TTV Project

Green roofs offer answers to some of the urgent challenges faced by our urban societies, including rising levels of urban runoff caused by climate change and impermeabilization, the rapid loss of biodiversity, and a higher incidence of urban flooding. A green roof solution that is currently attracting much interest is Multifunctional Green Roof Environments (GREs), or green roofs that enable urban farming while also supporting biodiversity and reducing temperatures locally.

Multifunctional GREs often have to employ intensive substrates of a thickness greater than 30 cm to adequately host the variety of plants and crops that make up their environment. Such systems can place considerable loads on load-bearing structures.

A promising alternative enabling lighter GREs involves using prefabricated biochar-based substrates (a by-product of the lumber industry). A second valuable innovation that can be applied to GREs is the ability to reuse drainage water. This step significantly reduces the need to use drinking water for irrigation.

This project aims to assess the technical feasibility of an innovative green roof consisting of vegetable gardens using biochar-based substrates and a rainwater recirculation system. Different versions will be developed and monitored experimentally in the laboratory in order to identify the best-performing configurations in terms of:

-        Quantity and quality of water draining through the substrate (and available for recirculation) as well as the rainwater retention capacity

-        Productive capacity in terms of vegetable biomass and use of drinking water

A prototype will subsequently be installed in a real-world setting (a local residence) to demonstrate the potential of the proposed system.

The companies partnering on the project benefit from being able to showcase themselves in the « ville éponge » or sponge city market promoted by the Swiss Association of Water Protection Professionals and from contributing to « Net Zero Greenhouse Emissions » (a directive of the Swiss Federal Council). Partnering companies also receive valuable technical guidance and support in implementing the system in real-world situations.

By developing a low-cost technical system both in terms of construction and use of drinking water, the project has clear potential to make a positive societal impact. It will also demonstrate the advantages of Multifunctional Green Roof Environments to a broad public, notably their tangible benefits in terms of vegetable biomass production and hydrological regulation.