A multi-criteria decision-making method for thermal insulation material selection in nZEB level questioned affordable multifamily housings

An affordable multifamily housing building archetype project was researched to improve the building envelope’s thermo-physical performance based on thermal insulation configurations to optimize the energy use, life-cycle cost, environmental impact, and thermal comfort with questioning nZEB concept. Five thermal insulation materials as extruded polystyrene (XPS), expanded polystyrene (EPS), rockwool (RW), glass wool (GW), and cellular glass (CG), were studied with four> attribute variations (thermal comfort, density, embodied carbon, and embodied energy) and five thickness variations (0.04, 0.08, 0.12, 0.16, 0.20 m). A total of 100 alternative scenarios> were obtained for the decision-making process, with four performance criteria to be evaluated in terms of energy, cost, thermal comfort, and environmental impact. Equal weights method (EWM), weighted sum method (WSM), and analytical hierarchy process (AHP) were examined for the multi-criteria decision-making among 46 scenariosvel. The analysis beyond the cost-optimal energy efficiency level, which varies between 64.89 and 72.62 kWh/m²a for primary energy use with a potential 10% further reduction, ensures the European Commission’s recommendations that target 50–70 kWh/m²a of primary energy use for housings in the continental climate to achieve nZEB. The best scenarios cover significantly the XPS at the head due to lover investment costs, where RW, GW, and EPS are followed among the best 10 scenarios, respectively. Besides, AHP provides a more effective distribution of weighting factors than the WSM where the best scenarios of the AHP covers 12 cm thermal insulation alternatives by balancing the investment costs and energy efficiency levels. The paper provides insight into thermal insulation material selection while searching for the advantages and priorities of thermal insulation materials’ attributes beyond the cost-optimal energy efficiency level to reach the nZEB range.