Gröna taks samhällsekonomiska nytta och kostnader

Sammanfattning: City densification in Sweden has decreased the amount of green areas in Swedish cities. This undermines the existing ecosystem services that could for instance provide climate change mitigation and adaption. Green roofs are considered to be a product that can strengthen or substitute the urban ecosystem services produced by natural vegetation. This paper investigates whether retrofitting green roofs on housing buildings is beneficial and financially viable from a societal point of view. The method used to determine this is a Cost Benefit Analysis (CBA) with guidelines from the Swedish Environmental Protection Agency. The analysis consists of describing and estimating the effects green roofs have on storm water management, mitigation of urban heat island, energy consumption in housing, noise pollution, air quality, biodiversity and amenity for people. Both extensive and intensive green roofs were analyzed. Retrofitting green roofs have positive effects on all the previously mentioned parameters but these effects must be weighed against the installation costs and maintenance of green roofs. The analysis concludes that the most significant benefits are sound insulation, energy saving due to cooling and improvement of storm water management. The amenity value is viewed to be a strong as well. The cost benefit analysis shows that green roofs are a good investment for society.