LCA- and nZER-based methodology for identifying optimal low environmental impact interventions for existing buildings

Reducing the energy demand in the building sector appears to be the most important aspect to make them energy efficient. Opting for durable minor interventions results in further reduction of embodied carbon. This paper proposes a method which combines the evaluation of the environmental impact of interventions together with the visual preservation of buildings. A new indicator, the Embodied Impact of Intervention (EII), was defined to evaluate the overall environmental impact considering three indicators within the Life Cycle Assessment: Global Warning Potential (GWP), Primary Energy Non-Renewable (PE-NRe), and net-Fresh Water (FW) offering the stakeholders a holistic view for selecting the most sustainable solutions for interventions in existing buildings. The methodology has been tested to a benchmark, (i.e., masonry wall components), considering low, medium, and high visual impact scenarios, and a lifespan of 100 years. A direct proportionality is shown between GWP and PE-NRe, whereas FW does not have a singular relationship with the other indicators as it is mainly influenced by the material production. High GWP values occur in scenarios in which Nature Based Solutions (236.82 kg_CO2eq) and Building-Integrated Photovoltaic panels are implemented (798.09 kg_CO2eq), being ≈2.7 and ≈9 higher than the same High Visual Impact scenarios without mitigation solutions. It was found that the visual impact of the interventions may not align with the corresponding EII, resulting in dichotomous scenarios with medium visual impact and low EII, or high visual impact and medium EII. In Low-Income Countries, using recycled materials can minimize the production phase, reducing EII, energy efficiency, energy usage and waste, to accomplish the Sustainable Development Goal in the long-term.