional element of new construction. Their benefits are supported by numerous grant programs, such as the New Green Savings program or municipal grants. The result is an ever-increasing area of implemented projects.

However, in times of increasingly frequent extremes, mere greenery is no longer sufficient. This is where a new generation of roofs, referred to as blue-green roofs, comes into play. They not only maintain vegetative areas but also serve as an effective rainwater management system. They capture precipitation, accumulate water, and allow for its targeted use, for example, for irrigation or cooling buildings. This significantly reduces pressure on sewage systems and helps mitigate the impact of heavy rains.

PolderRoof: a smart solution for smart cities

At the forefront of this innovation is the PolderRoof system from Wavin, which allows the use of flat roofs – accounting for up to 30% of urban areas – as effective retention tanks. "The key is a combination of low, lightweight accumulation boxes made from recycled plastic with smart technologies such as rain sensors, sensors, and weather radars," explains Lukáš Mejzlík, product manager at Wavin Czechia, adding: "The system automatically evaluates the current need, i.e., whether and when to retain, use, or release water, entirely without user intervention."

In addition to automatic control, it offers an online platform that provides an overview of water management and allows for remote parameter settings. This technologically advanced roof type can capture up to 90% of rainwater, which is three times more than a typical green roof, which can only capture around 30%. This makes it an ideal solution for cities looking to improve their water balance, support vegetation, and enhance the comfort of their residents.

Benefits for climate, residents, and properties

An important benefit of blue-green roofs is that they contribute to reducing temperatures in cities. The water contained in the substrate and vegetation helps with natural evaporation, cooling the immediate surroundings and the building itself. The result is a healthier microclimate, lower energy demand for cooling interiors, and better quality of life for residents. Moreover, experiences from abroad show that properties with this type of roof are more attractive to investors, increasing their market value.

"When designing a blue-green roof, proper sizing of the retention part is crucial. Unlike the sewage system, which deals with flow rates, here we are dealing with water volume, the so-called critical rainfall volume," points out Lukáš Mejzlík from Wavin. According to statistics from the Czech Hydrometeorological Institute, the roof should accommodate not only standard precipitation (which accounts for 65-80% of the total) but also help manage heavy (19-34%) or extreme rainfall (1-5%), thus reducing the load on urban sewage and the risk of flooding.

The future of our cities is blue-green

Blue-green roofs thus represent one of the most effective tools of so-called blue-green infrastructure, which is becoming a necessity in adapting cities to climate change. "The Wavin PolderRoof system can be installed not only in new projects but also on existing flat roofs, though it is always necessary to check the building's structure and consult the solution with a structural engineer," warns Lukáš Mejzlík.

The future of cities should be green or rather blue-green, since greenery needs water to thrive. Cities that utilize the potential of flat roofs can retain and smartly manage rainwater use, combat heat islands, and simultaneously offer their residents a more pleasant and healthier environment. Technologies like PolderRoof allow us to realize this vision today. Climate changes are happening and becoming increasingly evident. The good news is that we have the tools to mitigate their impacts. One of them – blue-green roofs – can work quietly, efficiently, and sustainably right above our heads. It would be a shame not to take advantage of it.

https://promo.wavin.com/cs-cz/polderroof