This FPX Talk took place december 2, 2020 

Digital green roofs

Sustainable infrastructure that reduces operating costs and improves energy efficiency, stormwater management and biodiversity is becoming more and more of a reality. Green roofs can have those very functions if they are located in the right place. With all the available data today, it is possible to calculate how to take maximum advantage of the surrounding environment and harness its synergies.

Olivier Rostang is writing his Master’s thesis on Digital Green Roofs at the Swedish University of Agricultural Sciences (SLU). We heard him talk about how to find the optimal places to build green roofs using GIS, with examples from Uppsala in Sweden.

Identify optimal areas for green roofs using digital methods
Green roofs are an extremely exciting area of research and lots of research teams around the world are working on improving the technology. An important aspect when talking about green roofs is where they should be placed.

Green roofs are not a new technology per se. They can be traced back to Viking settlements where they were used for insulation. Today, green roofs are once again generating great interest, largely due to ever growing environmental requirements. Through initiatives such as the UN’s Sustainable Development Goals and the European Green Deal, we see that environmental requirements and demands for circularity will affect how people think about the design of cities in the future to an even greater degree.
At the same time, our compressed and expensive cities have plenty of space on rooftops which are not used for anything else. Many cities around the world have today begun to require new buildings to include green roofs for example. Innovation linked to the environment and health is also increasingly valued, and digitalization is taking a higher place in almost all industries.

One Roof – Five Possibilities
In collaboration with Anthesis, FPX has – through a project called One Roof – Five Possibilities – developed and calculated the economic effects of five different types of green roofs: a water roof, an energy roof, a biodiversity roof, a recreation roof and a food roof. Based on this project, Olivier Rostang has looked at the ecosystem services that each roof types provides and used GIS to model synergy effects and find the best location for each roof. An example of the approach is demonstrated through the water roof.

Where is the best location for a water roof, based on the ecosystem services it provides?
Olivier has started from the district Sydöstra staden in Uppsala where over 20,000 homes and 10-15,000 workplaces are planned, as well as a new train station towards Stockholm. Innovation and sustainability have a central place in the urban development project.

The water roof provides ecosystem services in the form of high biodiversity and pollination services, good noise reduction and, above all, stormwater management. Identifying where these ecosystem services may be needed services as the main rationale of the thesis. By looking at these three main ecosystem services for a water roof, he has developed three sub-models:

  1. Noise Pollution Risk

The water roof provides noise reduction – and should therefore be placed in a location that is exposed to higher than average levels of noise. This is done by ranking loud areas at the top of a suitability scale and reducing the score on this scale by the distance to the sound source. By looking at where there will be railways, public transport, roads and how loud these flows are, one can thus get a GIS map that shows which areas may be exposed to noise.

2.Cloudburst risk

A major risk for cities today is heavy rainfall in short periods of time. An example is Copenhagen in 2011 where it rained 150 mm in two hours, which led to major floods which dealt around SEK 10 billion in damages. Since the water roof’s main task is handling stormwater, it is interesting to look at where that ecosystem service may be needed. By using a topographical elevation map, one can identify which areas consist of sinks or pits and which may be filled with water when heavy rainfall hits. By combining this information with a map that contains buildings, it is possible to visualize and identify which properties are located in exposed areas. This allows to calculate not only which buildings are in the danger zone, but also how much of the building is in the risk zone and how quickly the sinks can be filled with water and therefore which buildings should be equipped with a water roof.


This model can be further developed, to incorporate more data which will make it more accurate but also to provide economic estimates of how much money can be saved by using different types of roof.

Olivier has also begun the work of looking at the Energy Roof. There he has recreated the buildings in 3D with height indications to be able to determine how much sun a roof can get, for example if they shade each other. There one can clearly see which roofs are best suited for solar panels and which roofs should be used for something else.


Other green roof projects

There are other projects that work with exploring and developing green roofs, including one team in Paris where the focus is on biodiversity roofs and to determine how biodiversity really works on green roofs and in cities. Olivier also points to an interesting Swedish project, the BIG project in Gävle, Sweden, where FPX participates. It examines how to mix even more criteria such as personal and social health, ecological resilience and the connection between man and nature.



Sydöstra staden in Uppsala has the potential to become one of the first cities in the world with an extensive range of green roofs. This could be an ideal place to study the interactions of people and nature in the city. However, more work is needed to explore how a market-driven development of green roofs could take place. An important conclusion that Olivier has drawn from his sustainability studies is that if you want to create resilience, you should not build the same thing everywhere, and therefore that diversity and redundancy are decisive factors in anything we do.

What is GIS?

Geographic Information Systems are systems for collecting, managing, analyzing and visualizing information associated with a place. GIS provides a good basis for decision-making when the geographical location is important. With GIS, you can get answers to questions about where, where or from where. You can also analyze and interpret large amounts of data and visualize complex information in a clear way. This makes it easy to see patterns and trends. GIS simply contributes to better decision-making for all and a more efficient society.

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