Horizontal extensive green roofs in existing buildings. Part One - Technological features

Green roofs represent covering solutions, anciently applied, capable of significant impacts on many features of social and environmental sustainability: reduction of energy consumption, mitigation of microclimate in high-density urban contexts, hydrological cycle control. In Mediterranean climate we recognize an interesting potential for their implementation in Italian existing building heritage. With regard to energy performance, green roofs offer best results in summer; in winter, however, there are no noticeable advantages, compared to a traditional insulated roofing. At a larger scale, green roofs effectively counteract heat island effect acting on radiative heat exchanges. Their permeability, finally, allows an appropriate reduction of stormwater runoff rates directed to sewage system, so green roofs are connoted as effective solutions in containing climate change effects. This paper aims to assess briefly extensive green roofs implementation potential in existing buildings plane coverings. These interventions require careful feasibility assessment, with reference to structural, architectural and economic features; current mandatory legislation about buildings structural safety allows some argumentations concerning building types and constructional techniques.