Rotterdam presents potential of the roof

More and more people are coming to Rotterdam. To live, to work or to visit the city. To create a place for all these functions, we have to be smart with our space. One of those places where there is space in the city is right above us. On the roof. The Municipality of Rotterdam commissioned the company Sobolt to investigate the surface area and potential of Rotterdam's roofs.

"Only a relatively small amount of research has been done into what we can do with our roofs," says Paul van Roosmalen. Paul, who works for the Municipality of Rotterdam, has been working with his team on the roof issue for several years. In 2015, De Urbanisten was commissioned by the Municipality of Rotterdam to map out all possible functions for roofs. What started with a Green Roofs Programme has developed into a multifunctional roof programme, with – in addition to green – yellow, red, and blue roofs. The colours represent the functions that are possible on roofs. Green, water, recreation, and sun. And soon there will also be orange roofs. Mobility. There are currently about 80 projects underway that are part of the roof programme.

Rotterdam's roof in the picture

We already have good insight of the possibilities that our roofs offer. But what was still missing was a clear understanding of Rotterdam's existing roof landscape. How many km2 of roof surface does Rotterdam have? What do Rotterdam's roofs look like? For which functions are they suitable? Which roofs have already been  claimed, and where are other opportunities to be found? These are some of the questions the municipality is looking to answer. Paul: "Once we’ve established this, as a local authority we can start developing policies on how we can most effectively use our roofs. That means we can also start steering. To give an example, it makes more sense to opt for green roofs and water storage in an area with  modest green space, such as in Noord. While in a city district where there is already a lot of water, such as Maashaven, solar panels may be the most suitable solution."

Numerous possibilities on the roof

The Municipality of Rotterdam commissioned the company Sobolt to provide information on how many km2 of roof surface there is in Rotterdam and how many m2 are already in use as green roofs. According to Sobolt, this is only a first small step towards the many possibilities. In 2016, initiators Jeroen van Zwieten and Danny Hetharia started the 'Energy Intelligence' company Sobolt in the Spaces office in Rotterdam. Both entrepreneurs shared a passion for renewable energy and making this accessible to all. And not without success: in two years' time, the company grew from two to fourteen employees.

Artifical Intelligence (AI) as a basis

Sobolt combined various data sets to map out Rotterdam's roof landscape. The company obtains unique insights by combining AI, physics, and earth observation. For Rotterdam they combined the Basic Administration of Addresses and Buildings (Dutch BAG), satellite images, and aerial photographs. With this as a starting point, the company taught a computer to recognise roofs and to also recognise the green roofs on them. This is easier said than done. Jeroen: "There were many 'false positives'. These are places that the computer incorrectly designates as a roof or green roof. Moss on a roof, for example. Or a tree hanging over a roof. As a solution to the latter problem, we used a point cloud. With the aid of that cloud we taught the computer to recognise the shape of a tree and to filter it out of the results.

The research revealed, among other things, that Rotterdam, including the port, has 18 km2 of roof surface. Of this, approximately 450,000 m2 is already in use as a green roof. This turns out to be approximately 75,000 m2 more than expected. Until now, the municipality only had an impression of the surface area based on grant applications. The results of the first study are just the tip of the iceberg. Jeroen: "If it's up to us, we'll have Rotterdam's entire roof landscape in view in a year's time. That means that we'll not only be able to say something about the surface area, but also about the shape, bearing capacity, and slope angle". Paul: "And once we know that, we as a local authority can work out  specifically which function fits best where. So there is still a whole world to discover on the roof."

More information?

Questions about the Rotterdam roof programme can be asked to programme manager Paul van Roosmalen. Would you like to know more about the Rotterdam Smart City programme? Then contact Frank Vieveen, Smart City development manager. Visit the Sobolt website to learn more about other energy solutions of this great Rotterdam based company.