Assessment of the green roofs thermal dynamic behavior for increasing the building energy efficiencies

The continuous city growth leads to the intensification of the Urban Heat Island effect (UHI) which involves several consequences for the in-habitant comfort. Countermeasures such as green roofs can mitigate the urban microclimate reducing the roof surface temperature and hence the surrounding air temperature. As most of the existing Italy building stock was built without or with poor thermal insulation, they need of interventions of energy retrofit. In particular, roofs are the component of the building envelope that are mainly engaged of both solar gains and thermal fluxes. Therefore, any interventions refurbishment should include the roof surface. This paper focuses on the analyses of the energy performance and the dynamic thermal behavior of a green roof implemented in an existing house-holiday situated in the south part of Sicily. Moreover, other two refurbishment scenarios that foresee the increase of the roof thermal insulation were analysed. Dynamic simulations have proven that the green roof reduce the energy needs, about 90% in the cooling period and 30% in the heating period; delays and attenuates the outdoor heat wave in comparison with traditional roofs, as well as diminishes the average daily temperature fluctuations. The reduction of the vegetated temperature area results about 10.0 °C lower than the one of a bare roof area.