Energetic Performance of a Green Roof in the Tropical Environment of La Reunion Island (indian Ocean)

The green roof technology provides environmental benefits by protecting the base roof membrane of buildings against solar radiation and temperature fluctuations and by helping to reduce building’s energy consumption by direct shading. Although several investigations have been performed to explore the energy performance of vegetated roofs as natural cooling devices, there is a lack of data concerning the green roof potential in the southern hemisphere. The aim of our work was to evaluate for the first time the performance of a green roof in La Reunion Island (Indian Ocean) influenced by a tropical humid climate. A green roof based on three kinds of vegetation, namely Plectranthus neochilus, Kalanchoe longiflora and Sedum reflexum species was compared to a reference bituminous roof during the summer season. The green roof performance was explored by evaluating its effect on temperature fluctuations and heat fluxes. The results showed that the presence of plants led to a decrease in temperature reaching 6.7±0.1°C under the green roof. Each plant also contributed to a low heat flux exchange through the green roof. Indeed, Sedum presented an average heat flux exchange of 1.4±0.3% as compared to Plectranthus (2.3±0.2%) and Kalanchoe (2.2±0.4%). Moreover, Sedum also led to a higher restitution of heat gain (63%) than Plectranthus (54%) and Kalanchoe (51%). Finally, the determination of major parameters including U-value, R-value and k-value, demonstrated the thermal and energetic behavior of the green roof and helped to show Sedum properties for a green roof based in the tropical environment of La Reunion Island. To conclude, this study has evaluated for the first time the thermal and energetic performance of a green roof in an Indian Ocean area. Our results contribute to highlight Sedum benefits for a vegetated roof in such an area. Further investigations will be needed to assess if the green roof technology provides a very effective solution for building energy savings in cities under a tropical humid climate.