Life cycle environmental impact of different replacement options for a typical old flat roof

Abstract

Numerous strategies have been implemented to reduce the global environmental burden of construction activities in order to achieve sustainable development goals. However, with regard to renovating and retrofitting existing buildings, life cycle assessment (LCA)-based studies mostly focus on the improvement of a building’s energy performance rather than on the structural aspects of the retrofit itself. The present study assesses the life cycle environmental impacts of different replacement options for a typical old flat roof belonging to a masonry building. Three different structural options are considered: reinforced concrete joists and hollow clay blocks, steel joists and concrete slab, and reinforced concrete joists and polystyrene panels. The environmental analysis is based on a new approach wherein the structural and functional properties of a new flat roof are set as fixed requirements for the design of the different replacement options. A cradle-to-grave LCA-based study is then conducted for the environmental assessment of the entire retrofit process, including different waste scenarios. SimaPro software and IMPACT2002+ methodology are used for the LCA analysis, enabling quantification of the environmental impacts of the three flat roofing options by means of 4 endpoint and 15 midpoint indicators. The environmental contribution of each life cycle phase related to the replacement of the old flat roof is assessed. The results demonstrate that within the life cycle of each option, the use phase and the construction phase have the highest environmental impact, ranging from 60 to 70 % and 50 to 80 % of the total burden in the Climate Change/Resources and Human Health/Ecosystem Quality damage categories, respectively. Having initially set structural and functional constraints for the analysis, the results show that any of the different options exhibits an overall lowest environmental performance. Consequently, specific environmental burdens/categories can be identified to optimize the sustainable retrofit design. The work demonstrates that a comprehensive LCA-based approach can be used to effectively drive the design of structural and functional retrofit operations on existing buildings. This study also shows how a rigorous environmental analysis, conducted by implementing the proposed approach, can influence decision-making for the most sustainable design alternatives.