Extending the concept of high-performance buildings to existing dwellings

•Quantifies the impact of internal insulation on the floor loss area.•Assesses the impact of the floor loss cost on the building energy performance.•Presents the optimal thermal envelope for southern Europe climate.•Identifies the impact of the property value on the choice of insulation materials. The ongoing energy crisis in Europe is highlighting the role of the building sector in energy consumption, particularly in countries like Spain, where 90.4% of existing dwellings lack thermal efficiency. Encouraging homeowners to undertake renovations can prove challenging, especially when complex thermal insulation techniques are involved. This study defines the optimal renovation package for six residential building models for 90% of southern Europe climates. Three methodologies were employed for optimal selection: a conventional cost-optimal approach, a method considering the impact of internal insulation on floor loss, and a CO2eq emissions approach based. The findings reveal that, on average, the primary energy demand of existing buildings can be reduced by 57%, with potential savings reaching up to 75% for a cost-optimal approach. Internal insulation significantly has a significant impact on floor loss costs, accounting for up to 60% of a building's life cycle cost, where the property value plays a significant role in the choice of insulation material, especially when considering the same thermal resistance. On the other hand, the CO2eq emission-based approach results in buildings with lower energy demand but more costly. Choosing the most suitable methodology for life cycle assessment requires a balance between economic constraints and environmental considerations.