Rooftop greenhouse, Autonomous University of Barcelona, Spain. Photos: CSTB
How much energy, water and CO2 emissions can be saved thanks to rooftop greenhouses? The advantages of these systems are being analyzed by eleven European partners from five countries, including the CSTB for France, as part of the GROOF project (Interreg North-West Europe program). At the end of a phase analyzing the current situation, the consortium began building four rooftop greenhouses and guiding ten projects in Europe. These will help identify best practices in urban agriculture on rooftops and contribute to the development of techniques to adapt cities to climate change.
Advantages of the installations
Two years of work (2017-2019) were needed to take stock of the rooftop greenhouses currently installed in urban areas in the region of northwest Europe. This review was based on a study of the context and on an analysis of existing rooftop greenhouses, throughout their life cycles.
The review quantified the advantages of rooftop greenhouses, in four areas: technical (construction and buildings), energy and the environment, botanical (range of plants) and economic. It highlighted their advantages:
- using rainwater for the plants;
- reducing CO2 emissions in the construction and use of buildings, and in the distribution of the greenhouse's production;
- using the heat loss of the roof to warm the greenhouse;
- increasing the building's property value.
This review, which obviously varied widely depending on the situation, demonstrated the potential impacts in terms of energy savings and decreasing CO2 emissions, which must be compared with actual conditions.
GROOF's consortium of scientific and technical experts is now seeking to demonstrate the advantages of installing greenhouses on rooftops, through pilot projects.
This involves supervising from start to finish the construction and management of four rooftop greenhouses, in Luxembourg (Bettembourg), Belgium (Liège, Liège Province), Germany (Bürstadt, Hessen) and France (Saint-Denis, Île-de-France). So far, the building permits have been approved. Once the greenhouses have been built and are being used, measurements will be taken for one year. The greenhouses should save 300 tons of CO2 per year by September 2021 (end of the GROOF project) and 2 million tons ten years later.
What's more, the consortium is guiding ten rooftop greenhouse projects (design and construction) in five countries. Through a European call for applications, the projects were selected in September 2019 with the GROOF selection panel, in which CSTB participated. Five of these projects, located in France, are now being coached by the CSTB: Toits Vivants in Arcueil; Jardins Perchés in Tours; Yncrea - Le Palais Rameaux in Lille; Culinea Hortus in Paris and Symbiose in Nantes.
Feedback from the construction of the pilot greenhouses will help identify the most durable, relevant solutions and avoid pitfalls in terms of:
- technical aspects: the load-bearing structure, energy optimization systems, cultivation systems, etc.;
- regulatory aspects: building height (local town planning rules), lighting at night, the safety of people (welcoming the public), health risks, etc.;
- economic aspects (business model).
Through these experiments, the experts are evaluating both the advantages and the potential problems associated with each solution, depending on how the greenhouse is used:
- a production greenhouse for a short supply chain;
- an experimental greenhouse to develop a plant range or to test a flow saving system (water or energy);
- a community greenhouse to bring people together or train people in urban farming practices.
The European partners of the GROOF project are currently writing a Guide to Best Practices scheduled for release by the end of 2020. Intended for all of the stakeholders of the city, construction and agriculture, this guide will provide them with practical assistance to reduce the energy consumption and CO2 emissions of buildings with rooftop greenhouses. It will help them choose durable, well-designed solutions. In practical terms, this guide will feature, for example, recommendations concerning the best technical solutions, the choice of plants, the market rules to be followed and the relevant business models.
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