The greater insulation offered by green roofs can reduce the amount of energy needed to moderate the temperature of a building, as roofs are the site of the greatest heat loss in the winter and the hottest temperatures in the summer.
Green roofs cool down the temperature because of the direct coverage of plants and transpiration during daytime.
Susca et al. (2011) found that green roofs can save energy consumption from 40% to 110%.
Maiolo et al. (2020) found that in a Mediterranean climate, the lack of insulation layers in the green roof improves the energy performance both in summertime and wintertime (although in the latter case less significantly).
They argue that by not using insulated green roofs, the evapotranspiration would help cool the building passively.
They reported that:
In wintertime, green roof temperatures were higher between 0.2 to 4.6 °C, reducing the demand for heating.
In summertime, green roof temperatures were lower between 5 and 11.3 °C, reducing the demand for cooling.