Author(s): Alejandro Morales Hernandez
Urban rooftops are increasingly seen as spaces that can help transform cities. They can host vegetation, renewable energy systems, water management infrastructure, social activities and mobility functions. Yet information about rooftop characteristics, ownership, urban challenges and policy incentives is often scattered across different sources, which makes these elements difficult to connect.
Image disclosure: The image was generated with OpenAI's DALL·E image model, using a prompt based on the theme of the Rooftop Activation Ontology.
The Rooftop Activation Ontology addresses this by providing a common vocabulary for describing these elements and their relationships. It offers a structured way to represent how rooftops can be activated, which urban challenges they can address, who can be involved, and which incentives can support their transformation. The current published version is 2.2.0.
The ontology was developed by Alejandro Morales Hernandez from the Machine Learning group at ULB and is part of MultiRoofs (https://multiroofs.nweurope.eu/), an Interreg North-West Europe project exploring how underused rooftops can become multifunctional spaces that make cities more resilient, sustainable, and liveable. The project brings together partners from Belgium, France, Germany, Ireland and the Netherlands to address challenges such as climate adaptation, energy transition, biodiversity and housing, and to develop tools that help cities identify and activate rooftop opportunities.
Structure of the Ontology
The ontology classifies rooftops into seven color-coded activation types: blue, green, yellow, red, purple, orange, and grey. Together, these cover water management, vegetation, energy generation, human occupation, mobility, logistics and infrastructure. It also captures the physical and contextual characteristics of buildings, such as construction period, materials, height, location and primary use.
Rooftop activation, however, depends on more than the building itself. The framework, therefore, connects each building to its owner, district, and region, as well as to the urban challenges that activation can help address. Since owners differ in their capacity and motivation to act, the ontology distinguishes owner types such as homeowner associations, housing corporations, landlords and private individuals.
It also describes the incentives that can support implementation, classified by nature, function, funding source, allocation mechanism, obligation attachment and project stage. This makes it possible to link a specific type of rooftop activation to the actors involved and the available support mechanisms.
Associations between activation types, urban challenges, owner types, district types and incentives can each be given a degree between 0 and 1 and defined for a particular region. The same framework can therefore reflect different assessments and priorities from one city to another.
Impact and Reuse
By making these relationships explicit, the ontology allows rooftop activation to be queried and analysed at the urban scale. A rooftop can be described not only by its physical features, but also in relation to its owner, its district, the challenges facing that area and the incentives that could enable intervention. This gives researchers, planners, policymakers and other stakeholders a shared language for working on the transformation of urban rooftops.
The ontology is published under a CC BY 4.0 license and can be imported directly into other datasets and knowledge models, providing a reusable semantic foundation for research and applications.
Learn more here: https://alejandro3500.github.io/Rooftop_activation_ontology/