Green roofs extend the life span of a building, reduce the load on drainage during downpours, increase biodiversity, and have positive effects on human wellbeing. The state and municipalities own many buildings with flat roofs, from schools and kindergartens to sports halls and office buildings. Many facilities are currently subject to energy, fire, or spatial renovation projects, and adapting to climate change and implementation of blue-green infrastructure is becoming a duty, not a choice. So why aren’t there more green roofs in Slovenia and how can Slovenian municipalities change that?

To encourage greening of roofs with good practice, we populated a flat roof at Stane Žagar Primary School in Kranj with greenery and showed the potential that accessible green roofs bring to the building and the city. In addition, we prepared an inventory of flat roofs for the City Municipality of Kranj in municipal or public ownership, which will serve as a basis for the preparation of renovation projects and strategic greening of city roofs.

Green outdoor classroom

The green roof at Stane Žagar Primary School functions as a classroom and an outdoor garden. With the greening of one flat roof, the school gained 360 m2 of additional usable space, two outdoor classrooms, and the possibility of having outdoor lessons. 250 m2 of the roof are planted with various types of greenery, of which 150 m2 with extensive landscaping, 70 m2 with perennials and herbs, and 30 m2 are occupied by flower troughs with edible plants (raspberries, blackberries, grapes, and strawberries). The rest of the space is reserved for outdoor classrooms equipped with desks and benches.

The roof bearing is strong enough to accommodate two classes at a time. It is designed to be easily maintainable and to promote pupil participation in the care of the greenery. The children also take care of the troughs with edible plants.

Effect: rainfall retention and user wellbeing

Special layers in the green roof of the Stane Žagar primary school retain up to 80% of the water during heavy rains, and the retained water serves as a reserve for plants on the roof for the dry season. During the summer the vegetation protects the building from the sun and lowers temperatures on the roof and inside the building. Rainwater is also collected on the roof for additional watering of edible plants. Even more important is the impact of the green roof on the wellbeing of teachers and children, the main users of the roof. The roof has become a new common open space that allows access to fresh air, contact with plants and new learning opportunities. It is always visible from the largest classroom in the school, where music lessons and school performances take place.

Mapping flat roofs for strategic greening of city roofs

We prepared a detailed mapping and calculation of the greening potential for 12 buildings with flat roofs in the Municipality of Kranj. We included key data needed to select a green roof and to choose the type of landscaping: roof area, slope, existing accesses, visual exposure of the roof, shading, roof construction, final layer, and the possibility of additional loads. The catalogue can be used by the municipality to prepare the next roof greening projects and to make strategic decisions about future measures. As part of the pilot landscaping, municipal employees gained concrete experience with the installation of green roofs, while school principals and other decision-makers developed a positive attitude and enthusiasm for green roofs.

Catalogue: Green roofs in Kranj (only in Slovene)