Balancing energy efficiency and embodied carbon in building renovation: a Pareto front optimization approach for interior insulation selection

Purpose The aim of this study is to develop a framework for evaluating and comparing design options and to enable designers to quickly assess the energy and environmental impacts of different insulation materials relative to optimal conditions. Specifically, the research aims to develop a method for selecting insulation materials that prioritizes minimizing their embodied carbon footprint while achieving near-zero energy consumption post-renovation. Design/methodology/approach The research employed a multi-objective optimization methodology to balance energy efficiency and the embodied carbon footprint of insulation materials. The study focused on renovating the interior envelope of a 65-m2 apartment unit in Tehran, Iran. The two objective functions were minimizing the building’s annual energy consumption over a 60-year lifespan and minimizing the environmental impact (embodied carbon) of the insulation materials throughout their life cycle. A total of 37 insulation material combinations were analyzed using DesignBuilder (EnergyPlus) for energy performance and SimaPro for life cycle assessment. The trade-offs between these two objectives were visualized using a Pareto front, which was generated by applying the NSGA-II genetic algorithm in MATLAB to identify the set of optimal, non-dominated solutions. Findings The optimization yielded a Pareto front of optimal solutions. By prioritizing solutions closest to this frontier, four optimal scenarios (T1–T4) were ranked. The top-ranked scenario, T4, demonstrated the best overall compromise between the two objectives (the shortest distance to the Pareto curve), utilizing a layering of 2.5 cm PIR and 3 cm Phenolic insulation. This scenario resulted in a total environmental impact of 809.64 kg CO2 eq. and a total energy consumption of 2 × 106 kW h over 60 years. Originality/value The originality lies in developing and applying a simplified, two-criteria framework – using a Pareto front approach and the NSGA-II algorithm – specifically to the problem of selecting insulation materials for the interior side of the building envelope in older residential apartments, a critical gap for renovations in regions like Iran. This method explicitly addresses the trade-off that solely reducing operational energy can inadvertently increase embodied carbon. The resulting framework provides a non-complex, calculation-free visual aid for decision-makers.