Upcycling volcanic ash from Mount Etna for green roof system: a circular strategy for energy-efficient and sustainable buildings

This paper proposes an integrated methodology to assess volcanic ash from Mount Etna suitability as sustainable material for green roof assemblies, aimed at valorising local waste and improving building energy performance. Laboratory tests were conducted to evaluate volcanic ash engineering properties and compare with conventional materials, as expanded clay and expanded perlite. The experimental results on thermal conductivity, density, porosity, water retention capacity, and permeability confirmed that volcanic ash offers adequate insulation and hydrological properties for substrate and drainage applications. To complement the laboratory phase, virtual energy modelling and simulations were performed to assess the impact of different green roof configurations under various climatic conditions, isolating the energy contribution of each layer combination. Results showed that ash gains adequate insulation comparable to traditional/commercial green roof materials, with particular energy effects on colder climates. Also, a Multi-Criteria Decision-Making (MCDM) approach was implemented to identify the optimal compromise solution, integrating performance data with environmental and economic criteria. The proposed methodology considered both current and enhanced sustainability scenarios through a weight-driven decisional matrix developed by field experts. The conducted research revealed that volcanic ash represents a valid alternative both in terms of performance and sustainability, positioning in a high-ranking position. Finally, the combined use of laboratory tests, energy simulations, LCA/LCC analyses, and MCDM confirms that volcanic ash can match or outperform conventional materials while reducing embodied energy, costs, and environmental impacts. This study demonstrates a replicable circular economy strategy for volcanic by-products, supporting more sustainable and resilient urban green infrastructure. • Innovative and sustainable volcanic ash use is identified. • Volcanic ash is technically suitable for application in green roof systems. • Superior building energy improvement is observed for colder climates. • MCDM ranked technical solutions in real/enhanced sustainability scenarios. • Green alternatives to traditional polluting disposal system are provided.