- Rooftop trees have better thermal performance compared with typical green roofs.
- Rooftop trees reduce indoor temperature by up to 7.20 °C and cooling electric loads by up to 60%.
- Green roof performance varies by urban density and building type.
- Green roof rating schemes should use performance instead of coverage percentage.
There is an increased interest in including green roofs in building legislation to enable green infrastructure and improve the built environments. Yet, trees on buildings in particular, have received little attention. This paper presents a parametric study on the effect of nine green roof configurations on outdoor and indoor temperatures and the associated cooling demand under three urban densities by coupling ENVI-met and EnergyPlus simulation software. This study is novel as it introduces the performance of green roof configurations that include canopy trees and compares their performance with typical green roofs that include only low canopy vegetation. Results show that 1) green roof performance has a greater impact on reducing indoor rather than outdoor temperatures; 2) green roofs with trees perform better compared with green roof configurations without trees, reducing the indoor temperature by up to 7.20 °C and air conditioning electric loads by 60%; 3) green roofs with trees excel in thermal performance compared with typical green roofs, even if the latter have a higher green coverage percentage. Therefore, the authors recommend using green roof performance for green building rating and legislation instead of using green coverage percentage. Furthermore, as green roof performance varies with urban density and building type, the authors suggest specifying the most appropriate green roof configuration for each neighbourhood in smart city models to maximise the benefits and address the city’s needs.