Horizontal extensive green roofs in existing buildings. Part Two - Economic features

If the horizontal rooftop of an existing building matches suitable structural criteria about its bearing capacity and the overall load transferred to foundation elements, green roofs represent an efficient solution for energy and operational performances improvement, with proven effects specifically in storm-water runoff phenomena control and heat island effect mitigation. In this paper, with reference of an existing building and its technological content, a model for the evaluation of the probability of economic affordability is described, considering a rooftop refurbishment intervention in different technological scenarios: three rooftop finishing layers – loose gravel, washed gravel tiles, waterproof membrane – are replaced, alternatively, by a thermal insulated cool roof or by an extensive green roof.